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Old 05-25-2018, 05:39 PM   #1
Tomakze
 
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Default My truck has a misfire only when the engine is up to temp.

Just like the title says, my truck is misfiring once it is warmed up. (I have a 1990 4cyl 2wd) It seems to run fine when when cold. This issue started a couple months ago, but was very subtle. I took it to a mechanic to have the timing chain replaced, and asked him to look into the misfire at the same time. He said he couldn't find anything wrong, but in his defense, the misfire was very minor at that time. Now, it is not. The truck stumbles badly on takeoff, but once I get moving, it runs like a top. I have no check engine light on. The idle is perfect when cold, but once warmed up, it misfires at idle and seems to idle too low sometimes, especially if I am restarting it.

Any idea what could be wrong? I've been racking my brain for a while trying to figure out what it could be. I listened for a vacuum leak, but heard nothing obvious. I also pulled the plugs and checked the gap, and all of them look great. I have newer spark plug wires, and a newer cap and rotor on it. They were replaced about a year ago, with the plugs. I want my truck to run perfect again!
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Last edited by Tomakze; 05-25-2018 at 05:45 PM.
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Old 05-25-2018, 06:53 PM   #2
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I always recommend checking the timing with a timing light first. Should be 10 degrees btdc. Pull the codes to see if anything is failing. With it starting after it’s warmed up I’d suspect something like the oxygen sensor or coolant temperature sensor.
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Old 05-25-2018, 06:56 PM   #3
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Have a look at this thread. There's a known bad spot in the wiring harness that powers the injectors. Basically what happens is the crimp connectors go bad and the injectors stop getting full power. You can test it by grabbing the harness towards the firewall and jiggling it around to see if anything changes. If you've already tried everything else and it hasn't fixed it this probably will.

http://www.infamousnissan.com/forum/...ad.php?t=25332
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Old 05-26-2018, 05:24 PM   #4
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Quote:
Originally Posted by alabama_lowlife View Post
I always recommend checking the timing with a timing light first. Should be 10 degrees btdc. Pull the codes to see if anything is failing. With it starting after its warmed up Id suspect something like the oxygen sensor or coolant temperature sensor.
I was thinking about the O2 sensor as well... Hadn't considered the coolant temperature sensor though. Would that cause it to treat the engine like it is cold all the time, and make it run too rich? That would make sense. I know the timing is good, because the issue didn't change when the timing belt was replaced.

Quote:
Originally Posted by SBJ View Post
Have a look at this thread. There's a known bad spot in the wiring harness that powers the injectors. Basically what happens is the crimp connectors go bad and the injectors stop getting full power. You can test it by grabbing the harness towards the firewall and jiggling it around to see if anything changes. If you've already tried everything else and it hasn't fixed it this probably will.

http://www.infamousnissan.com/forum/...ad.php?t=25332
That is very interesting... I may rewire that either way, just in case. If that is a common problem, I might as well avoid having issues down the road, and that fix is free! Thank you!
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Old 05-27-2018, 04:56 PM   #5
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could be a bad plug wire that is arching against metal also, if wires are old replace with OEM or NGK
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