CEL Code Not Right? Symptoms dont match?

[Drew1287]

Ok since I got the charger on the car I have run into a problem thats stumping me and I dont wanna do anything else till I get this sorted out. The car ran fine for about 100miles then the CEL came on with a #1cyl misfire. I checked out the plug and the gap was wrong, since I corrected that I havent had that problem again. Now I keep getting 172 and 175 for banks 1&2 too rich. When that light comes on the car starts to bog, miss, and pop when at rpms under 1500. The plugs when pulled look clean, almost to the point of looking lean. I reset the ECU and it comes back on when sitting at idle. I dont know what would be cause it since I didnt do anything to the stock fuel system besides adding the FMU. The code never came on b4 the charger and with it missing makes it almost impossible to pull into traffic. What you guys think is causing it?

 

[Drew1287]

Only 6 Views?

 

[fiveofanatic]

Bypass the FMU & see what happens?

 

[Drew1287]

If the plugs looked rich thats what I would do, but they look lean!

 

[fiveofanatic]

Well, the code says the engine is too rich, right? I'd bypass the FMU just to eliminate it as a possible cause, then start looking elsewhere. Is the MAF aftermarket? It could be the culprit also.

I wish I had my AllData here at home; at work I can get good in-depth code info.

 

[GTblack_00]

how old are you o2's ?? might not be working correctly anymore, also take off fmu and have it dyno tuned, check for maf contamination(filter oil).

 

[Drew1287]

Wouldnt running the car with the supercharger and no FMU cause MAJOR problems? I should clean the MAF sensor but it is the stock one. Also The o2s look original, but I have a O/R hpipe. I cant figure this crap out?

 

[fiveofanatic]

It'll only cause problems if you get into boost; it'll run normally otherwise. The stock maf probably eliminates it as the problem, but it could be dirty or contaminated with K&N oil if equipped & you've oiled it recently.

 

[Sam98]

It sounds like your fuel pressure is too high at idle and the PCM is trying to lean it out. I had the same thing happen to me and the plugs didn't show any evidence of it, but mine was definitely too rich. You may have to go get it tuned to eliminate the problem. O2 sensors could cause similar problems, but it isn't very likely that both of them went out at the same time (still possible though). Another possibility is the MAF...

 

[Drew1287]

I dont have a fuel pressure guage but thats what seems to be happening. It ran so good for a while and then started doing this. I am rather confised with how its acting. I need to have it tuned, but theres so much more I wanted to do till then!

 

[Sam98]

I dont have a fuel pressure guage but thats what seems to be happening. It ran so good for a while and then started doing this. I am rather confised with how its acting. I need to have it tuned, but theres so much more I wanted to do till then!

With an FMU you need a fuel pressure gauge because FMUs are not particularly reliable. Without a means of monitoring your fuel pressure, you could lean out under boost without knowing it and burn a hole in a piston. I finally got rid of my FMU because I couldn't quite get the AF right with it, and it would occasionally stop working without warning.

 

[Drew1287]

I took out the a/f guage that does absolutly nothing and put in a nordoskg fuel pressure gauge. I will start watching pressures. Anyone have any numbers I should be seeing?

 

[Sam98]

Stock fuel pressure is 39 psi, but will be a little higher with the FMU (about 45 psi). After that it depends on the FMU, but typical would be an additional 8-10 psi per pound of boost above 4.

 

[Drew1287]

I am running a 12:1 disc in the FMU right now, With the 3.6 inch pully I am only seeimg 5psi of boost at 5500 and spikes near 7 for the last 500rpms which is useless. I am ordering the 3.33 to get this thing to around 10psi I hope.

 

[Sam98]

I am running a 12:1 disc in the FMU right now, With the 3.6 inch pully I am only seeimg 5psi of boost at 5500 and spikes near 7 for the last 500rpms which is useless. I am ordering the 3.33 to get this thing to around 10psi I hope.

Then your fuel pressure should sit at 48 psi through 4 lbs boost, then go up another 12 psi/lb of boost. The engine vacuum may or may not lower your fuel pressure as I have 1 FMU that does and another that doesn't...

 

[Drew1287]

Pressure at idle is 39psi, and when the boost spikes 7 , the guage reaches around 52psi ....