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Grand Marquis Driving Me Crazy!

1994 Misses/Backfires



Okay, to start out I have a 1994 Grand Marquis with 115k that misses/backfires



At 100k it had a slight miss when cold so I replaced the plugs/wires with generic autozone set (the miss was a little better)



At about 112k I replaced the MAF sensor and the car ran beautifully for about 2 months and now runs horribly, I have already tried another MAF sensor and that is not the problem



I have also replaced the air filter, thermostat, and the DPFE sensor (and here is where it gets weird) My car had a December of 1993 build date and I had to use the DPFE sensor from a 1993 since the 1994 was totally different from the one on my car



This car misses/sputters/backfires/chugs whenever I put it under load, rather I am accelerating from a stop or accelerating to pass and it doesn’t matter if it’s warm, cold, hot, lukewarm, whatever



I am at my wits end, my gas mileage is now terrible and I am afraid to pull into traffic with all of the hesitation/sputtering misfiring…PLEASE HELP! I am at my wits end

Knowing the trouble codes can help a lot to find what’s wrong. This article should help: http://www.autozone.com/shopping/repairGuide.htm?pageId=0900c152801e49dc

I agree with Hellokit completely. His advice should be the first step.

The only thing I will add is that if you use an analog VOM or simple code reader it would be a good idea to read the directions closely and become familiar with the process first. It’s not difficult at all; just a bit confusing at first if you’ve never done it.

(And if you hear the engine RPMs run up during a KEY ON/ENGINE RUNNING test this is entirely normal. They’ll drop back when it’s through testing.)

you could have cloged cats

Any way to test the catalytic converters, heat shields are off on one side and half off on the other

The easiest way to check for clogged cats is with a vacuum gauge.
If you’re unsure about the use of a vac. gauge post back and I’ll tell you what to look for. Sometimes the instructions with a new gauge can be misleading or incomplete when testing for this condition.

All of this miss-firing should cause the CEL (check engine light) to come on…Has the light ever come on?? It sounds like a bad coil. You have two I think, one on the front of each bank of cylinders…other things to check for: Low fuel pressure, EGR valve stuck open when accelerating, dirty injectors…

There are two coil packs, each with two coils - four coils total, but only two assemblies to replace.

Thanks for the suggestions, I am going to have Autozone run the codes tomorrow, the only code that previously showed up was low voltage to the egr

Your car has OBD I. Auto Zone may test cars which have OBD II. They, usually, won’t do OBD I. They may have an OBD I Ford tester you can buy; or, you could use the ignition key method of pulling the code (through flashes).
Anyhow, bring the codes here for cussin’ and discussin’.