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Engine running rough, Serious electrical issues NEED HELP ASAP

2K views 17 replies 5 participants last post by  kspinazzola 
#1 · (Edited)
1996 3000GT SL DOHC

Engine running rough and need help diagnosing

Well heres the story, bought my purple 96 SL about a month ago knowing it had a couple issues, when i bought it it ran and drove ok, but i got it for cheap cuz the owner couldnt figure out one issue, The motor wont rev past 3000 RPM, very weird, almost feels like it has a rev limiter, it just wont go past (this limit varys slightly, sometimes as low as 2800 RPM but ive gotten it up to 4K a few times)
anyway, one day im driving, and the engine dies on me out of nowhere, so i pull over, engine starts but only for a second at a time before dying again, by time its towed home its a crank no start. Spray starter fluid in throttle body, starts for a second, dies again, so i give it a fuel pump and filter. after a lot of BS putting the thing in and redoing all the fittings, I finally get the pump going and seems to be getting its 14 Volts all the time now, (New MFI and fuel pump relay too) so now the motor will finally start.

Now heres the issue, im suddenly having tons of issues,
Idle is very rough, if i dont keep tapping the throttle every once in a while it will stall, (Very weird tho, if i take the intake off the throttle body it seems to be better, idle right at 800-900 and never stalls. so idk what thats about)
Also if i try to drive it, it makes very little power and stalls very easy, could barely make it down the street before I pushed it back.

So i finally brought it to my mechanic to have the check engine codes scanned and he says there are a bunch of codes, he listed the MAF airflow sensor, crank sensor, and something about an idle control motor? idk i know i replaced my idle airflow valve just a few weeks ago cuz it was throwing a code for that.

So, we have rough idle, stalling, no power, and wont rev past 3000 RPM
How can i diagnose this? is my ECU going bad? or is it realistic that all those sensor just suddenly stopped working? maybe over the course of the couple weeks it wasn't running? maybe the fuel pump wasn't to blame after all? it was due for replacement tho so whatever. My mechanic doesn't even wanna touch it with all this stuff, Please help!!!!!!!

Also I wanna mention, when I try to start the car it often just clicks and doesnt crank, I have to try over and over until it decides to crank, clicking sounds like its coming from way down in my started motor kinda area, I know this is a somewhat common problem but now that all this stuff is happening its kinda on and off so idk what that's about

Also I should probably mention, previous owner claims the motor was rebuilt, and has new heads, not sure if this is even true (didnt see any paperwork) but the engine itself looks pretty good and heads and intake manifold are painted, also the cam gears and pulleys all look pretty new, maybe a few thousand miles old.

Any help is greatly appreciated, this car is my daily driver (Stupid me)
and i need it back on the road ASAP ASAP ASAP


**** UPDATE

Put a new ecu in because the shop I brought the car to said the ecu was fried.
New ecu changed nothing but I have a couple new symptoms

Car will not shut off when I take the key out, the lights and stuff will but the engine keeps running...
The guage showing batters voltage stays around 14-15ish instead of 12 now.
No idea what this means but I hope you guys will have some ideas.
Thank you
 
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#2 ·
Definitely open up your ecu and check it out. Super easy to do and worth it. Some of the symptoms you listed are definitely indicative of a bad maf. Instead of taking the whole intake pipe off just unplug the maf and take it for a short drive to see if it gets better. I wouldn't leave it like that though.

If you haven't already I would also take the time to check the cam timing since you said it seems the gears are new.

Also look up click click no start for a fix to your starting issues. Its apparently a common issue but I don't know much about it.
 
#4 ·
I started it up with the mass airflow disconnected and it ran much better, idle at about 800 than slowly dropped to about 750, seemed good, authought when I tried to rev it up a little (just to about 1500) to listen to it, it didn't really wanna rev, unless I went very slowly,
Does this mean the MAF sensor is bad?
When I started it with the sensor connected it still ran pretty rough
 
#3 ·
You drove the car daily when it was running like that?!? poor car.... the abuse from some owners.. ):
 
#5 ·
havent been daily driving it, only brought it home from the previous owners house then to work a couple times (I work at a dealership) to get it looked at
Since then ive been having to get rides to and from work, and I really need to get this car running right so it can be my daily driver
Until recently I had a Mitsubishi Raider durocross to drive, but no longer own that truck
 
#11 ·
Yeah check timing marks @ TDC, get a new or tested IAC and adjust the basic idle, I've noticed that if the TPS is really bad it will throw some injectors, did you have a code for those? Check your MAF wiring, there is a test for every item in the FSM, then you know the basics.. fuel pressure, injectors, spark, plugs..
 
#12 · (Edited)
I just brought it to a new me mechanic today who will look through it, but the cam timing looked ok to me, I will have them check tho, that tps would explain some issues and when I look it the connector is kinda loose and looks like one of the little clips to hold it on is broken or something, I just know it's pretty loose so maybe that connection is weak and causing problems. I will ask them to look at it and see if that's the cause
 
#13 ·
SO here's the latest update, the shop says it was definitely the ECU, now I can get a new one (it says new but I believe it's a remanufactured one but idc) for about $100
Or I can have one ordered and installed by the guys at the shop for about $375, seems a little high but they say the upside to that is they can try to figure out what caused the ecu to go bad and try to prevent it from happeneing again, I think it might have just been the ecus time (leaking caps maybe?)
So knowing this should I just get one online and put it in myself? Or do you guys think it's likely I'll run into problems and should have the shop do it?
 
#17 ·
Im not to worried about the parts, the ecu doesn't seem to expensive, reconditioned/ remanufactured ones all over the place, and I'll get a warranted with the part, the thing I'm worried about having a short circuit somewhere and shorting out the new ECU as soon as I put it in.
 
#18 ·
OK, so here's the latest update, got the ECU in the mail, and headed over to the shop where my car was parked, and I immediately noticed something, the mechanic had told me over the phone that it was the ECU that was not working, but the carpeted panel that covers the ECU was still in place and the ECU was in the car, so the mechanics had clearly not even looked directly at the old ECU, at that point I figured with my luck the new ECU would do nothing. So I disconnected the battery and put the new one in, and of course, no change.

Except for one thing..... now then I go to turn off the engine, it will not turn off when I pull out the key.... WTF??? I have to pull the maf or another sensor to stall the motor for it to turn off. I honestly have no idea what this means, so any help would be appreciated.
 
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