I've had a bad stumbling problem, and it misfires at idle all the way in the power band. ALso, it does it really bad in high gear under load, buck likes a mule. Here is what I have done:

-replaced plugs, ran car still stumbled
-replaced wires, ran car, still stumbled
-replaced 02 sensors, ran car, still stumbled
-replaced OPTI, coil, and ICM, ran car, still stumbles the same

what else is there to do??? I'm thinking time to start fuel pressure checks but I doubt that it will cause stumbling like this, even at idle?!

Also the car is OBDII, no codes.
ALso the knock retard jumps up to as much as 15 degrees when the car stumbles, could a bad knock sensor/module cause stumbling??

Also, the PCM was sent to MADZ28 to reduce knock sensitivity, this reduced some of the knock but still stumbles.


Brian

 

Replace your fuel filter. Check fuel pressure. Check compression (maybe you have a blown head gasket) Other than that all i can think of is your ECU. Maybe one of the capacitors is leaking, which can happen.

 

I've replaced my fuel filter about 2 years ago, I guess thats a while. I'll have to get a fuel pressure guage then and do a check on the fuel pressure and replace the filter if I have to. I also put in some fuel injector cleaner that didn't help either.

Compression check, I never did one of those before I'll have to look into what I need to do one and if a local shop can do it for me.

THanks, anyone else ever had my problem, is there any engine sensors that could cause this?? I have a scanmaster, any parameters I should look for??

Brian

 

The injector cleaner tends to break sediments loose in your fuel tanks and lines. Maybe a piece brokeloose and cloggoed up one of your injectors. Start the engine and let it idle then pull off each injector wire and replacing noting a change in rpm. A V8 will run almost perfect with 1 cylcinder out, so if you an injector thats flooding your cylinder it will shut it off. Since you have a scan tool, run the injector test. You should be able to individuall shut off each injector and it will record a change in rpm and the injector cycles. are you running rich or anything?

 

Also a mis-adjsuted rocker could cause it, or collapsed lifter.

 

Try the ECM sensor for the coolant temp on the front of the water pump. I chased a stumble for about 2 months on a customer car, only to have it be this $7 sensor !

-Shannon

 

happened to me to , i replaced all my ignition components and it turned out ot be my fuel pump,. (my problem is teh pressure test came out fine b/c teh pump was only doing it spontaniously then just died)
thats just somthing else to look at and whate everone else sugested

 

Check for leaks in your intake track. A tear in the intake track will allow unmetered air (MAF can't see it) into the intake and cause you to run lean. What color were the spark plugs when you changed them and did all eight look the same? Also verify that there isn't any arcing occuring naround your wires; even though you changed them, they may require some dielectric grease to inhibit arcing.

 

The ECT seems to be fine, the temp guage reads perfect in the dash.

The plugs that I pulled out were normal colored; the car seems to not be running too rich or lean.

I put in the fuel injector cleaner after the problem started, so this should not have caused the problem.

I sat down and talked to a few people and here is a list of what we think to check next, how does this sound and any comments or anything to add??

1. Disconnect MAF, run speed density
2. Disable knock sensor
3. check cat
4. check fuel pressure
5. check injectors
6. vacuum check
7. pull valve covers check lifters/springs
8. compression check
9. PCM

Thanks
Brian

 

Oh I also replaced the PCV valve, still no change.


I'm going to record some o2 data to see if the car is running lean/rich, I'm not to sure on how to read it all that well so I'll post them if you guys could take a look for me.

Thanks again

 

not that this helps ya but i have about the same prob. Not so much a miss at idle but sometimes its major under a load or wot. I mean my car has chirped the tires 3 times in first gear it stumbled and jumped so bad. I replaced all you did including the ecu,knock sensor, did a compression check, new fuel pump, etc... I have not checnged the coolant temp sensor? I would have never thought that would have caused a problem like this. so i guess im saying good luck.

 

The ECT for the PCM is not the one for the gage. The gage uses one and the PCM uses another.

Did you check the items on your list yet?

If you still have a cat, that's where I'de put my money. Do a back pressure test of the exhaust system or simply unhook it at the headers.

If that's ok, do a leak down test of the cylinders.

Check the valve springs for a weak one.

 

didn't know that, worth a try though.

I took the car for a ride last night, it actually is running better then it has in a long time, maybe the computer needs to adjust to the new stuff I put in?? ANyway, there is hope we'll see

 

pull ech plug wire and see which one is missing...go from there

 

What about the EGR?


Rob

94 Z28 A4