Hey, well i'm new to the forum, but i'm definetly not new to cars, and infact i have 2 3000GT's, BUT my 91 3000GT VR-4 is giving me a fit, and i'm about tired of messing with it. It has 54,500 miles on it, i've had it since May, 06. It started out great when i first got it, but now it's got a problem. When the car cranks It's absolutely fine, but after it get's warmed up, it will randomly miss around 3K-4k RPM's, I have replaced plugs, wires, coils, fuel filter, and For some reason that i'm not sure of but the ECU was rebuilt at 48,000 miles, so basically it was done right before i bought it. it has all new belts, the guy put a couple grand into it before i bought it, so i thought it was a sound investment, but it looks as though it's gonna be a money pit over something stupid. The way i see it, is that it can't be real major because it just does it randomly, not constantly, but it WILL do it everytime it get's drove. Also, it will miss at idle after it get's warm, and the RPM's will generally drop to like 600, and you can hear and feel the miss, because it kinda makes the car shudder. Also, it's only done this a few times, but it would Bounce up and down in the RPM's after cranking it, while it's hot, and the bounce goes from 1k Rpm's and drops to 100, and jumps back up, and you have to stab the throttle a couple times to get it to straighten it out. I have talked to 3SX Performance, but I don't want to let them keep it and go through it for $70 dollars an hour, because the Labor on just pin pointing the problem will cost more than the part, and the labor to install it, i think. So.. If anyone could PLEASE help me with any information on this Issue, It would be greatly appreciated! I love my 3000GT's and The VR-4 was my dream car, but i'm afraid it's gonna turn into a nightmare.

 

maybe a bad MAF?

 

The capacitors inside the ECU tend to leak esp on the 1st Gen models. Even though the PO said it was rebuilt, try removing the ECUto take a look inside. There are 3 capacitors you should inspect very carefully and make sure that (A) there is no leakage around or beneath them and (B) that they were actually replaced. If they haven't been replaced,replace them ASAP. It's not a matter of IF theoriginal CAPS will leak, it's a matter of WHEN they will leak.
My 92 VR4 had intermittant no start issues and also had an intermittanttach bounce before i bought it. I already knew it was an ECU causing the no start concerns which is what gave me leverage in negotiating a lowball price on it. Anyway- i removed and installed new caps on the PC board and it solved BOTH problems. Either way, the tach bounce is likely ECU or PTU related as they are pretty much the only circuits related to the ignition tach signal. Either one can cause a random misfire .

Joel, CA

 

To Sebba: I am thinking that maybe that the MAF is the culprit because, for some reason the MAF has been torn into, and the only reason i know this is that there is some wierd looking calk/glue around the gap were the cap of it would come out. BUT, i didn't notice that before i bought it, because i was too excited about the car.

And to Joel: the Person i bought the car from actually didn't tell me the ECU had been rebuilt, the Receipt for the work was in the glove box, and it was "supposedly" done at Jeff Phillips mitsubishi in Hickory, NC. But because i know that dealerships are also crook's (i've not had good experiences with them), I am going to check the capacitors. Also What is the PTU? I am generally good with the abbreviations, but i can't thinkin of what that would be.

AH.. i just thought of something else, This not a problem with the car, but I installed an aftermarket boost gauge, and i've hooked it up like 3 or 4 diferrent ways, and I can't get that stupid thing to read accurately, it's all over the Place, Which is the best vac. hose to hook it to? and then if i have it hooked like that, could it just be a cheap/defective gauge, because it will read from 9-11 lbs. fairly stable in 4 and 5 but WOT in 1-3 it read up to 9-11 but shakes and falls back down to 5, i don't get it.

 

This may be a mechanical problem and not an electronics problem. Remove your valve covers and check for damage between the cams and the valve stems. Make sure you check the springs. I would also do a compression test to see if you are losing any compression through the valve or valve seat.

 

Caulk around the MAF is a good sign that someone installed a CAI and did a sloppy job.

 

to ICTPonder: The car was completely bone stock when i bought it, except for some weird wiring to an Alarm system. ButI don't know, i mean the previous owners could have done anything to it, and just put it back stock, but supposedly both other owners were 50+ years old, and As for a CAI, i've not seen one for the Twin Turbo.

 

I mean i haven't seen a true CAI for it, i have installed an open element filter on it though!

 

Replacing the capacitors isn't a type of repair that the dealership would normally perform.Generally,the dealership would only sell a brand new OEM ECU.If the customer agrees,they wouldalso sell an entirely "rebuilt" ecu with no implied warranty from the dealer. Even with that, i'd still take a look inside.
PTU = Power Transistor Unit - located just beneath the ignition coils.

J

 

alright, well i guess i'll go ahead and order one, because i mean it's 16 years old anyway, it probably wouldn't hurt to freshen up the electronics anyway. But Thanks for the help everyone, i really didin't expect to get this much info this fast! also, if this would help with any info, I have installed a Turbo Timer, Blitz Super Sound BOV, i did the "free Boost Mod" from stealth316.com, and the open element intake filter, although i wouldn't think that any of that would have anything to do with my car doing that stuff.