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Engine problems

Drache

Drache

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Aug 14, 2015
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British Columbia
Ok I'm having a problem with a random miss in the number 6 cylinder on my 3.9L

I've changed the injector (even swapped injectors on other cylinders), changed the spark plug (even swapped spark plugs on other cylinders), tested the spark plug wires, and changed the distributor cap.

Now the weird thing is, the one mechanic I took it to couldn't figure out the problem. He said the random misfire only happens at idle. Not when actually driving the truck.

What else could be causing the problem?
 
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Sounds like you've changed out the obvious stuff....I'm wondering if there is an issue with the valve train, or a carbon-ed-up valve.
I had a serious miss on No.1 in my GTX years ago...it was a spark plug. Damn thing wouldn't let me go over about 40mph in top gear.
 
mmm....that's not leaving a lot of things to look at.
 
Random misfire can be caused by about anything that moves and can knock. Have solved it by replacing tierod ends. Time to start looking at the not so obvious.
 
Does the computer throw out any code? That's about the only other thing I can think of. Even if it doesn't produce any codes, it could be causing it. How about looking at all the connectors to it? I recently had to do some work on the bulkhead connector on my 95 due to corrosion. I also made a water deflector to keep the water from hitting it whenever the hood was opened plus the rubber deflector wasn't doing a good job either.
 
How about the wiring to and or injector connector? I've seen these "noids" you can buy to hook to them for testing. Don't know about those ones..........

Wiggle the connector while running, unhook it and see what difference........

Do these have the bottom intake cover like the V8s?

What does the plug look like? I still "lean" (pun intended) towards vacuum leak. Remember, they can leak from the valley, as well.
 
check the throttle plates for carbon buildup. i have been having trouble withe my engine dieing at idle. in my search for a fix i found out that the plates should be closed at idle. and if you mod the throttle body to crack open the plates the computer will try to adjust for that. also some guys do a mod to the TPS by drilling the holes a little and rotating the TPS housing. there are some good posts on some other sites about dieing at idle that have a lot more info. also when starting the engine dont open the throttle plates. because the computer uses that as a " 0 " set point for running the engine.
 
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