Here's the symptoms: For a while I was having occasional stumbling under part throttle, out of boost. At full throttle there was no issue. Then on a particular day I was running it pretty hard, followed by about 5 miles of gentle driving, staying out of boost, shifting at 3000. Left her running for 5 minutes to cool down; shut off. The next time I started it up, there was no extra fuel under boost any more—running really lean. The FPR has been checked and the vaccuum lines are in place and in tact. Does this sound like a fuel pump issue? I've also read up on here that some people bypass the solenoid for that vaccuum line and run it straight from the LIM to the FPR; could the 'noid be the problem?

93, twin-turbo boosting to 17psi peak, M2 Intake, engine rebuilt by Atkin's Rotory about 2500 miles ago.

Thanks in advance for whatever ideas you guys have.

 

What kind of ECU do you have?

 

That's a hell of a lot of boost for the stock twins to handle. Also, when was the last time your fuel filter was changed?

 

Stock ECU. I realize that should be overload for it, but there was a time, just after I bought it, where I had no fueling issues, even at peak boost. That seemed to say to me that it could handle it, if just barely. The reason I'd tend to blame something else in this case is because this is a change from prior circumstances.

GoodFella - Not sure actually, that's a good idea to check. Probably will do tomorrow.

Any other suggestions are welcome.

 

If you are running the stock ECU without remapping you are lucky to still have your motor. Also you prob hit fuel cut and are in limp mode.

 

Yeah, you're deff lucky to still have a running motor right now. Get a Power FC asap before something worse happens.

 

Any further info on limp mode? Hadn't heard of that.

 

Fuel cut won't throw the car into limp mode, it will just basically kill fuel and make it feel like the car seizes up for a minute.

You said "there was no extra fuel under boost any more—running really lean", how exactly did you determine this?

 

Mahjik - As I would rev higher, it wasn't making any more power and it would push to maybe 2 or 3 lbs. of boost and then drop off to zero. The engine shuddered a bit.

Aside from this, I pulled the ECU codes and came up with IAT open or short circuit, both Full and Narrow Range Throttle sensor open/short, and the Idle Speed Control Solenoid open/short. That leads me to believe that, at least on the specific throttle related ones, it wasn't reading throttle position correctly and therefore wasn't fueling correctly for the intake charge. Anyone make better heads or tails of those codes?

 

It sounds like you have a wiring issue. The IAT code will definitely make the car run like crap. You probably are in limp mode, but not from fuel cut, from some of those codes.

How old is the wiring harness?

 

How are you running 17psi on the stock computer when it cuts fuel off at these points?
RPM - ABS. CUT OFF(PSI) - SEA LEVEL CUT OFF(PSI)

1000 - 26.5 - 11.8
1500 - 26.5 - 11.8
2000 - 26.5 - 11.8
2500 - 26.5 - 11.8
3000 - 26.9 - 12.2
3500 - 27.1 - 12.4
4000 - 27.5 - 12.8
4500 - 28.0 - 13.3
5000 - 26.9 - 12.2
5500 - 26.0 - 11.3
6000 - 25.8 - 11.1
6500 - 25.4 - 10.7
7000 - 25.4 - 10.7

 

I assume that with the IAT...if you aren't getting a code, then there is no reaseon to believe there is an issue with it, correct?

 

I am getting the IAT code. That's 11—the first code that pulled.

93ttwankel - Not sure honestly. I'd never seen those numbers myself. I assume stock ECU, but am actually unsure. Those figures would lead us to believe it's something other than stock now wouldn't they? Investigation will occur.

 

still curious about this..

 

He said he's getting code 11, that is the IAT.