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Discussion Starter #1 (Edited)
I've about had it with this truck but stuck with it for the moment. I've had a constant Misfire on #3 for about a year and a half. I've replaced the plugs, coil, wires, distributor cap/rotor, intake plenum gasket and lifters trying to get it fixed. There isn't any abnormal pressures during a pressure test and hold the pressures fine (no leak down). It is intermittent but for about 2 weeks at a time (two weeks on and then 2 weeks off) and this misfire only occurs at idle. Higher RPM's make the misfire go away (oil pressure around 42psi).
 

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Next step is to triple check your plug wire routing.

There's a TSB on Magnums about cross fire (causes misfires) when they're not routed right.

TSB 18-48-98 for the V6; they have a link to the procedure on the V8.

RwP
 

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Discussion Starter #5
Next step is to triple check your plug wire routing.

There's a TSB on Magnums about cross fire (causes misfires) when they're not routed right.

TSB 18-48-98 for the V6; they have a link to the procedure on the V8.

RwP
I just got done checking it, wiring is right and in order. Plugs aren't too bad even with the misfire. One thing i also just noticed (if it makes a difference) is that it lightly misses @ 800rpm, gets worse around 1k rpm and then stops at 1200rpm.
 

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"Plugs aren't too bad" ... plugs are cheap enough for coppers that I'd highly consider new plugs anyway; you're talking under $10 at RockAuto or Amazon for a set of 6, and cheap enough to try for your cousin and mine, Justin Case.

After putting them in, I'd run about 100 miles, and then pull cylinder 3 and read it also; this will tell you a lot without any fancy equpiment.

RwP
 

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Have you verified that injector number 3 is ok?
Grab an automotive stethoscope and listen to all 6 injectors. You'll hear a very noticeable difference if number 3 is sticking.
Also, you can simply unplug the injectors one by one and measure the rpm drop too
 

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2 things I'm wondering. 1) Is the distributor and rotor tuned to manufacture specs? Even the slightest deviation in advancement can cause a misfire at idle. 2) It's possibly the ECM, but on a 3.9 I wouldn't think that would be the case. Otherwise, given what you've replaced I'm puzzled.
 

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2 things I'm wondering. 1) Is the distributor and rotor tuned to manufacture specs? Even the slightest deviation in advancement can cause a misfire at idle. 2) It's possibly the ECM, but on a 3.9 I wouldn't think that would be the case. Otherwise, given what you've replaced I'm puzzled.
If there's anything wrong with the distributor, it would most likely cause issues with more than cylinder #3, i.e, a multi cylinder misfire
 

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Have you replaced the distributor itself? The gears could be worn. A individual tooth could be damaged causing a misfire on an individual cylinder. Especially since its only at idle. Is there play it the rotor? (Beyond a millimeter or two.)
 

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Have you replaced the distributor itself? The gears could be worn. A individual tooth could be damaged causing a misfire on an individual cylinder. Especially since its only at idle. Is there play it the rotor? (Beyond a millimeter or two.)
Could even be play in the piece that attaches to the shaft and runs through the magnetic pickup. The part below the rotor I mean
 

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Discussion Starter #13
Have you verified that injector number 3 is ok?
Grab an automotive stethoscope and listen to all 6 injectors. You'll hear a very noticeable difference if number 3 is sticking.
Also, you can simply unplug the injectors one by one and measure the rpm drop too
injector 3 is working properly. I bought a new injector just in case and I've also flipped it from 1 to 3 to see if the misfire follows it and it still stayed on three
 

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Discussion Starter #14
Have you replaced the distributor itself? The gears could be worn. A individual tooth could be damaged causing a misfire on an individual cylinder. Especially since its only at idle. Is there play it the rotor? (Beyond a millimeter or two.)
Wouldnt I have more issues than just cylinder 3 if that was the case? If that sprocket was off it should have other misfires and more often than solely #3
 

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Have you done a compression test on all the cylinders? It's unlikely only one cylinder would have low compression, but it's possible. It would also give you an idea of the condition of your valvetrain. It's not a direct injection, as you know. Possibility #3 cylinder pinged a valve. Good luck.
 

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Discussion Starter #16
Have you done a compression test on all the cylinders? It's unlikely only one cylinder would have low compression, but it's possible. It would also give you an idea of the condition of your valvetrain. It's not a direct injection, as you know. Possibility #3 cylinder pinged a valve. Good luck.
i did and every cylinder came back at 155-160 psi except for cylinder 3, at 150.It was a minor difference but still different so i did a leak down test on it and sure enough my intake valve has a minor leak. im running cleaner through the engine now to see if it's sludge/carbon build up or a bad valve due to mileage
 

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I've about had it with this truck but stuck with it for the moment. I've had a constant Misfire on #3 for about a year and a half. I've replaced the plugs, coil, wires, distributor cap/rotor, intake plenum gasket and lifters trying to get it fixed. There isn't any abnormal pressures during a pressure test and hold the pressures fine (no leak down). It is intermittent but for about 2 weeks at a time (two weeks on and then 2 weeks off) and this misfire only occurs at idle. Higher RPM's make the misfire go away (oil pressure around 42psi).
Why would yo go mechanical!!! first things these days go should be electrical. remember 2 simple things, do you have gas, do you have gas, everything else is electrical
 

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Discussion Starter #19
Why would yo go mechanical!!! first things these days go should be electrical. remember 2 simple things, do you have gas, do you have gas, everything else is electrical
i already tested everything electrical and it was all sound. I did a leak down test and theres an issue with my intake valve causing it to mis/backfire
 

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i already tested everything electrical and it was all sound. I did a leak down test and theres an issue with my intake valve causing it to mis/backfire
You may have a collapsed lifter that won't pump up until oil pressure increases at higher RPMs. That could also cause a low compression reading on that cylinder.
 
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