[moswald80]

Hey Guys,

I wanted to see if any of you had any ideas about a hesitation problem I am having. First the mods:

FPGreen, 3" Inlet, 8 cm Hotside
APS 70mm CAI and APS Turbo Inlet (I recalibrated my Intake Calibration Map)
Deatschwerks 740cc Injectors and Walbro
Aquamist (Running 50/50 Water/Meth) (Although the hesitation I am getting is at low RPM/Throttle/Load where the meth isn't spraying)
TGV Deletes
Cobb Catted Downpipe and Borla Catback
StreetTuner

The hesitation/stuttering occurs right around 2400 - 2800 RPM and seems to be worse at lower throttle positions. After logging (sorry I don't have a log I can post here at work) I saw that the hesitation is due to running very lean in that RPM range (like 15-17 AFR on the LC-1). My first guess was the O2 sensor was going bad but after logging that it seemed to correspond very well with the wideband. Also, the short-term fuel trims are usually pegged at 25% during the hesitation (indicating the ECU knows it is running lean) however, the long-term trims are actually slightly negative in that area (indicating that it often runs rich at that MAF Voltage: around 2.5 -2.6 V).

I cleaned my MAF (before the APS CAI I had been running a K&N Drop-in) and the hesitation seemed to get a little better but I am still getting that lean area. I have tried adding some Tip-in Enrichment but it didn't make much difference. Also, I will get the hesitation even if I go through that RPM range at constant throttle.

I am thinking it has something to do with the transition to Open Loop or possibly the infamous FIBTE Table (which I haven't messed with yet, but I do have a Tactrix Cable. Can anybody explain what that table does?).

Any Ideas? Is there something I should log that would give you a better idea of what's going on? Please don't hesitate to ask any questions you may have as I may have left something out of my explanation.

Thanks,

Mike

[Black-STi]

I have basically the same mods as you except I have PE850s and I have the exact issue you have, stumble right around 2500-3000rpm in every gear...I've read its due to low IPW of the larger injectors

[moswald80]

Well, it's nice to know I'm not the only one. I think if the problem was low IPW then we would have problems at lower RPM's (and idle) too. Have you adjusted your FIBTE table at all? I have been planning to try changing that but I don't really understand what it does. I've just read that it should be adjusted when you get bigger injectors.

Wolfplayer, you haven't run into this with your bigger injectors and the 70mm CAI?

[crystal_Imprezav]

Well one thing that I noticed off the bat would be what you stated as the MAF voltage where you see this occur. Typically around 2.5v would be the transition into openloop, which would point me to ask you what you closed loop calibrations are? A stutter can be caused by a variety of factors including but not limited to boost control, fuel, or timing. But since you said you fuel ratios are swinging lean, that could eliminate timing. It could also have something to do with AVCS. I would need to see a log or the map to comment more. There are too many ways that the car could stutter for me to pin point it.

[R4ND0M_AX3]

sounds like the same problem I had
Lean stumble

I ended up changing my injector scaler and delays.

[moswald80]

I am running the Deatschwerks 740cc Injectors. I changed the Scaler based on Christian's Spreadsheet (I think it was 3630). I didn't think I should change the latency values since they are basically modified stockers. If anybody else has these injectors, what values are you running for your Scaler and Latencies?

Thanks,

Mike