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Old 10-03-2007, 10:59 AM   #524 (permalink)
UCSB VR4
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Join Date: Jan 2003
Location: San Jose, CA
Drives: 1992 3000GT VR4
Trader Rating: (1)
UCSB VR4 is an unknown quantity at this point
Default Re: Lean Misfires at 2700-2800 rpm

Quote:
Originally Posted by TurboBob View Post
do the ECU reset again, but unplug your O2 sensors so the trims can't learn.

See if that changes the re-occurrance of the symptom.

Bob
This ABSOLUTELY did the trick for me, except I unplugged the O2s without resetting the ECU (just to record any changes before/after resetting the ECU). Now, my car drives like an absolute champ, so I'm not even going to bother resetting the ECU... the idle RPM doesn't fluctuate up/down/up/down, the acceleration is smooth through the entire RPM band, and when letting off the gas in neutral the rpms step down controllably instead of bottoming out at 300-400 RPM (almost stalling the engine).

I don't suppose there are any ramifications to unplugging the O2s beyond freezing your fuel trims (which actually improves performance on my car). The only thing is that my ARM guage is practically useless now, but what a small price to pay, I never used it anyways.

I actually enjoyed driving to work today, the problem is gone.

- Jeff

EDIT: I wanted to also mention that the BRAND NEW ECU I swapped in had no effect on this problem, prior to the fix implemented above.
__________________
1992 RED 3000gt VR4:
Air:
DR 650s, DSM SMICs w/ 1 3/4" piping, hard pipe kit upgrade & 2 pre-turbo (no-maf) pipes w/ filters, GReddy Type-S BOV (open loop).
Fuel:
MAFT-PRO v5.03 (SD mode w/ Electronic Boost & Timing Control, GM 3 BAR MAP Sensor, GM IAT Sensor, & Innovate LC-1 wideband O2), Supra fuel pump (hotwired), 550cc PTE injectors @ 45 base psi.
Ignition:
Magnecore KV85-R100 spark plug wires, Denso iridium IK27 spark plugs, Odyssey PC925 battery.
Engine:
.03" Overbore, 2nd-gen Lifters, polished heads.
Exhaust:
Gutted precats, ATR 3" downpipe, 3'' Test Pipe, ATR 3" catback.
Drivetrain:
RPS 6-puck disk, RPS lightweight flywheel, 3sx lightweight drive pulley, polyurethane motor mounts, stillen drilled and slotted rotors, 18x9.5 5Zigen FN01RC rims, BF-Goodrich KDW-2 tires, Cusco rear strut bar.
Miscellaneous:
Corbeau seats, short throw shifter, presidential alarm system, 8 inch bazooka tube, kenwood double-din deck, 300lbs of miscellaneous weight reductions... "who's your daddy?" license plate
Future Mods:
1 Piece PST CFDS
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