faskend

Engine won't start. Sometimes fires but won't run and occasionally misfires which would cause me to suspect the timing belt. I have tested/checked the following: 1) fuel pump is OK, not sure of fuel pressure but greater than 15psi, 2) changed fuel filter, 3)timing belt is OK and timing is OK, 4) crankshaft sensor reads 350 ohms and gives out pulses when turning over motor, 5) cam shaft sensor reads 350 ohms and gives out pulses when turning over motor, 6) spark is intermittent if at all and very weak. Is the spark supposed to be strong arcing like or just a weak blue spark?, 7) installed new plugs but made no difference. Showed black carbon on 1 & 4 cylinder plugs after trying to start and no sign of firing on 2 & 3, 8)coil measures .8 ohms on both coil primaries and 13.5k ohms on both secondaries. I have tried checking the ignition coil by applying 12V to primary with 2 plugs hooked up the same as if installed in engine. Spark is very weak and usually will only jump one plug. I know that spark is generated when primary coil is opened but need to know if PCM sends multiple pulses for each firing event to properly check coil.
Even when I make and break primary coil rapidly the spark is very weak. I am using a 12V source to energize primary. Both coils have the same characteristics which leads me to believe that it OK and my checking methodology is not correct.

I am reluctant to try another PCM module as the cost is very high if it doesn't solve the problem. Any Ideas would be greatly appreciated.

 

backlash1

HI
Have you tried a known-good coil, be it a new one or from a similar car that runs ok ? Measuring resistance on a coil can be very misleading, even when they show up ok they could have cracks that would cause the spark to leak or come out blueish and weak like you describe. This kind of spark will be good enough to jump a gap outside but not strong enough to work inside a combustion chamber under high pressures and temperatures. The spark from a good coil wil be almost white. I wouldn't worry about the PCM just yet. Regarding your question, most modern cars fire not only on compression but also on the exhaust stroke to reduce emissions, and so the coil will receive its signals accordingly. Hope this helps.

marc