Answer:

You can provided you know how to change spark plugs, check (and adjust, if necessary) the ignition timing, idle speed and idle mixture (carburetors only) on your engine. 

If you can reach the spark plugs on your engine, you should be able to change them yourself. All you need is a plug socket, ratchet wrench, extension, and feeler gauge to set the plug electrode gap. If you're working on an engine with adjustable timing, you'll need a timing light to make sure the timing hasn't changed (it shouldn't have unless somebody messed with it). And you'll need a tachometer to set the idle speed correctly. 

Engines that have electronic ignition and a sealed carburetor or fuel injection require very little maintenance beyond replacing the spark plugs every 30,000 miles, replacing the air and fuel filters annually (or as needed), changing the PCV valve (every 30,000 to 50,000 miles) and changing the oil and filter (every 3,000 miles or six months is usually recommended). 

When replacing these items, you should also give your engine a good "once over" to make sure there are no obvious problems such as fluid leaks, loose or damaged wires, belts, or hoses, etc. Checking things like compression and intake vacuum are not required, but can reveal a lot about the overall condition of your engine. 

WHAT TO INCLUDE: 

A comprehensive "tune-up" should probably include all of the following: 

     Replacing the spark plugs (be sure to gap to specs) 
     Inspect the rotor (replace only if necessary) 
     Inspect the distributor cap (replace only if necessary) 
     Check timing (adjust if necessary) 
     Inspect spark plug wires (replace only if necessary) 
     Check idle speed (adjust as needed) 
     Check choke (carbureted engines only) 
     Check compression (to monitor valve & ring wear, requires a compression gauge) 
     Check manifold intake vacuum (to check for leaks, or valve and ignition problems, requires a vacuum gauge) 
     Check battery/charging voltage (to detect charging system problems) 
     Inspect & clean battery posts and cable connections 
     Inspect air filter (replace if dirty) 
     Replace fuel filter (for preventative maintenance) 
     Replace PCV valve 
     Check vacuum hoses (replace only if cracked or loose) 
     Check all vital fluid levels (engine oil, transmission fluid, coolant, brakes and power
     steering) 
     Inspect belts & hoses (replace as needed) 
     Check safety items such as lights, wipers, tires (including inflation pressure), and horn. 
 
 
 TIMING

How do you check or adjust ignition timing on an engine with a distributor less ignition system? 

Answer:

You can't do either on many engines, but checks and adjustments are still possible on others. 

On some distributorless ignition systems, timing is fixed and cannot be adjusted. Nor are any timing marks provided on the crankshaft pulley for reference checks. If there are any problems (like a bad crankshaft position sensor), the onboard computer is supposed to pick it up and illuminate the Check Engine light. Otherwise, you have to assume everything is fine. 

On other engines without distributors, the crankshaft position sensor and/or cam position sensor allows a certain amount of adjustment. Loosening and rotating the sensor's position has the same effect on advancing and retarding timing as rotating a distributor. Timing marks on the crankshaft pulley are usually provided so a conventional timing light can be used to check timing. 

To check timing, attach a timing light to the number one spark plug wire. Use the light to illuminate the timing marks on the crankshaft pulley as the engine idles. Refer to the engine emissions decal or a shop manual for the timing specs. 

To adjust timing, loosen the crankshaft or camshaft sensor. Then rotate the sensor's position in the same direction as the crankshaft or camshaft turns to retard timing, or in the opposite direction to advance timing. 

On some engines timing can also be checked electronically through the computer system itself by plugging a "scan tool" into the computer's diagnostic connector. 
 

My steering feels loose. Any ideas why? 

Answer:

The most common causes of steering looseness include worn tie rod ends, a worn idler arm or center link (on vehicles without rack and pinion steering), a worn steering gear or a worn steering rack. 

Normally, your steering wheel should have no more than about a quarter inch of play. Any more means something is worn or loose and needs to be fixed. 

WARNING: Don't put off having your steering looked at because a failure of a critical component could cause loss of steering control! 

The inner and outer tie rod ends should have no perceptible looseness. Worn or loose tie rod ends are especially dangerous because if one pulls apart you'll lose steering control. Worn tie rod ends can also cause rapid tire wear. 

If you have a rear-wheel drive vehicle with conventional steering (not rack and pinion steering), the idler arm should have no more than the specified amount of maximum play. Refer to a manual for the specs and recommended procedure for checking it. Checking idler arm play usually involves pulling on the arm with a specified force and measuring how much the arm deflects. 

If your vehicle has a lot of miles on it, the steering gear or rack itself may be worn. On
conventional steering boxes, there's usually an adjustment screw that can be used to take some of the slack out of the system. With rack and pinion steering, though, adjustment is usually little help because the rack develops center wear. If the pinion is adjusted to compensate, the rack may bind when turned to either side. The only cure for a center wear condition is to replace the rack with a new one (an entire new rack assembly). 

OTHER CAUSES 

Sometimes the steering will feel loose because of a worn U-joint coupling in the steering column. Loose or worn wheel bearings can also make the steering wander and feel loose. 
 

My power steering feels stiff when I first start my car, but then feels normal after I've driven the car awhile. How come? 

Answer:

This is called "morning sickness" and has nothing to do with being pregnant. The condition is caused by wear in the spool valve housing on certain power steering racks -- notably GM front-wheel drive cars. 

When the car is first started, the rack is cold and clearances in the spool valve are at their greatest. Hydraulic pressure from the power steering pump leaks past grooves worn in the aluminum spool valve housing. This causes a loss of pressure and increases steering effort. The steering feels stiff with little or no power assist. As the car is driven, the rack warms up. This decreases the clearances inside the spool valve housing, which reduces the leakage past the grooves. More pressure goes to where it is supposed to go and the steering becomes easier as power assist returns. 

The "fix" for this condition is to replace the rack with a new one (preferably with a cast iron spool valve housing) or a remanufactured rack that has a stainless steel sleeve pressed into the aluminum housing. 

  SMELLY CAR

Answer:

You probably have an oil leak on your engine that is dripping oil on an exhaust manifold or pipe. The most likely cause is a leaky valve cover gasket. 

Open the hood and visually inspect your engine (engine off, of course). Look for wet, oily streaks or a buildup of greasy deposits on the sides of your engine near the exhaust manifold. You may also have noticed some oil spots on your driveway, or a slight increase in oil consumption (check the oil level on the dipstick). 

If oil is leaking past the valve cover gasket, the gasket will have to be replaced. 

OTHER ODORS 

If you don't see an oil leak and continue to smell something unusual, it could signal something more serious. Overheated wiring may also produce a burnt smell, but one that has a sharper, more pungent or caustic odor. This is nothing to ignore because it may result in a fire. Have a professional inspect your wiring. 

An overheated automatic transmission or one that's filled with badly oxidized fluid (because nobody ever changed it) can also produce a burnt smell. To check the fluid, remove the transmission dipstick. If the fluid has a dark brown color or smells burnt, it is long overdue for a change. It might also mean your transmission is on the verge of calling it quits, too -- especially if it has been shifting erratically, slipping or otherwise acting up. Transmission repairs are very expensive and usually require replacing the transmission with a new or rebuilt unit. 

If you smell a "rotten egg" odor (hydrogen sulfide), it may mean your engine is running lean or that the catalytic converter may not be functioning properly. Some vehicles (Ford mostly) have had problems with persistent rotten egg odors from the converter. Apparently, it has something to do with the mix of catalysts used to manufacture the converters. Replacing the converter with a "revised" model usually cures the problem. 

MY ENGINE WON'T START 

Answer:

You may have an ignition, fuel delivery or compression problem. 

1. Check for spark first. If there's no spark, you may have a failed ignition module, ignition pickup, ignition coil or open in the ignition circuit (bad ignition switch or neutral safety switch). 

2. If you have spark, check for fuel. On carbureted engines, remove the air cleaner, hold the choke open, look down the carburetor throat and work the throttle linkage. If you don't see any fuel squirting into the carburetor, the problem may be a stuck needle inlet valve in the carburetor, a bad fuel pump, a plugged fuel filter, a plugged or frozen fuel line, an obstructed fuel tank pickup screen, or no fuel (or water contaminated fuel) in your tank. 

3. If you have spark and fuel, your timing chain or belt may have broken or slipped. If your engine has a distributor, remove the distributor cap and see if the rotor turns when the engine is cranked.
No movement would tell you the timing belt or chain (or possibly the cam itself) is broken.
Another alternative is to remove the valve cover to see if the valves are opening and closing. This too will show you if the cam drive or cam is broken. 

If a cam belt or chain has "slipped a tooth," throwing valve timing off, the valves will still open and close, and the rotor inside the distributor will still turn. But the engine won't develop enough compression to start. A compression check can help you find this kind of problem. 
             

  WHAT CAUSES A NO SPARK CONDITION

Answer:

The best way is to methodically check each component until you've isolated the fault. But many people start replacing things until they eventually stumble on whatever was causing their problem (which is a very expensive and time-consuming way to solve a no start problem). 

If you're certain the ignition system is not creating a spark (Further information is available on getting a spark.), you can assume that either the coil is defective or something in the electronic circuitry that controls the coil is defective. 

Most distributor type electronic ignition systems have either a magnetic pickup or "Hall effect" sensor that generates a signal as the distributor shaft rotates. On distributor less ignition systems, the trigger signal is generated by a Hall effect or magnetic crankshaft position sensor (and cam position sensor in many applications). The trigger signal goes to the ignition module, which switches the ignition coil on and off to fire the spark plugs. If the pickup or Hall effect switch is not producing a signal, or if the ignition module is not processing the signal, the coil won't fire. 

COIL CHECKS 

Ignition coils are pretty simple (just a set of copper windings around an iron core sealed in plastic), so there's not much that can go wrong with them. They do fail occasionally, but usually the part that fails is something more vulnerable like the ignition module, the pickup in the distributor or the wires that connect to the pickup or the module. 

The coil can be ruled out as a possible cause by checking it's "primary" and "secondary" resistance with an ohmmeter. Primary resistance is checked between the positive and negative coil terminals. As a rule, primary resistance should be two ohms or less. Secondary resistance is tested between the high voltage terminal and the negative terminal. Secondary resistance should be high, ranging anywhere from 8,000 to 20,000 ohms. The exact specs will vary from one application to another, so refer to a manual for the specifications for your vehicle. 

NOTE: On some distributor less ignition systems, the individual coils in the coil pack assembly can be replaced if only one coil is defective. On others, the coils cannot be replaced separately and the entire unit must be replaced if any coil, or the coil module, is bad. 

WIRING CHECKS 

CAUTION: Don't disconnect or unplug any connectors without first making sure the ignition is off. Breaking a connection while voltage is flowing in the circuit can create a voltage surge that may damage electronic components. 

Check all the connectors at the distributor, module and coil to make sure they're tight and
corrosion-free. It doesn't take much to disrupt the primary ignition circuit. A visual inspection won't necessarily reveal all such problems because "invisible" corrosion can create enough resistance to disrupt a low voltage circuit. You may have to back probe both sides of a connector with an ohmmeter to see if there is resistance in the link. 

Next, remove the distributor cap (if your engine has one) and inspect the wiring connections on the pickup (and module if the module is located inside the cap as is the case with most GM systems, or on the side of the distributor as is the case with many Ford systems). The flexing of the distributor can sometimes cause hairline cracks in the wires or their insulation creating an open in the circuit. 

PICKUP CHECKS 

If you don't find any problems here, check the resistance of the pickup in the distributor (refer to a manual for the exact specs). An open or short here can prevent the pickup signal from reaching the module. The exact test procedures are so varied that we'll summarize by saying that most checks involve using an ohmmeter to measure the resistance of a magnetic pickup or a voltmeter to check voltage readings in the Hall effect sensor circuits. If the readings are out of range, the pickup or sensor needs to be replaced. With Hall effect sensors, it's also important to make sure the sensor is receiving voltage because it can't generate a signal without voltage. Refer to a manual for the specific diagnostic procedure for your vehicle. 

NOTE: On engines with computerized controls, loss of the pickup signal will usually set a fault code in the computer. On vehicles with distributor less ignition systems, a bad crankshaft or camshaft sensor will also set a code. To check for such a code, you'll need a scan tool -- unless the computer has a "manual" diagnostic mode that displays "flash" codes (blinking lights) when certain terminals on the diagnostic connector are jumped or grounded. Refer to a manual for the code retrieval procedure. 

MODULE CHECKS 

Ignition modules frequently fail for three reasons: heat, vibration or voltage overload. Excessive heat can damage sensitive electronic chips. GM ignition modules and Ford TFI modules, in particular, rely on a layer of grease under the module to help carry heat away from the electronics. If someone replaced the module and forgot to apply the grease, the module may have failed due to overheating. The leads that connect the module to the wiring are also vulnerable to breakage, often as a result of vibration. Finally, a module can be destroyed if the high secondary voltage in the distributor somehow finds a path to the module. 

In some applications, modules can be checked by using a high impedance (10 megohms) digital ohmmeter to measure resistance between various terminals. If any of the measurements are out of spec, the module is defective and needs to be replaced. But on most applications, a process of elimination is used to isolate a bad module. Or, a "known good module" is substituted for the old one to see if it cures the problem. If the engine starts, the old module must have been bad. If it still doesn't start, then it's something else. The problem with this technique is that the new module may be damaged if there's a short in the wiring that caused the old module to fail. 

COMPUTER CHECKS 

Most electronic ignition systems will start even if the computer is defective or disconnected. The computer plays an "intervening" role and modifies spark timing by delaying or advancing the pickup trigger signal or module switching of the coil. In spite of the fact that many people blame the computer for anything that goes wrong, the fact is the computer is pretty reliable. Most problems can be traced to opens in the wiring harness or loose or corroded connectors. 

A scan tool is required to check the computer for ignition-related fault codes, unless the system provides a manual flash codes. Refer to a manual for the diagnostic procedure for your vehicle. 
 

                     LACKS POWER AT HIGH SPEED

Answer:

You most likely have one of two problems: a fuel line restriction or an exhaust restriction. 

FUEL RESTRICTION 

A plugged fuel filter, crushed fuel line or clogged pickup screen inside the fuel tank can all starve your engine for fuel. Enough fuel may get through for the engine to start and run at low speed, but when more fuel is needed it can't get through resulting in loss of power at high speed. The same kind of problem can also be caused by a weak fuel pump. But fuel pumps usually quit altogether when they fail. 

Inspect the fuel line from the tank to the engine. If you don't see any obvious damage, try replacing the fuel filter. If that doesn't help, blowing out the fuel line with compressed air from the engine towards the fuel tank may help dislodge a blockage and debris from the pickup screen. If the pickup screen in the tank is clogged with rust and debris, the tank will have to be removed so the screen can be replaced and the tank cleaned. 

Fuel pressure can also be checked by teeing a suitable gauge into the fuel line. If pressure is very low (refer to a manual for the specs), the pump probably will need to be replaced. 

EXHAUST RESTRICTION 

As for an exhaust restriction, the easiest way to check for this condition is to hook up a vacuum gauge to a vacuum port on the intake manifold or throttle body. If vacuum is low and continues to drop as the engine runs, it's telling you pressure is backing up because of a restriction in the exhaust. The most likely culprit is a clogged catalytic converter. 

If the converter has overheated, it may have melted internally. This would restrict the flow of gases through the converter and create a serious backpressure problem that would cause a loss of power at high speed. If the blockage is complete, the engine may start then die and not run at all. 

Other causes here may include a crushed exhaust pipe (a visual inspection should find this easy enough), a double-walled pipe that has collapsed internally, or a muffler that has become clogged with rust (rare, because they usually blow out). If you suspect an exhaust restriction, temporarily disconnect the head pipe from the catalytic converter (which is no easy task because the bolts will probably be rusted solid). If the engine now runs normally, you have an exhaust restriction. Inspect the converter and replace it if needed. 

NOTE: If the converter is plugged, it failed because something else caused it to overheat. Causes include misfiring spark plugs and leaky exhaust valves. The underlying problem needs to be identified and corrected before the converter is replaced otherwise the new converter will suffer the same fate. 

  DIRTY FUEL INJECTORS

Answer:

"Dirty" is actually a misnomer. Rarely are injectors clogged with dirt. Rather, they are usually clogged or restricted by a buildup of fuel varnish deposits. This reduces the amount of fuel that the injector sprays, which in turn may cause the engine to run lean and misfire, hesitate or stall. 

A fuel injector is nothing more than spray nozzle. With mechanical injectors, a spring loaded valve allows fuel to squirt out of the nozzle when line pressure overcomes spring tension that holds the valve shut. With electronic injectors, a spring-loaded solenoid pulls open a pintle valve or ball type valve when the injector is energized by the computer. This allows the pressurized fuel in the fuel rail to flow through the injector and squirt out the nozzle. 

Injectors come in a variety of styles. Early Bosch style injectors have a pintle valve and are the ones most prone to clogging. In 1989, General Motors introduced its new "Multec" style injectors which have a ball valve design and are claimed to be more resistant to clogging. Other injectors have a disc-valve design that is also said to resist clogging. 

The truth is ANY injector can clog. Nobody's injectors are immune to this kind of problem, but some are obviously better than others. 

Problems can occur even with a slight buildup of deposits. Because the injector orifice is so small, it doesn't take much crud to restrict the flow of fuel or to disrupt the spray pattern. For good combustion, the injectors must produce a fine cone-shaped mist of fuel vapor. Wear or deposits in the nozzle can create "streamers" of liquid fuel that vaporize and burn poorly. This, in turn, can cause hesitation, emissions and performance problems. 

INJECTOR CLEANING 

The cure for a set of clogged injectors is cleaning -- or replacement if they're too badly clogged to respond to cleaning. Injectors are expensive to replace. New domestic injectors sell for $60 to $100 each, with new import injectors fetching $125 to $175 each. Injectors should only be replaced as a last resort. 

If your injectors are clogged, they can be cleaned with pressurized solvent, or removed for off-car cleaning. There are also fuel tank additives that claim to clean clogged injectors, but the cleaning such products do is usually minimal. So save your money and put it towards a professional cleaning. 

There are do-it-yourself on-car injector pressure cleaning kits that are similar to the equipment professionals use. But some of these kits can be tricky or even dangerous to use. Our advice is to let a professional do it. 

On-car injector cleaning involves feeding solvent under pressure into the injector fuel rail or supply line. The concentrated solvent passes through the injectors and loosens and washes away the accumulated varnish deposits. The results are usually good, and make a noticeable difference in idle smoothness, emissions and fuel economy. 

If your injectors are really clogged and fail to respond well to on-car cleaning, off-car cleaning using special fuel injection cleaning equipment would be the next logical option. Some of this equipment is designed to "reverse" flush the injectors so any debris that's trapped inside the injector or above the inlet screen will also be removed. Off-car cleaning also allows a mechanic to observe the spray pattern of the injectors to make sure there aren't any streamers or problems. Off-car cleaning is more expensive because of the labor involved to remove the injectors, but the results are usually better. 

KEEPING INJECTORS CLEAN 

The best way to minimize or eliminate the need for injector cleaning is to use a quality brand of gasoline that contains sufficient detergent to prevent varnish buildup. Most brand name gasolines today have enough detergent to do this. As a rule, premium grades usually contain a somewhat higher concentration of cleaners. 

You can also use fuel tank additives to keep your injectors clean. Such products really aren't necessary if you're using quality gasoline. But if you're buying the cheapest gas you can find, using an additive might be good insurance. 
 
 

HARD STARTING WHEN COLD 

Answer:

If your engine has a carburetor, the hard starting problem is most likely choke related. If the engine cranks normally and the spark plugs are not worn or dirty, the choke probably needs to be repaired or adjusted. 

The choke may be set too rich or too lean. Either way can cause hard starting. Inside the choke housing is a bimetal spring that regulates the tension on the choke according to temperature. If this spring is broken, the choke will not operate. If the choke linkage is rusty or jammed with varnish deposits or dirt, it may stick or not operate smoothly. Cleaning with carburetor spray or solvent may help alleviate a sticking problem. 

On older fuel injected engines, a separate "cold start" injector is used to spray additional fuel into the intake manifold when a cold engine is first started. If this injector is not working, the engine can be hard to start. The injector is controlled by a timer and relay, so if either of these components is defective it can prevent the cold start injector from doing its job, too. 

If your engine cranks slowly, your cold starting problem is not fuel related, but may be due to a weak battery, loose or corroded battery cables, or a weak starter. 

Check for obvious problems first. Remove, clean and inspect the battery cables (both ends). Then check battery charge and condition. (More information on the condition of your battery and battery recharging is available.) If the battery charge is low, recharging the battery may temporarily solve your problem. But there's a reason why your battery is low. You probably have a charging system problem that requires further diagnosis. (More information on alternators is also available.)
If your battery is more than four or five years old, it is probably near the end of its service life and needs to be replaced. A "load test" will tell you if it still has sufficient cranking capacity to provide reliable cold starting. 

Slow cranking during cold weather (below freezing) can also be caused by oil that is too thick. A high viscosity oil such as straight 30 or 40 weight oil in the crankcase can make an engine very difficult to crank when the temperature drops. Switching to a lighter multi viscosity oil such as 10W-30 or 10W-40 should solve this problem. 
 

 HARD STARTING WHEN HOT

Answer:

Hot starting problems are usually fuel related. When a hot engine is shut off, the temperature of the engine and everything on it continues to rise for awhile as the engine undergoes a period of "heat soak." This can cause fuel to boil inside the carburetor bowl, fuel lines and fuel filter. When you attempt to restart the engine, "vapor lock" obstructs the flow of fuel and the engine doesn't want to start. 

This is much less of a problem on fuel injected engines because the fuel is usually under much higher pressure inside the injectors and fuel line. Even so, a fuel line routed near an exhaust manifold or a fuel rail that's exposed to a lot of heat may still suffer the same kind of problems. 

Heat soak problems such as these can sometimes be cured by wrapping insulation around affected fuel lines, and/or installing an insulating spacer or heat shield under the carburetor. 

A SEASONAL PROBLEM 

Hard starting tends to be a seasonal problem, but may be worse in the early months of spring when refiners are switching fuel blends. Gasoline refiners produce fuel with a slightly lower volatility rating (called "Reed vapor pressure") during hot summer months because lower volatility fuel is less likely to boil and cause hot starting problems. During the winter, they switch to a higher volatility fuel because it makes cold starting easier. But if you still have "winter" grade fuel in your tank when warm spring weather arrives, you may experience some hot starting problems. The problem will go away, however, as soon as the refiners in your area switch to their summer grade fuel. 

OTHER CAUSES 

Hot starting problems can also be caused by cooling problems that allow your engine to run too hot (the pistons swell up and may scuff the cylinder walls), or excessive resistance in the starter motor that causes the engine to crank slowly. A starter "amp draw" test can be used to check the condition of your starter. Also, many starters have small "heat shields" to protect them from heat radiating from nearby exhaust pipes or manifolds. If the shield is missing, the starter may get too hot and bind up. 

STEADY MISS, BAD FUEL MILEAGE

Answer:

A steady miss indicates one of three things: a cylinder that isn't firing because of an ignition problem, a cylinder that isn't firing because it isn't receiving fuel (multipoint fuel injected engines only), or a cylinder that has lost compression. 

The first step in diagnosing this kind of problem is to identify the dead cylinder. A professional mechanic can do this quickly by hooking the engine up to an ignition oscilloscope and displaying an ignition raster pattern. The dead cylinder will show a firing voltage that is significantly higher or lower than its companions depending on the nature of the problem. He might also do a "power balance" test and/or a compression test to find the dead cylinder. 

One way you can find a weak or dead cylinder is to momentarily disconnect each of your engine's spark plug wires one at a time while the engine is running. When the plug wire is removed from the spark plug, there should be a big drop in idle speed and idle smoothness. When you pull a wire and there's little or no change in idle speed or quality, you've found the bad cylinder. 

It makes no difference whether you remove each plug wire from the spark plug or the distributor (or coil pack on distributor less ignition systems). The idea is to simply disconnect each cylinder for a moment to see if it makes any difference in the way the engine runs. The one that makes no difference is the problem cylinder. 

CAUTION: Disconnecting spark plug wires while the engine is dangerous because you risk
getting shocked. You can minimize this danger one of several ways. One is to wear rubber gloves and use insulated spark plug wire pliers to momentarily disconnect each plug wire. Another is to make sure no part of your body is touching or leaning against any metal surface on the vehicle (the fender, hood, grille, etc.). Or, you could turn the engine off, remove a plug wire, restart the engine, note any change in idle, then repeat for each of the remaining spark plugs. 

IGNITION DIAGNOSIS 

If you disconnect the plug wire from the spark plug and hold the end of the wire close to the plug terminal or other metal surface, you should see a spark and/or hear a crisp snapping noise if voltage is getting through the wire. No spark would tell you the plug wire is bad, voltage is arcing inside the distributor cap (remove and inspect the cap for cracks and carbon tracks -- replace if any are found) or a dead coil on a distributor less ignition system (Note: on most distributor less ignition systems, each coil fires two cylinders. So if both cylinders are dead, you know for sure the coil is not working. If only one cylinder is dead, however, it's not the coil). 

If all of the plug wires seem to be sparking okay, the next step would be to remove the spark plug in the problem cylinder. Fouling is a common cause of ignition misfire. Examine the end of the plug. If the electrode is covered with deposits, clean or replace the spark plug. Also, note the type of deposits on the plug. Thick, black, wet or oily-looking deposits would tell you the cylinder is burning oil (probably due to worn valve guides, rings and/or cylinder wall). If the deposits are a powdery black, the cylinder is running too rich (probably due to a leaky injector on a multipoint fuel injected engine). If the deposits are brown or gray, it indicates a normal buildup. However, the plug may be fouled because it hasn't been changed for a long time, because it is the wrong "heat range" for your engine application (you need a hotter plug), or because of frequent short trip stop-and-go driving. 

In any event, if the plug is fouled you should probably remove, inspect and clean or replace all of the spark plugs. 

FUEL DIAGNOSIS 

If the dead cylinder is receiving spark through the plug wire and the spark plug itself appears to be okay (not wet or fouled), and your engine has multipoint fuel injection you may have a dead fuel injector. 

To check for this kind of problem, start the engine and place your finger on the injector. You should feel a buzzing vibration if the injector is working. No buzz means the injector is either defective or it is not receiving a voltage signal through its wiring harness. You can check for the presence of voltage with a 12 volt test light or voltmeter. Disconnect the injector wiring connector and attach the test light or voltmeter between the injector and connector. If the light doesn't flash or you don't see a voltage reading when the engine is running, it indicates a wiring or computer problem that will require further diagnosis. If voltage is getting through but the injector isn't working, then the injector is defective and needs to be replaced. 

Sometimes the injector will appear to be working but really isn't. It will be receiving voltage and buzzing as normal, but because it is clogged up with varnish deposits little or no fuel is actually being squirted into the cylinder. If ignition and compression are both okay in the bad cylinder, therefore, it would tell you the injector is clogged. On-car cleaning may reopen the clogged injector is the varnish isn't built up too thick. But a completely clogged injector usually doesn't respond well to this type of cleaning. It either has to be removed for off-car cleaning (which may or may not succeed id reopening it) or be replaced. 

COMPRESSION DIAGNOSIS 

If the dead cylinder is getting spark and fuel, the only thing that's left is a compression problem.
The most likely causes here would be a leaky valve (probably an exhaust valve since they run much hotter than intake valves and usually fail or "burn" first), a blown head gasket (this usually involves two adjacent cylinders, however), or a rounded or badly worn cam lobe. 

A compression check will verify if the cylinder is developing its normal compression. Little or no compression would verify any of the above problems. A leakage test could also be used to further diagnose and identify the nature of the problem (valves, head gasket or cam). Air leakage through the exhaust port would indicate a bad exhaust valve. Air leakage back through the intake manifold would indicate a bad intake valve. Air leaking into an adjacent cylinder would indicate a blown head gasket. Minimal leakage would indicate a rounded cam lobe. 

Leaky valves would require removing the cylinder head and having a valve job performed. A leaky head gasket would require removing the head and replacing the gasket (and probably resurfacing the head to restore flatness). A cam problem would require removing and replacing the camshaft and lifters (old lifters should never be reused with a new cam). 
 
 

HOW DO I TELL IF I NEED A NEW FUEL FILTER

Answer:

The only way to tell for sure is to remove the filter and blow through it. If there's little resistance, the filter is still okay and does not need to be replaced. But if there's more than minimal resistance, the filter is dirty and should be replaced. 

CAUTION: Gasoline is poisonous, does not taste very good and may burn sensitive lips. So don't hold the filter to your mouth to blow through it. Instead, attach a short piece of clean rubber hose to the filter and then blow through the hose to test the filter. 

FILTER PROBLEMS 

A completely plugged fuel filter will stop your engine cold by choking off the flow of fuel to the carburetor or injectors. The engine may not start, or it may start, then stall and die. 

Some filters have a spring-loaded bypass, however, that allows fuel to bypass the filter element if it becomes clogged. Fuel continues to flow, but it may carry dirt to the carburetor or injectors, which can create additional problems. 

A partially restricted filter will usually pass enough fuel to keep the engine running at idle or low speed, but may starve the engine for fuel at higher speeds or loads. So your engine may run fine putting around town, but sputter and lack power when you try to drive at highway speeds or pass someone. 

TANK FILTER 

Located inside the fuel tank is a screen or mesh sock that acts like a prefilter to keep big pieces of dirt and rust from being drawn into the fuel pickup tube or tank-mounted electric fuel pump. If the screen becomes clogged with debris, it can have the same effect as a plugged or dirty fuel filter. Therefore, if you've been experiencing a fuel starvation problem and have replaced the fuel filter --and it didn't help -- the screen in the tank is probably the culprit. To clean or replace it, the fuel tank usually has to be removed. 

WARNING: The fuel tank must be drained prior to removal. The fuel must be stored in a sealed "approved" container. The battery should also be disconnected to prevent any accidental sparks from an in-tank electric fuel pump connection from igniting the vapors. Do not smoke when working on the fuel tank, filter or fuel lines, and keep all other sources of ignition away (electric heaters, pilot lights, etc.) from the work area. 

FILTER REPLACEMENT 

Replacing the fuel filter periodically (every year or so) for preventative maintenance can reduce the risk of filter-related driveability problems. Most vehicle manufacturers, however, no longer specify a replacement interval for the fuel filter. Or, if they do it's some incredibly long interval like once every five years or 50,000 miles. Many mechanics feel this is unrealistic. Waiting that long to change the filter is asking for trouble, especially if you drive on gravel or dirt roads, buy the cheapest gas you can find from "cut-rate" stations, use gas with alcohol in it, or your vehicle is more than six or seven years old and may have rust in the tank. 

The fuel filter on carbureted engines is usually located at the inlet fitting of the carburetor, or an "in-line" filter is used between the fuel pump and carburetor. 

When replacing a filter that screws into the inlet fitting on the carburetor, be careful not to
over tighten the filter. The threads in the carburetor are relatively soft and can be easily stripped. But also make sure the filter is snug so that it doesn't leak. It's okay to apply some gasket sealer to the filter threads to assure a leak-free connection. But do not use RTV silicone sealer (which gasoline dissolves) or teflon tape (pieces of which can flake loose and end up in the carburetor). 

When replacing an in-line filter, most filters come with two new rubber hoses that go on either side of the filter. Use them. Don't reuse the old hoses because rubber hoses deteriorate over time and can leak or shed small flakes or rubber that can end up in the filter or carburetor. Also, make sure the hose clamps are properly positioned and tight. 

Replacing an in-line fuel filter -  

NOTE: Most in-line filters have an arrow showing the direction fuel should flow through the filter. Install the filter so the arrow points toward the carburetor. 

FUEL INJECTION FILTERS 

Fuel filters on fuel injected engines are usually larger and have a finer filter element than those on carbureted engines. Consequently, they are usually more expensive. 

The filter may be located anywhere between the fuel tank and injector fuel supply rail or throttle body. On many cars, light trucks and minivans, the filter is located underneath the vehicle along a frame rail. On some, the filter is part of the electric fuel pump assembly inside the fuel tank! Refer to a shop manual for your fuel filter's location. 

CAUTION: Fuel injected engines usually have a lot of residual pressure in the fuel line, even when a vehicle has sat overnight. So either follow the manufacturer's recommended procedure for relieving pressure in the line prior to removing the filter (applying vacuum to the fuel pressure regulator manifold fitting, or cranking the engine with the ignition disabled), or wrap a rag around the hose connections and slowly loosen them. 

If the filter has an arrow indicating the direction of flow, it should be installed with the arrow pointing toward the engine and away from the fuel tank. 

If the filter is located inside the tank, the tank will probably have to be removed. Follow the same precautions as previously described for replacing a plugged pickup screen. 
 

 ENGINE STARTS THEN DIES

Answer:

It sounds like the classic symptom of an exhaust blockage, probably due to a clogged catalytic converter. The converter can overheat and be damaged if excessive amounts of unburned fuel enter the exhaust system. This can happen if the engine has one or more fouled spark plugs or leaky exhaust valves. When this unburned fuel hits the converter, it sends temperatures soaring. The ceramic substrate or pellets that support the catalyst can melt and partially or completely block the flow of exhaust through the converter. 

If a complete blockage occurs, the engine will start normally but the exhaust has no place to go. Backpressure quickly builds up and within a couple of minutes the engine quits running. Eventually, the pressure will seep out and allow the engine to restart after it has sit for some time. But the blockage will prevent it from running for long. 

The cure here would be to replace the converter. But first, the underlying problem that caused the converter to overheat and fail needs to be diagnosed and corrected -- otherwise the new converter will suffer the same fate. 

Other possible causes of this kind of condition include a crushed exhaust pipe, some prankster shoving a potato up your tailpipe, a collapsed inner wall in a double-walled head pipe, or a muffler that's obstructed with rust debris. 
 

 ELECTRIC COOLING FAN

Answer:

Yes. The cooling fan is only needed when engine temperature rises above a predetermined level --or when there is an increased load placed on the cooling system (as when running your air conditioner). The rest of the time, running the fan would be a waste of electrical energy so it is turned off. 

Electric cooling fans are found on most front-wheel drive vehicles with transverse mounted engines as well as many late model rear-wheel drive vehicles. Electric fans are used on FWD cars because the fan doesn't require a belt drive and can be mounted independent of the engine's location. What's more, electric fans require less power to operate (for improved fuel economy and performance), they're quieter, and they allow more precise control over cooling. 

By comparison, a mechanical belt-driven fan can require anywhere from 5 to 15 horsepower depending on engine speed and the size of the fan. Even with a fan clutch to reduce the drag at higher speeds, it's still a lot of wasted power. 

FAN OPERATION 

At highway speeds, there is usually enough airflow through the radiator that a fan isn't needed. So the fan usually only operates when the vehicle is sitting in traffic or driving at slower speeds. 

On older applications, the electric fan is controlled by a temperature switch located in the radiator or engine. When the temperature of the coolant exceeds the switch's rating (typically 195 to 235 degrees F), the switch closes and energizes a relay that supplies voltage to run the fan. The fan then continues to run until the coolant temperature drops back below the opening point of the switch. Most electric fans are also wired to come on when the A/C is on. Many vehicles also have a separate fan for the A/C condenser (dual fan systems). One or both fans come on when the A/C is on. 

In newer vehicles with computerized engine controls, fan operation is regulated by the engine control module. Input from the coolant sensor, and in many cases the vehicle speed sensor too, is used to determine when the fan needs to be on. 

CAUTION: Many electric fans are wired to come on anytime the engine is above a certain
temperature, regardless of whether the engine is running or not. This means the fan may come on after the engine has been shut off. So keep your fingers away from the fan at all times unless the battery or fan motor wires have been disconnected. 

CHECKING THE FAN 

Four things can prevent a fan from coming on when it should: a bad temperature switch or coolant sensor (or problem in the switch or sensor wiring circuit); a bad fan relay; a wiring problem (blown fuse, loose or corroded connector, shorts, opens, etc.); or a failure of the fan motor itself. Only the latter would require replacing the fan motor. 

One way to check the operation of the fan motor is to jump it directly to the battery. If it spins, the motor is good, and the problem is elsewhere in the wiring or control circuit. Another check is to test for voltage with a voltmeter or test light at the fan's wiring connector. There should be voltage when the engine is hot and when the A/C is on.