Why is this happening?

Tiny
BLACK3KBEAUTY97
  • MEMBER
  • 1997 MITSUBISHI 3000GT
  • 188,000 MILES
I have a 97 3000GT, it has 190000 miles on it. With cylinder 3 spark plug plugged in halfway itll run normal and has a slight misfire, but when I plug it in like it should be its pretty bad. It wont stay running long enough to even back outta my driveway. Ive replaced everything that has to deal with the ignition except the distributor cap, I dont wanna replace things that wont fix it. I cant deal with the crap any longer its been going on for about 6 months now and im pulling my hair out cause of it. If anyone can help me diagnose this problem it would be greatly appreciated.
Friday, January 13th, 2012 AT 3:05 PM

13 Replies

Tiny
KHLOW2008
  • MECHANIC
  • 41,814 POSTS
Have you tested the engine compression?
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Friday, January 13th, 2012 AT 3:35 PM
Tiny
BLACK3KBEAUTY97
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Yes engine compression is good
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Friday, January 13th, 2012 AT 5:51 PM
Tiny
KHLOW2008
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Is the firing order correct?
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Friday, January 13th, 2012 AT 6:40 PM
Tiny
BLACK3KBEAUTY97
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Yeah cause itll run good with only 3rd cylinder unplugged but of course it shakes and stuff when its unplugged, and the valves are good, it happened when I unplugged 3 and 5 at the same time by accident would that have any effect on it doing this?
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Friday, January 13th, 2012 AT 7:22 PM
Tiny
KHLOW2008
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Which engine do you have?
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Saturday, January 14th, 2012 AT 10:12 AM
Tiny
BLACK3KBEAUTY97
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3.0 sohc non turbo
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Sunday, January 15th, 2012 AT 4:03 AM
Tiny
KHLOW2008
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When firing order of one cylinder is wrong and the other isunplugged, it would run and if 2 wrong firing are working at the same time, the engine would most probably stall or run extremely rough.

Refer to the diagram to see if everything is in order.

If the ignition coil is failing, unplugging pulug wires can damage it further. You mentioned replacing almost everything related with ignition, was the ignition coil checked/replaced?

If everything fails, the best thing to do is to start with basics.

Did you replace the spark plug wires?
What were the engine compression readings for each cylinder?
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Sunday, January 15th, 2012 AT 7:54 AM
Tiny
BLACK3KBEAUTY97
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Everything is hooked up right, and about 2 months ago I got a new coil and it didnt change anything
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Sunday, January 15th, 2012 AT 4:53 PM
Tiny
KHLOW2008
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Were the injectors checked?
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Sunday, January 15th, 2012 AT 7:29 PM
Tiny
BLACK3KBEAUTY97
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Idk if it could be an injector because itll run good with that one spark plug wire halfway plugged in, if its plugged all the way in itll rev with about 1/4th throttle but wot the rpms will drop and the motor is like fighting to keep from dying, and it makes a loud roaring sound from the air filter.
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Sunday, January 15th, 2012 AT 7:45 PM
Tiny
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What difference does it make if other plug wires are unplugged instead of # 3?
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Monday, January 16th, 2012 AT 11:43 AM
Tiny
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It doesnt change the way it runs, when I leave #3 plugged in and like unplug number 5 itll still bog down and die, okay what happens when #3 is plugged the way it should ill push it to WOT and they rpms will go to about maybe 3000 and then fall back down to 0 stalling, in other words instead of racing up higher like you would think it goes backwards and heads towards 0
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Tuesday, January 17th, 2012 AT 1:41 AM
Tiny
KHLOW2008
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Have you checked for trouble codes?

Based on symptoms, either the firing order is incorrect or you have a bad PCM, unless there are touble codes for you to fall back on.
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Tuesday, January 17th, 2012 AT 1:35 PM

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