91 3000GT VR4 Overfueling Problem - 3000GT/Stealth International Message Center
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Old 02-04-2010, 01:32 AM   #1 (permalink)
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Default 91 3000GT VR4 Overfueling Problem

I have a 91 Twin Turbo with an over fueling problem. The engine was rebuilt a little over a year ago and ran for several thousand miles. Roasted the Tranny and the car sat for around a year without being run. Got the Tranny back together and upgraded with hardened shafts. Drove the car about 30 miles and it went through half a tank of fuel. I also noticed fuel in the crank case. Changed oil and started looking for problems. The only thing that I can think is one of the injectors varnished over and got stuck open. So far the symptoms are: Car Idles fine. Under load there is extremely high boost on the gauge but no power. When the car returns to idle after running, the exhaust shows black soot from over fueling and the car wants to stall. Boost returns to normal. There is no check engine light.

I have not pulled the injectors, nor do I have an Oscilloscope to check injector pulse width. I verified the fuel pressure regulator control as functional, but not the fuel pressure regulator. All injectors ohm out fine. The car is currently stock for electronics. All vacuum lines check out for correct placement. I am planning on switching out the Fuel Pressure Regulator later this week to one with a pressure gauge to verify correct fuel pressure.

Any insight would be greatly appreciated.

James
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Old 02-04-2010, 03:33 AM   #2 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

This could be caused by a massive boost leak. Pressure test first. If no leak is found then look for load based problems.

The MAF sensor determines load. Since your problem seems to be load based I'd go there next. You said the car idles fine but shows the incorrect boost reading under load. The guage may not be faulty, the signal coming from the MAF sensor may be incorrect causing the ECU to think there is a high load and injecting more fuel for the higher load. Good luck.

Jeff
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Old 02-04-2010, 09:53 AM   #3 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

That was one of my original thoughts. I removed the MAF and cleaned it. I used alcohol and q tips. There was no change. After reading other posts, would it be possible to run the car with the MAF removed? I performed to diagnostic as outlined in the Mitsubishi service manual and it checked out. If I cannot run the engine with the MAF removed, whats to best way to replace the MAF, should I go with the GM Conversion, or some other setup? I am still going to work on the FPR this weekend, I hope.
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Old 02-04-2010, 10:28 AM   #4 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

Did you pressure test the system?

Jeff
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Old 02-04-2010, 11:23 AM   #5 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

Jeff,

I have not pressure tested the system yet. I have been debating on the best way to do that. Any advice, tips, trick etc. Thanks for the help.

James
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Old 02-04-2010, 10:58 PM   #6 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

3sx sells an adaptor for the oval where the MAF sensor is. It has a pneumatic nipple on it already and this works great. Apply air pressure and work your way around the intake plumbing feeling and listening for air leaks. You could also do a search as some other members on the board have marketed their own testers. I believe Rob Beck makes them as well.

Jeff
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Old 02-05-2010, 12:34 AM   #7 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

kinda wonder if your problem isnt the opposite, your fuel filters are probably clogged (said it sat for a year) causing your car to try and run rich thus your no power on load. If your injector was stuck open, very rare situation you would probably notice on startup. Does your car start quickly?
or plugs, they are constantly cleaned from the car running
Sitting is probably the worst scenario for a car
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Old 02-05-2010, 02:26 AM   #8 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

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Originally Posted by 93stealthman View Post
kinda wonder if your problem isnt the opposite, your fuel filters are probably clogged (said it sat for a year) causing your car to try and run rich thus your no power on load. If your injector was stuck open, very rare situation you would probably notice on startup. Does your car start quickly?
or plugs, they are constantly cleaned from the car running
Sitting is probably the worst scenario for a car
I seriously doubt that. Fuel filter clogged will simply cause a lack of fuel from the restriction to fuel flow. The loss of power would be present but the dumping fuel, I doubt.

Jeff
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Old 02-05-2010, 09:22 AM   #9 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

imagine if you where the car computer and saw a situation of lacking fuel flow, what would you do? The answer is try and shoot allot more fuel. That factory boost gauge is load controlled, so with high injector pulsewiths you would think he would have some power.
ecu s can only respond to inputs, and usually in the opposite manner in which the inputs are read. ECU can be a very accurate computer until a situation where an input is out of its range. then the computer does everything in its little stored memory to save the engine, like Dump fuel, pull timing...
black could be a bad turbine wheel seal, fact is the car is not in front of you to diagnose.
you can only go off the information someone gives you who is having car troubles...

Its just an idea that no one else thought of, he obviously went for what he thought the problem is. Doesnt hurt to think out of the conventional sometimes. It is a cheap filter and defiantly wont hurt his performance ...

Last edited by 93stealthman; 02-05-2010 at 09:45 AM.
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Old 02-05-2010, 11:21 AM   #10 (permalink)
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Default Re: 91 3000GT VR4 Overfueling Problem

In closed loop fuel control the O2's are providing the feedback for the ecu to know what the mixture is so even if it decided to DUMP fuel, the closed loop control would correct the situation.

A faulty turbine seal should blow a blueish colored smoke. Black smoke is fuel and the fact that the OP stated that it's fuel throws this idea out the window.

I'm not trying to be rude, I'm just stating facts. You are right the car isn't in front of me, but if it was for these symptoms, fuel filter and turbine seal would not be a high priority on my things to check list. A pressure test hasn't been done yet and that should find a large portion of his problem if not fix it completely. At idle the car runs fine and the boost leak becomes a vacuum leak and maybe not a large enough vacuum leak for the fuel trims to raise a red flag. Under boost just the opposite happens and metered air is forced out holes in the intake and ipw's are given for the air that was metered not for the air that shot out the intake. and you have a dumping fuel under load condition which will produce black smoke, cause lack of power(overly rich mixture), fuel in the crankcase, and horrible fuel economy.

The fact that the car was recently put back together tells me everything that was reinstalled after the tranny fix needs to be looked at closely.

Jeff
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