3000GT/Stealth International Message Center - View Single Post - Lean Misfires at 2700-2800 rpm

DoctorDex · 10-07-2006, 05:10 PM

Initially, I thought this problem was due to an exhaust leak on the front bank, because when I pulled the DP a few weeks back, I noticed that my rear exhaust manifold was white (lean) and my front was black (rich). However, I'm starting to wonder if its something else.

Today, I drove home to visit the parents and while doing some short WOT pulls, I noticed that I was getting, what looks like, heavy spark blow out on my rear bank. My rear O2 voltages were dipping as low as 0.60V, @WOT, in between 4600 - 6000 rpm and then it would start to knock.

At WOT, despite the voltages being as low as they were, I couldn't feel/hear any spark blow out and the voltages weren't bouncing around like they do with spark blow out.

In addition to the above mentioned issue, I still have the lean misfires anywhere below 3000rpm, but it is definitely worse between 2700-2800rpm. Contrary to what I thought before, it doesn't seem to make much difference, if I'm in closed loop or open loop, so long as I'm under 3000rpm it wants to miss.

Does this sound like spark blow out? Or it could it be an exhaust leak? Could it be bad wires, or does it sound like something else?

At the moment, I'm running ngk iridiums gapped to .028, new stock coils, NGK resistor wires, @ 17.5 psi of boost.

I'm almost at my wits end with this problem and _any_ help would be greatly appreciated.

Thanks.

Declan

10-07-2006, 05:10 PM	#19 (permalink)
DoctorDex Forum Member Join Date: Jul 2005 Location: Edmonton, AB Drives: '91 VR4 - RIP Trader Rating: (13)	Re: Lean Misfires at 2700-2800 rpm Initially, I thought this problem was due to an exhaust leak on the front bank, because when I pulled the DP a few weeks back, I noticed that my rear exhaust manifold was white (lean) and my front was black (rich). However, I'm starting to wonder if its something else. Today, I drove home to visit the parents and while doing some short WOT pulls, I noticed that I was getting, what looks like, heavy spark blow out on my rear bank. My rear O2 voltages were dipping as low as 0.60V, @WOT, in between 4600 - 6000 rpm and then it would start to knock. At WOT, despite the voltages being as low as they were, I couldn't feel/hear any spark blow out and the voltages weren't bouncing around like they do with spark blow out. In addition to the above mentioned issue, I still have the lean misfires anywhere below 3000rpm, but it is definitely worse between 2700-2800rpm. Contrary to what I thought before, it doesn't seem to make much difference, if I'm in closed loop or open loop, so long as I'm under 3000rpm it wants to miss. Does this sound like spark blow out? Or it could it be an exhaust leak? Could it be bad wires, or does it sound like something else? At the moment, I'm running ngk iridiums gapped to .028, new stock coils, NGK resistor wires, @ 17.5 psi of boost. I'm almost at my wits end with this problem and _any_ help would be greatly appreciated. Thanks. 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, Dual feed fuel system with Aeromotive FPR & filter, Hotwired Supra pump, ek2mfg plenum 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 mounts, 300m 18 spline output shaft, Centerforce Dual Friction clutch, RPS flywheel, GC coilover conversions with helper springs, Powerslot slotted rotors, Goodridge SS brake lines, Hawk pads (front), Stillen metal matrix pads (rear)