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Discussion Starter #1
Started off had a misfire on cylinders 2 and 8. Replaced all plugs and wires. Brand new distributor and replaced every sensor possible. Dine compression check and needless it was bad on cylinders 2 and 8. So I pulled engine and rebuilt completely. EVERYTHING is brand new. Put back in the truck and I have checked 400 times over and everything is plugged back in correctly. No vacuum leaks and timing is perfect. I drive it down the road around 10 miles and engine light comes on saying misfire on cylinders 2 and 7. I 've checked everything possible. Any suggestions before I roll it down the hill and bury it???
 

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fuel injector - did you replace the plenum gasket - are the spark plug wires put back in the correct place - number 5 and 7 can misfire if not routed in the correct way
 

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Discussion Starter #6
I swapped injector wires on 2 and 4. It cleared the misfire on #2. I swapped 5 and 7 and got a misfire code on 5 and 7
 

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On the 3.9L V6 and 5.2L V8, rerouting the ignition coil wire and spark plug wires can help solve a misfire and/or surge problem that occurs at approximately 45 mph. A service bulletin was published that outlines the specifics of the repair. It states the rerouting procedure should be performed before other repairs are done for misfires, surging or spark knock.
 

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This is almost a textbook case of how not to address a repair issue, no real diagnosis, just shotgun everything.

"I replaced every sensor"...why? What evidence did you have that any of them were faulty? A faulty sensor would throw codes, and would not create consistent misfires on just two cylinders. Why would you replace the plugs, wires, and distributor before doing a compression check? An ignition-related miss is different than a miss caused by poor compression or valve problems. That would have been easy to determine.

So you did a compression check, and had bad cylinders. Did you do a teardown to see why they were bad? Maybe you didn't need a total rebuild.

"I rebuilt the engine completely". By yourself? In your garage? Or do you mean you had it rebuilt professionally? There's a big difference here.

You say you put it back together and checked it "400 times", but you've got an immediate CEL for misfires...so obviously you didn't "check" something.

"Timing is perfect". As well it should be, it's set by the PCM, and is not even adjustable.

"Everything is brand new". Maybe it is. But the problem with that is that now you don't know what, if anything, was faulty to start with. You also don't know if among those many "new" parts there's something defective causing new problems.

When you have an obvious problem like a misfire, you need to approach it systematically, starting with the simplest and most obvious things. Did you put the plug wires on correctly? Did you crack a plug while installing them? (I've seen a lot of guys do this, even some shops). Is there a defective plug in the bunch you've bought? (I've had this happen, it's rare, but possible). Is there a bad plug wire, with a broken conductor you can't see? Do you have an intermittent injector, or a bad injector harness with a broken wire, or a bent pin in an injector? There's a million little things that could cause these problems that need to be looked at in a logical step-by-step fashion. What you've done so far is buy a lot of parts and spend a lot of money, and now you're frustrated with the vehicle and the whole process.
 

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Discussion Starter #11
First off I came here looking for suggestions not smart ass remarks. Second off I did everything in a step by step process started with the simple stuff first. I am no professional but I'm not a rookie by far. This is not the first time I've put my hand on an engine. So Thanks for the info but an even bigger Thanks for no help
 

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I have had the center button fall out of a new distributor cap. ran horrible - took a bit to find it because it was a new part.
 

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First off I came here looking for suggestions not smart ass remarks. Second off I did everything in a step by step process started with the simple stuff first. I am no professional but I'm not a rookie by far. This is not the first time I've put my hand on an engine. So Thanks for the info but an even bigger Thanks for no help
If you want help, you have to give us something to go on. When you make blanket statements like "I replaced everything" that actually tells us nothing, because we have no idea what you think "everything" is, or what process you followed, or if you even did it right. I assume nothing. Similarly, when you say the engine is misfiring on 2 and 7 after you "fixed" it, that also tells us nothing. Is it a hard misfire? Partial? Random? Intermittent? Does it misfire at idle, or under load, or both? Did you check for spark? Did you check for injector pulses? Did you check compression? Did you check valve lift? You're leaving out a vast amount of information, which is why you're not getting much of any help. Sorry if you think I'm being a "smartass", I'm just telling it like it is.
 

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I swapped injector wires on 2 and 4. It cleared the misfire on #2. I swapped 5 and 7 and got a misfire code on 5 and 7
Magnum engines have sequential fuel injection. You can't "swap wires". The cylinder will not get fuel at the correct time. What he meant by swap was physically move the injectors from one position to another...not swap wires.
 
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