Chris Lockhart

Will try to check the MAF this weekend John. As well as LH ECU.

Mark no problem. Hey you're in here trying to help me, and I appreciate the heck out of it.

One thing I just remembered as strange yesterday was when I pulled the fuel rail cap off there was no pressure on it. Only got a few drops out of it while installing the fuel press gauge. I thought that this was kind of odd, but the car had not been run in 4-5 hours at that point. Not sure how long it's supposed to hold pressure. I checked it last night before bed, and it was still holding at around 58 psi, approximately 1 hour after being run. I'm still wondering if it might not be a fuel flow problem. It's obvious that I have pressure, but I wonder about flow. The surging sure reminds me of an old carburated car with a clogged fuel filter.

blau928

Have you ever changed the in-tank filter...?

Chris Lockhart

In tank filter????

Didn't know there was such a beast Richard. Please tell me more!!!! p/n, pics, etc..... TIA,

blau928

Chris,

I would have to dig out a receipt in my pile in the house to get the part number. It would be easier for you to call any of the big 3, and they will be able to give it to you in 1 minute or less. I think I bought mine from Devek about 1-2 years ago..

Anyway, if you drop the tank cover under the car, then look for the hose that feeds the fuel pump from the tank. The protrusion from the tank is actually a filter that screws into the tank. It is a bit of a pain to change, as you need to drain the tank to get it out. If you have never changed it, it may be a good chance it is the culprit.. It is only a few $$, and well worth it..

No pixx in the office of it, but if you drop the tank cover, you will see what I am talikng about..

Hope that helps..

Chris Lockhart

Richard, best as I can tell from what you've told me, it won't help, as there are model year differences. Where you are speaking of the filter being installed, is where I have a second fuel pump on my GT. From my talk with DR at 928 Specialists yesterday, I just have the main fuel filter behind the external pump. I guess the other model years that only have the external pump have the in-tank filter that you're speaking of. Thanks anyway though. I appreciate all input.

blau928

You're Welcome..

Chris Lockhart

Got it figured out thanks to my wife!!!!!!!!! She drove the GT to the store today, and noticed something that I had not. I have an Arm-1 narrow band air/fuel ratio meter installed in the ashtray. She noticed that the LED lights were stationary in the center (yellow) position. The lights normally cycle back and forth from lean to rich as the sensor "hunts" after the o2 level. I went out and checked a few items, then decided to see what would happen if I disconnected the o2 sensor connector. Disconnected it, went out for a drive, and WOW my baby's back!!!!!!!!!!!!!!!!!!!!!!! I have my old but functional sensor to run temporarily, until I can get a new one from Jeannie.

Thanks to all who helped me out with wonderful support and advice!!!!!!!!!!!!! You guys are the best!!!!!!!!!!!!!!!!!!!!!!

the flyin' scotsman

Well done to the SO.............sometimes all it takes is a another set of eyes to see the obvious.

Chris.........did you have other symptoms before the car behaved this badly or was it a sudden event?

Chris Lockhart

Malcolm, it started acting up very mildly about 2 weeks before total failure. To another driver, it probably wouldn't have been noticed, but you know how things are with your own car. You have the feel, and know when something is amiss, even if it's mild. I originally thought it was plugs, and replaced them. Didn't help, and it slowly got worse, until it became virtually undriveable. I'm just glad it was minor. Take it easy,

MarkRobinson

My suggestion was ruled out so quickly, I dont think anyone read the obvious:

"Because of all this extra fuel, the surging you're feeling is your O2 frantically trying to pull out injector pulse to compensate for the extra fuel pressure, so you're feeling the extreme rich/lean conditions on the motor, which makes it surge, even while driving. I've had this on 3 of my '85-86 cars since AA's chips allow too much injector pulsewidth at closed-loop, low rpm driving. Most of this surging is felt when holding the throttle steady at 1500-2200rpm (on my car). Because of your extreme fuel pressure, I imagine this is what's happening."

You were feeling the surging, which is also caused by a failing O2 sensor (slowing of response). Sorry I didn't mention that symptom as well...you can only juggle so many thoughts in your head at one time. Although, with such high fuel pressure as you Rennlisters are running on your S4's, the O2 is working over (probably) it's entire range to get the correction necessary for adequate AF's in closed loop. I wouldn't expect it to last as long as an S4 with normal fuel pressure. Glad you found it!

mark

MarkRobinson

For what it's worth, on my past 951 with a AF meter installed, I had a "weak ground", which caused voltage feedback to the computer, making my car run like crap. I won't make that mistake again!

mark

Chris Lockhart

You're dead on Mark. I did discount what you were saying because I had tunnel vision on the fuel pressure isse. Didn't let the o2 side of what you said sink in, and you were correct. Thanks for your help. It is MUCH appreciated!!!!!!