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Discussion Starter · #1 ·
My 1995 3000GT SL has a pretty bad misfire going through cylinders 3&6, and I’ve done as much as I can to try and fix it so far, yet nothings helped. I’ve replaced the spark plugs and gapped them correctly, I’ve replaced the spark plug wires, the ignition coils, the PTU and I’ve had the fuel injectors checked as well. The previous owner had a few wiring diagrams of the wiring for the ignition coils printed out and left them in the glove box, so I think that could be where my problem is. Any ideas on how to fix?
 

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93 NA ATX 3000gt DOHC
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Little clarification needed, does both 3&6 cylinders miss constantly or does only one of the two miss at a time?

If the 3-6 coil is not firing either cylinder, then there’s few possibilities.

First if the ground trigger wire from coil pack connector to PTU pin 11 (yellow hi-light below) has rubbed thru insulation at any point enough to make intermittent ground to body metal, it will cause misfire of 3-6 coil because of incorrect timing of ground leg normally controlled by ECU & PTU. Note: wire color leaving coil pack connector for 3-6 coil is Blue wire w/yellow stripe (L-Y) and runs to remote tach connector at A-16 and leaves that connector as a Black wire w/white stripe (B-W) back to PTU pin 11, so it could happen anywhere in that path where wire bundles come in close contact to body/drive-train metal.

Second if prints are correct there’s two wires running to A-16 connector (above from previous Note:) from ’94 and up cars, if corrosion has developed where those two wires are clamped together in single wire end connector, that could cause dropping of ground when it shouldn’t be, also causing misfire. That A-16 connector is the blue plastic test connector of the three between battery box and wiper motor. See second picture.

Third ECU capacitor problems could cause erratic firing on a ignition coils.



 

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Discussion Starter · #3 ·
Little clarification needed, does both 3&6 cylinders miss constantly or does only one of the two miss at a time?

If the 3-6 coil is not firing either cylinder, then there’s few possibilities.

First if the ground trigger wire from coil pack connector to PTU pin 11 (yellow hi-light below) has rubbed thru insulation at any point enough to make intermittent ground to body metal, it will cause misfire of 3-6 coil because of incorrect timing of ground leg normally controlled by ECU & PTU. Note: wire color leaving coil pack connector for 3-6 coil is Blue wire w/yellow stripe (L-Y) and runs to remote tach connector at A-16 and leaves that connector as a Black wire w/white stripe (B-W) back to PTU pin 11, so it could happen anywhere in that path where wire bundles come in close contact to body/drive-train metal.

Second if prints are correct there’s two wires running to A-16 connector (above from previous Note:) from ’94 and up cars, if corrosion has developed where those two wires are clamped together in single wire end connector, that could cause dropping of ground when it shouldn’t be, also causing misfire. That A-16 connector is the blue plastic test connector of the three between battery box and wiper motor. See second picture.

Third ECU capacitor problems could cause erratic firing on a ignition coils.

View attachment 307468

View attachment 307470
Thank you! I’ll have to check it out when I get the chance. But yes it is both 3&6 which do not fire at all if I’m correct, so hopefully this’ll give me some insight.
 

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you can find the above mentioned wiring cluster fuck 6-10" back down the loom from the end of the coil/ptu wires what i did is cut the 4 wire mess apart then i just spliced the black/white wire to the blue/ yellow wire and left the other 2 that run back down the loom out of the mix its been golden ever since
 

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you can find the above mentioned wiring cluster fuck 6-10" back down the loom from the end of the coil/ptu wires what i did is cut the 4 wire mess apart then i just spliced the black/white wire to the blue/ yellow wire and left the other 2 that run back down the loom out of the mix its been golden ever since
@HOSS, Yours might be a 1st gen car that had a splice (junction) in wire bundle where you indicate, with single Black/white wire leaving that splice point of the Blue/yellow wire and going to A-16 tach test connector near wiper motor and the Blue/yellow wire continuing from splice onto PTU pin11. While 2nd gen and up electrical prints doesn't show the splice point, but instead the Blue/yellow wire running all the way to A-16 tach test connector where it's then crimped together with a Black/white wire that then runs back to PTU pin 11. This could easily cause confusion in 2nd gen cars, because there's also a larger Black/white (power wire) that goes to pin 6 of PTU.
 
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