Ignition Timing Problems

Ignition timing specifications are configured to promote the most complete combustion possible in a specific engine with a specific compression ratio and cubic inches of air displacement. Fuel under these conditions will ignite and burn at a constant rate. The manufacturer suggests that the fuel is ignited by a spark plug with a specific amount of degrees before top dead center on the compression stroke.

With the fuel burning at a constant rate, if it were ignited at top dead center of the power stroke, it would not have time to burn completely by the end of the stroke. The fix for this is to ignite it a little earlier so part of the fuel mixture is burnt by the time the piston reaches top dead center on the power stroke. This gives more time to burn and a more efficient fuel burn.

Now as the engine speeds up there is less and less time for the fuel to remain in the cylinder. It will not burn faster, so the timing must be advanced more to give it a "head start" so to speak, to maintain the same efficiency.

If the timing is not advanced enough, a major power loss results. The unburned fuel enters the converter, overheats the converter and destroys it. The oxygen sensor brings the check engine light on. The plugs and the valves carbon up quickly. There is a major dead spot when accelerating, to mention just a few of the problems.

If the timing is too far advanced, the fuel will be exhausted prior to the end of the stroke, resulting again in a lack of horsepower, a rough running engine and a quick cylinder head temperature buildup. A too-advanced situation will cause detonation within the cylinder, causing damage to the valves, head gasket and rods. On late model vehicles with fuel injection, the timing is not adjustable. On some foreign models that still have a distributor, it is possible to adjust the timing.

The crankshaft sensor sends a pulse signal to the ignition control module. The module takes this pulse and transforms it into a digital signal and sends the signal to the PCM computer. The computer in turn takes this digital signal, references the rest of the sensors' signals and makes a decision on the amount of timing necessary give the particular circumstances. It then sends an ignition signal to the ignition control module as to how much advance is necessary and when to fire the coil.

Given this information, the problems are within the system with the exception of a vehicle with a distributor, which can be adjusted.  The crankshaft sensor is responsible for indicating top dead center on the number one cylinder. A bad connection, worn or failed sensor or one that has the wrong air gap will cause major problems with timing.

A bad coolant temperature sensor or thermostat will cause and engine temperature change seen by the computer, which in turn responds by changing the timing. A knock sensor, which is responsible for sensing detonation within the cylinder, if bad, will also cause the computer to retard the timing to prevent the detonation. The intake air temperature sensor can cause a timing problem if it fails. The timing depends on whether it fails in the high or low range.

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