Okay I give up, my 1994 MGM has run rough or is missing ever since I filled up with gas in Colorado Springs on a trip. I happened right after I filled up so 1st thought was bad gas so I went through that tank of gas and replaced the fuel filter, had the sytem treated and the injectors and TB flushed and cleaned out. It still runs rough and backfires in the TB. I replaced the Mass Airflow Sensor prior to this problem which fixed the hard start and poor running and cleared the check engine light. We read the error codes and had one for the the Throttle positioning sensor and I replaced that. I checked the plugs the are all fresh and I replaced one of the coil packs... Still running rough, I bought the car recently and it only had 68K on it now it has 73,000. It ran GREAT after I replaced the MAS for about 2 weeks. What should I check or replace next, any ideas??[img]smileys/smiley6.gif[/img]

 

I think it has happened because of some bad gas which have affected your engine.

 

you can get all the injectors checked for free at a autozone if there is one near you. Check out any parts store to do it fot you. i think it is one of two things. A different coil or even the new one. and it is probably dirty injectors. the only way to clean injectors is to take them off and to have them ultrasound cleaned.

 

Sorry, i ment to say get the coils checked for free....not the injectors.





You either have a bad coil and a bad injector. try pulling off a spark plug wire for each cylinder wile it is running. if it stays the same when that one is pulled off, then it is probably the bad one. the motor should run worse when a wire is pulled off. this might help you narrow down the bad and good ones sometimes

 

sometimes you can also pull off the injector harness on each injector when it is running. like the coils, it should run worse when pulled off. it it runs the same then you have a bad injector. If no luck then it could still mean that they are dirty. this is probably what is going on. summer fuel is cheaper and more dirty then winter fuel

 

I think the altitude in Col. may have messed with your computer telling it to richen and lean the fuel mixture. TPS sounds like the culprit but you say you changed it. Did you reset the computer?

 

Hi guys, thanks for the responses.. I live at 7000 ft. so I don''t think the alt was/is a problem. I did have the fuel system/injectors flushed there in CO Springs after it happened. I have reset the computer several times-when I replaced the MAS, TPS and the coil.


The fuel injector suggestion sounds good and I will try that next. Mostof the shops arouond here want ~$100 just to hook it up to their computer for diagnosis'' and of course they want to make more $ off the repairs so please keep the suggestions coming and I will update you with the fuel injector update.


Thanks again!

 

For a lean/rich fuel mix... it is not affected. the computer will adjust this several times a day. changing altitudes does not perm. affect the computer. It is programed to change. there is no need to reset the computer for this suggestion

 

How many miles on the plugs? make sure that a plug was not affected when you went through higher altitudes. the computer would not be affected, but if it ws needing a tune up and it was running rich for 30 seconds, then it is possible that a plug was fouled out when the computer compensated for the altitude. The computer is fine. It is the plug, coil or injector. i am 90% sure of this

 

when you said you checked the plugs.. How? did you just look at them or did you check them with a tester? you need to see if the plugs are sparking. a clean plug can still mean that it is fouled out. see ifit is getting the proper spark. most likely if it is not then you would then check the coil for the amount of spark and resistence. a new coil does not mean it is working properly. most aftermarket coils are junk anyway. you need to check these with a meter at least and not check them offf the list becasue they are new or look good.