Lean Misfires at 2700-2800 rpm - Page 6 - 3000GT/Stealth International Message Center

TurboBob · 10-25-2006, 06:21 PM

Quote:

Originally Posted by badass3000

............... I am pretty sure that somehow a malfuntioning LT1 mass burnt a hole in my ECU fuel map @ 2700rpm.

You're kidding, right?

badass3000 · 10-25-2006, 07:32 PM

yeah, i know thats somewhat impossible but thats what everything is pointing to.
ECU1 + LT1 = bad
ECU2 + LT1 = bad
ECU1 - LT1 = bad but better
ECU3 - LT1 = good
(ECU2&3 are known goods)

what else could it be?

TurboBob · 10-25-2006, 07:41 PM

Quote:

Originally Posted by badass3000

yeah, i know thats somewhat impossible but thats what everything is pointing to.
ECU1 + LT1 = bad
ECU2 + LT1 = bad
ECU1 - LT1 = bad but better
ECU3 - LT1 = good
(ECU2&3 are known goods)

what else could it be?

The common denominator is the LT1, and your ECU could be flaky as well.

That said, the blow thru configuration can be challenging to tune due to all sorts of swirly effects (throttle blade angle, BOV stuff, non-laminar flow, and plain ordinary turbulence). That and 2700-ish is where the ECU switches to open loop at part-medium throttle.

Got a log of that operating point?

Bob

badass3000 · 10-27-2006, 06:00 PM

running speed density now, spent 4 hrs on the dyno today and problem could not be ironed out.
Bad ECU.
Bob, can you fix or trade? Plus I want higher rev limiter

TurboBob · 10-27-2006, 06:15 PM

there is nothing I can do to fix an ECU other than replacing the caps. I don't have any of the other parts......

I can take a look, but I don't think I can do much for it.

Did you swap in another ECU to verify that it is bad?

I can handle the rev limit stuff whenever you want.

Bob

badass3000 · 10-27-2006, 06:22 PM

yes..........

Quote:

Originally Posted by badass3000

Tried a known good ECU yesterday and it didnt studder/backfire at all.
BUT the funny thing is that I did the swap in the afternoon and was driving all morning and the car was mostly well behaved with my ECU. I could get a slight studder/backfire if I tryed but it was slight. Today driving around with my ECU the stumbling was very strong.
So im not possitive but 99% sure my ecu is messed up, even though I changed caps a year ago and all was fine since then. I am pretty sure that somehow a malfuntioning LT1 mass burnt a hole in my ECU fuel map @ 2700rpm.

DoctorDex · 11-10-2006, 01:35 PM

I got off the phone today with AvPro and they don't think the problem is caused by the ECU. I'm not sure what to do now. The problem seems to be getting worse and it the affected rpm range seems to be spreading, it now misfires between 2400 - 3200 rpm.

It doesn't appear to a closed loop to open loop issue, because if I'm driving in a low enough gear in closed loop, above 3200 rpm and below 2400 it runs like a champ. If I go WOT ~ 2000rpm and accelerate in open loop it still wants to stutter in the 2400rpm - 3200rpm range, its just not as noticeable.

Has anyone done an EGR blockoff and encountered this problem? I'm curious as to whether or not these symptoms could be caused by a leaking/poorly functioning EGR valve?

I had previously disconnected my EGR valve, so it would stay in the "closed mode" all the time. However, I noticed when I'd boost, I was seeing an extremely lean rear bank. It turns out boost was spilling into my exhaust through the EGR pipe. I cleaned the EGR valve and did another run at WOT, it was still leaking into the exhaust. The problem was only cured when I reconnected the EGR valve. However, since the EGR valve is acting so screwy I think I'm going to get a rid of the thing all together. Maybe this will help cure the high (7 - 10) counts (x5-6 times) I see from time to time, when gradually accelerating.

Declan

badass3000 · 11-10-2006, 02:14 PM

my EGR has been gone for years.

DoctorDex · 11-10-2006, 02:20 PM

Well, there goes that theory.

DoctorDex · 11-15-2006, 12:52 PM

I've put my car in storage now for the winter. While driving it on the highway to the storage place I couldn't even use 5th gear because this would bring me into the 2600-3200 rpm range that causes the missing.

When I would drive in 5th, it'd miss and I'd hear the bov blow off ever so slightly. If I stayed at that RPM point it'd miss constantly (or pulse) and I'd hear a chuff-chuff-chuff kind of sound from the bov. This made me wonder if it could be an issue, like Keithmac said earlier on re: pressure pulses.

An experiment I would have like to have tried (but ran out of time), would be to use of a blowthrough MAF setup and drive very slow, so as not to overspool the turbos, with the turbo piping disconnected from the Y-pipe. Without the turbos connected to the Y-pipe there would be no possibility of pressure pulsing and if it still missed in/around 2600-3200rpm then it would effectively rule in/out pressure pulsing as a cause of the problem. Has anyone tried this?

10-25-2006, 07:32 PM	#52 (permalink)
badass3000 Wanted: Traction Problems Join Date: Nov 2002 Location: Jacksonville, Fl Drives: one "badass" VR4 Trader Rating: (18)	Re: Lean Misfires at 2700-2800 rpm yeah, i know thats somewhat impossible but thats what everything is pointing to. ECU1 + LT1 = bad ECU2 + LT1 = bad ECU1 - LT1 = bad but better ECU3 - LT1 = good (ECU2&3 are known goods) what else could it be?

10-27-2006, 06:00 PM	#54 (permalink)
badass3000 Wanted: Traction Problems Join Date: Nov 2002 Location: Jacksonville, Fl Drives: one "badass" VR4 Trader Rating: (18)	Re: Lean Misfires at 2700-2800 rpm running speed density now, spent 4 hrs on the dyno today and problem could not be ironed out. Bad ECU. Bob, can you fix or trade? Plus I want higher rev limiter

10-27-2006, 06:15 PM	#55 (permalink)
TurboBob Resident mad scientist Join Date: Jan 2003 Location: Near Detroit Drives: 86 GN 91 RT/TT Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm there is nothing I can do to fix an ECU other than replacing the caps. I don't have any of the other parts...... I can take a look, but I don't think I can do much for it. Did you swap in another ECU to verify that it is bad? I can handle the rev limit stuff whenever you want. Bob

11-10-2006, 01:35 PM	#57 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Saskatoon, SK Drives: '91 VR4 Trader Rating: (13)	Re: Lean Misfires at 2400-3200 rpm I got off the phone today with AvPro and they don't think the problem is caused by the ECU. I'm not sure what to do now. The problem seems to be getting worse and it the affected rpm range seems to be spreading, it now misfires between 2400 - 3200 rpm. It doesn't appear to a closed loop to open loop issue, because if I'm driving in a low enough gear in closed loop, above 3200 rpm and below 2400 it runs like a champ. If I go WOT ~ 2000rpm and accelerate in open loop it still wants to stutter in the 2400rpm - 3200rpm range, its just not as noticeable. Has anyone done an EGR blockoff and encountered this problem? I'm curious as to whether or not these symptoms could be caused by a leaking/poorly functioning EGR valve? I had previously disconnected my EGR valve, so it would stay in the "closed mode" all the time. However, I noticed when I'd boost, I was seeing an extremely lean rear bank. It turns out boost was spilling into my exhaust through the EGR pipe. I cleaned the EGR valve and did another run at WOT, it was still leaking into the exhaust. The problem was only cured when I reconnected the EGR valve. However, since the EGR valve is acting so screwy I think I'm going to get a rid of the thing all together. Maybe this will help cure the high (7 - 10) counts (x5-6 times) I see from time to time, when gradually accelerating. Declan __________________ '91 VR4 - Modlist: DR650R Turbos, Snow Stage 2D Alky Kit, DSM SMICs, blowthrough ported LT1 MAS, Dejon Tool intakes & y-pipe, Blitz DSBC Spec R, HKS SSQV BOV, PTE 580cc injectors, Aeromotive FPR & Filter, Hotwired Supra Pump, ek2mfg fuel loop & spacer, HKS DLI, MSD Wires, Apex'i S-AFC II, MAFTranslator, Turbobob ECU, Scanmaster III, LC-1 WBO2, ESP Downpipe, Vac/EGR delete, Gutted Precats and Test pipe, Maximal Solid F/R motor mounts, 300m 18 spline output shaft, Centerforce Dual Friction Clutch, RPS Flywheel, Powerslot slotted rotors, Goodridge SS Brake lines, Hawk Pads (front), Stillen Metal Matrix Pads (rear)

11-10-2006, 02:14 PM	#58 (permalink)
badass3000 Wanted: Traction Problems Join Date: Nov 2002 Location: Jacksonville, Fl Drives: one "badass" VR4 Trader Rating: (18)	Re: Lean Misfires at 2700-2800 rpm my EGR has been gone for years.

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11-10-2006, 02:20 PM	#59 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Saskatoon, SK Drives: '91 VR4 Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm Well, there goes that theory.

11-15-2006, 12:52 PM	#60 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Saskatoon, SK Drives: '91 VR4 Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm I've put my car in storage now for the winter. While driving it on the highway to the storage place I couldn't even use 5th gear because this would bring me into the 2600-3200 rpm range that causes the missing. When I would drive in 5th, it'd miss and I'd hear the bov blow off ever so slightly. If I stayed at that RPM point it'd miss constantly (or pulse) and I'd hear a chuff-chuff-chuff kind of sound from the bov. This made me wonder if it could be an issue, like Keithmac said earlier on re: pressure pulses. An experiment I would have like to have tried (but ran out of time), would be to use of a blowthrough MAF setup and drive very slow, so as not to overspool the turbos, with the turbo piping disconnected from the Y-pipe. Without the turbos connected to the Y-pipe there would be no possibility of pressure pulsing and if it still missed in/around 2600-3200rpm then it would effectively rule in/out pressure pulsing as a cause of the problem. Has anyone tried this?