Grand Marquis Driving Me Crazy!


#1

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


#2

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


#3

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.)


#4

you could have cloged cats


#5

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


#6

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.


#7

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…


#8

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


#9

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


#10

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’.