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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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