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3000GT TT misfire running rough

Curtisphillips

Probationary Member
1
0
Oct 22, 2018
Yelm, Washington
Hi, I have a 1993 Mitsubishi GTO imported from Japan, its the same as the 3000gt. The car is a vr4, 5 speed manual, twin turbo. When I start the car it runs super rough and the rpms change alot. First thing I did was change the spark plugs and do a compression test. Compression is about 170-175 in all 6 cylinders. After changing the spark plugs the car ran exactly the same. Then I started checking the coils. I can unplug 2 of them while the car is running and it makes no difference in idle. So i would assume the coils are the issue but then after reading other people were saying that it could still be the ptu, ecu, an injector, etc. Does anyone know what my next step should be? The engine is a 6g72. I don't want to just start throwing parts at it, I would rather perform a couple other tests to narrow it down more. I did check the coils with a multimeter and they all read the same and are within spec.
 

1990TSIAWDTALON

Moderator
8,339
4,220
Nov 14, 2013
Independence, Kansas
If all the coils test the same I would assume they are good. Try swapping them around to make sure. The ptu would be the next "suspect". I don't know how to test the 6 cylinder ptu but bet its not much different then a 4g63's ignition.
 

steve

DSM Wiseman
13,911
962
Feb 3, 2002
Boulder, Colorado
The 3S platform is notorious for loosing the signal for the third coil (Cyl 3 & 6) due to capacitor leakage damage of the ECU. Make sure there are no signs of leakage or corrosion to the ECU PCB before you invest much time or money in this project.
 

Sp1kE

Proven Member
374
15
Dec 24, 2005
stratford, ON_Canada
The 3S platform is notorious for loosing the signal for the third coil (Cyl 3 & 6) due to capacitor leakage damage of the ECU. Make sure there are no signs of leakage or corrosion to the ECU PCB before you invest much time or money in this project.

+1
 

brian9397gsx

Proven Member
1,559
93
Apr 28, 2008
sioux city, Iowa
Swap the coil with another in the pack and see if it follows the coil or stays with the same cylinders. If there's no change check your continuity on that signal wire back to the pcm. If there's continuity than load test the wire with a test lamp if that passes then yeah you're looking at a pcm issue with that driver.
 
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