I've posted about this before and no one has been able to shed any light on this mystery. My Dodge 1500 5.2L has 114,000 miles. I bought it in May 2005 and drove it for barely a month when it started encountering problems. I had the tranny, crankcase, and radiator flushed. I installed all new filters and a new serpentine belt. The truck started misfiring around late June. I installed new plugs, a cap, rotor, and plug wires. I went so far as to route the spark plug wires in accordance with the Dodge TSB and *STILL* there's a msfire. I took the truck to Autozone, and an assistant there plugged the diagnostic to the computer on my truck and the code returned a misfire on cylinder #6. I pulled plug #6 and it appears slightly oil fouled, but not soaked. I ran a compression test last night on cylinders #8, #6, and #4, all of which posted a healthy 127+. My dad suggested that the gap between the rotor and the other part inside the distributor (I can't remember it's correct name) might not be at .008 like it should. I am wondering if a worn valve guide is possible for the misfire, since #6 actually posted the best compression. About another week and I plan on pulling my truck into the garage and tear into the engine. I also suspect the intake pan gasket is torn and I feel the throttle body should be cleaned.

Can anyone offer any other suggestions?

 

There was one thread like this but I dont remember if its the same one. Have you checked your injectors? Somebody had a really good idea of pulling the injector on the bad cylinder and swapping it with another one. If the misfired follows the injector, bingo.

 

check for burnt valves.

 

Plug slightly oil fouled? I'd think plenum gasket or valve seal. Gasket makes more sense, cause the oil fouling should burn itsself off if it was caused by leakdown from a bad seal. I would try the injector swap also.

 

I was studying the Haynes manual I have and read up on misfires. There is a procedure there where the engine is running and an injector is unplugged. The idle should change in a notcieable manner; otherwise, it's a faulty injector. I am going to try that, but something tells me it's either the plenum gasket or a burnt valve.

Thank you for taking the time to respond.

 

Mr Racin is probably right on with the plenum being bad... oil fouling on the plug is another sign that the plenum is leaking.

If when you pull the TB and use a mirror to look around inside the intake, you do not find oil pooling down there, then it is possible you have a cracked head. that is the other cause for misfires that cannot be traced to ignition or a worn cylinder. The only way to verify a cracked head is to pull it off.

 

Well, fired up the truck tonight to take the trash out for collection tomorrow (I have to haul my dumpster 1/4 mile). When I returned to the house, I decided to test the theory that an injector is misfiring. I unplugged #6, and no change in the idle. I pulled #8, and WHOOPS, that was not good. So I reconnected #8 and pulled #4, same change in the idle. I reconected #4 and disconnected #6, and again, no change in the idle. I drove back down to the end of my road and down the main drag, stopped, reconnected the injector, and headed home. Didn't seem like there was a problem at all. Stopped part of the way home and disconnected #6 again, and no change all the way home. Once I got home I started experimenting with the remaining injectors, and of all things #5 didn't appear to phase the idle either. Very interesting. I have a friend coming over this weekend who works as an aviation electrician. I think we might pull the wires from the injectors and perform some continuity tests on the harness as well as the injectors. I may pull a couple as well.

I am not fully convinced that the pan gasket isn't a problem; however, I am suspect of an injector problem.

 

watch out for them AT's...they can be a bit shady!!! just kidding... thats a good idea..make sure your wiring is good first .. ill bet you got a few messed up injectors.. stupid qeustion but have you ran a bottle or 10 of cleaner through it ? whenever im runing ruff i run a few bottles and 93 octane and cleans it up nice and good

 

I played BM for a while and was a DP on board CVN-70. He can't pull anything on me

Good idea about the cleaner, but I believe the best medicine would be to pull all of the injectors and clean/test each one. It can't hurt. Oh yeah, my muffler and/or cat rattles like a sonuvabitch. I am going to make a call to the dealer about replacing that while I'm at it.

 

do what someone else suggested by moving the 2 injectors to other locations. I suggest swapping them with 3 & 4.

you mentioned putting new plugs cap & rotor in, have you pulled the plugs since then? yank 5 & 6 and see if they are gas fouled, if not, put them back in and put a timing light on the wires and verify spark. then verify (using a screwdriver or mechanics stethescope) that the injector is actuating. you should be able to hear it pretty easy with the scope.

the one thing that stand out in this thread is the fact that you had the tranny worked on, then a miss-fire after that. it is possible that the flex plate got hammered enough on the tranny install to cause the CPS to loose the signal on those 2 cylinders. they are back to back on the firing order which would mean that the section on the flex plate would cover both cylinders are right next to each other.

I read a long time ago a thread where a guy had a problem, cant remember the details unfortunately, and the problem turned out to be the flex plate. it got hammared in the tranny install and caused some problem with the motor.

HTH and let us know what you find.