Random intermittent missfire

Greetings and thanks for your attention. The subject vehicle is a 1992 Dodge Stealth, 3.0 V6, DOHC 24 valve (Mitsubishi made I believe), manual trans, 117k miles. It has an intermittent but persistent electrical miss that effecte all cyclinders according to my timing light. It is there immediately upon cold startup and when warm as well; it is present throughout the RPM range and frequently stalls when idling. The Check Engine Light is not lit, but is functional.

Any ideas as to the cause, or methods to further diagnose the source of the trouble?



The engine management system in your vehicle is the OBDI system. The OBDI systems did not monitor engine misfires. So if the engine is misfiring the Check Engine light won’t come on.

From what you describe the first thing to suspect is the secondary ignition system. This includes the coil, distributor cap, rotor, plug wires, and spark plugs. If any of these components have worn out, it can cause multiple misfires.


Thanks Tester. This is a distributorless system, and the miss seems to be more severe than dropping a single cylinder; I think it is losing the entire spark to all cylinders at once for several revolutions at a time, then switching back on. I am suspecting the crankshaft sensor or ECU, but would like to determine the problem before throwing expensive parts at it. Can I backprobe the crank sensor with a voltmeter to look for a consistent pattern or voltage? Are there any other components I have not thought of which are likely to cause a total loss of spark like that?

Found the problem. Mice had nested in the air intake box and chewed a hole through the air filter. I suspect this was the cause of failure in the mass airflow sensor. I cleaned it twice, but still it would not run right with the MAF plugged in; replacement with a rebuilt unit and a new air filter has it running well again.

How did the use of your timing light lead you down the wrong path? How were you expecting your timing light to work and how was it actually working? You can help other readers if you explain.

I would not say the timing light lead me wrong, it just did not point me directly to the problem. It did tell me that the engine was losing spark intrmittently; I just did not think the MAF would cause that; I wrongly thought it would affect fuel mixture but not spark production. Live & learn.