Hello all, I am hoping to get some advice/guidance on what is becoming quite a major PITA on my 1999 5.9 Magnum 1500. It has only 90k on it and the engine is running really rough. I have a CEL (which occasionally blinks) code for a cylinder 2 misfire, and when I try to get on the gas I get a good amount of studdering and a lack of power. Also when the engine revs fairly high I get a rapping/clacking sort of sound which is predominantly heard when I let off of the throttle.

I have replaced: Cap, Rotor, Plugs, Wires, Coil, Cat, Upstream o2 sensor (Bosch), and replaced the plenum with the Hughes kit.

I recently performed a dry compression test:
Cylinder 1- 140psi
Cylinder 2- 160psi (had the most carbon buildup on plug)
Cylinder 3- 160psi
Cylinder 4- 150psi
Cylinder 5- 150psi
Cylinder 6- 160psi
Cylinder 7- 160psi
Cylinder 8- 135psi (had fair amount of carbon on plug)

Can someone please shed some light on whatever issue I may be having!? I'm really at a loss here and I'm hoping its something on the simple side like valve seals and springs.. but honestly I do not have the expertise. Any help is very appreciated!

 

Our trucks don't like bosch O2 sensors. Unplug the front O2 and see what happens. Was it running rough before you changed all that stuff?
Did you route wires correctly per TSB instructions?

 

Replace the PCV valve, and run some combustion chamber cleaner (e.g. Sea Foam) through the intake. You might even want to do the combustion chamber cleaner twice, a hundred miles or so apart.

That's not an absolutely certain fix, but it's the failure most closely associated with the symptoms you've described.

That carbon on the #8 plug may well be indicative that your catalytic converter is oil fouling, and that can lead to much more expensive problems. Oh, and that Bosch oxygen sensor is probably causing its own share of rough running, too. You should swap it for Denso or NTK -- the best bet is to score a new part from a dealership.

 

Was the compression test done before or after you changed the plugs cap-rotor and wires? If after and you have carbon build up on some of the plugs i would double check the wire roughing and make sure you have good connections on the plugs and cap. Don't waste your money on Bosch o2's go with NTK. You may have a plugged cat. Disconnect it from the manifolds and see if that makes any difference.

 

Yes it was running rough before, it all started with the typical plenum gasket symptoms: massive oil consumption, sucking noise from the air filter (it even stalled out on me a few times) that's when I got a CEL for the o2 sensor and I replaced that along with the typical tune up parts. It ran pretty good for a while and now I pretty much have a constant misfire unless I'm running at highway speed.

 

I forgot to mention I already replaced the PVC valve. And that's not a bad idea with the seafoam treatment, although I have been a bit hesitant to try it since the last time I did it there was a crap load of carbon buildup on all my plugs afterwards.. which I then replaced. As for the cat, its only a week old.. brand new. The carbon buildup on the plugs was most likely there before I had the new cat installed. I wish I knew how vital the o2 brand was before I bought a bosch, I will pick up a denso as soon as I can. As for my compression, do my numbers seem good?

 

I just did the compression test yesterday actually. I did not look at the TSB for the wire running, but I will certainly do so now. When I did run them I made sure to keep them nice and neat, following the stock white routes.

 

If any of the plugs near the intake manifold port it's connected to are still showing carbon, you might try swapping them with come good, clean plugs from other cylinders, or just replacing them with new. If they show carbon again, while those further from the PCV valve don't, you probably got a bad PCV valve. It happens from time to time that these mass produced, low dollar parts are out of spec when they leave the factory.

If you've got (or had) poor oil control that's pretty normal. I've not known Sea Foam or the Chrysler Combustion Chamber Cleaner to cause serious problems, though, because the carbon is usually softened before it breaks free. The old school cleaning method (which I won't even describe for fear that some idiot will use it) could cause all kinds of problems with solid chunks of carbon smashing spark plugs and blocking valves open, but in my limited experience neither of those two products has caused such problems.

Mostly, yeah, but I'm a bit concerned that it's #8 that's showing the lowest number. I'd want to check (all eight) again after the combustion chamber cleaning.

 

Maybe to a cylinder leak-down test. That would at least let you know what the problem was.

 

Well I guess it wouldn't be the first time I have gotten a new faulty part before.. yea I was a bit concerned about #8 being low as well, especially compared to most of the other cylinders, but is it "in range?" I will definitely give the seafoam a shot! Do you have any idea what might be causing the engine noise I have been experiencing?