Cadillac Repair: backfiring & missing, little birdy, electrical problem


Question
I have a 1990 Cadillac with 140000 miles on it, I had it in the shop for 5 months and they can't find the problem, I even took it to the dealer but all they could do was tell me pretty much most of what the other garage did, it was too costly for the dealer to continue. The problem is the car backfires and miss badly, but not all the time, it seems to be worst at night when I turn the headlights on, The garage where I went said it was the disturter, and they rebuild it, it worked for 10 days then it slowly started to go back the way it was. It backfires so bad it has blowen out two mufflers. Can you help please, this has been going on for over 6 months.

Answer
It's NOT that your problem CANNOT be diagnosed, It is that they do not want to take the time to do the diagnostics and or they lack expertise.

If you had the distributor rebuilt, I would like to know EXACTLY why it needed to be rebuilt. If it worked OK for 10 days then I would highly suspect an electrical problem with the distributor wiring from the ECM (computer) to the distributor or possibly a mechanical problem with the distributor gear that engages into the camshaft gear whereas the camshaft gear may be extremly worn causing to much movement between both gears.

There IS another probability where you said that it is worse at night when the headlights are ON. Since ANY LOAD such as headlights when activated require the alternator to produce more amperage output to keep the battery charged this LOAD is also sensed by the computer to advance the timing of the ignition to the spark plugs.

Without actually having the vehicle myself, I can only give you the above GENERAL possibilities.

I wish I had an EXACT cause to give you but not having access to the vehicle It is impossible to say without performing time consuming tests.

Although I do NOT recommend USED parts and since you said that it was OK for 10 days AFTER they rebuilt the distributor, Has a little birdy telling me that your problem is more than likely within the distributor and or the distributor gear.

IF you can obtain a used distributor, install it and see if your problem is cured for a few days and IF it returns after a few days I would suspect that the gear on the camshaft is worn which is causing the distributor bushings to wear very quickly thus causing sideways movement of the distributor shaft.

It is FIXABLE if you can find someone who will take the time and has the expertise to diagnose it correctly.

EXACTLY what was ALL replaced when the distributor was rebuilt ?.

What previous work of any kind has been performed on the vehicle prior to this problem ?.


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