2001 Dodge Ram 1500, 5.2L 318 V8 Engine. 114,500 miles.

I haven't been as active recently, seems like most of my free time goes into fixing up my pickup, work and family.

I am currently diagnosing a problem that may have been on going for quite awhile now but has started to show up more aggressively in the past week.

Here is what is going down, I have a OBDII Code reading that was stored in the computer for all of the following:

PO0300 - Random Cylinder Misfire
PO0303 - Cylinder 3 Misfire
PO0306 - Cylinder 6 Misfire

The truck is running really rough even when I clear the codes. I hear a nice pronounced "knock/chatter" coming out of the lower part of the engine bay (drivers side) that is only apparent at low idle. Oil pressure seems to be closer to the 40 (top end of the guage) than it normally was.

I had done a new oil change just last month, It always takes 5.5 qts.. this time though I didn't replace the oil filter because 2 weeks prior I had already done an oil change. I put a new K&N Air filter in prior to this problem as well.

Previous work I have done before this was extremely apparent:
I had a radiator that failed the pressure test, and a bad water pump that was leaking out the weep hole. I was told by a local dealer that my timing cover case had a leak so I had also replaced that since I was going to have it all the way apart. I marked the Harmonic Balancer Pulley (HBC) with the markings on the Timing Case Cover (TCC) for TDC. When I put on the TCC I had made sure that I let the gasket and gasket sealer cure for 24 hours, no problems with it leaking oil after that. (I had to drain the oil to install my timing case cover hence the oh so recent oil change) Installed both the water pump and radiator successfully without any leaks.. Now we have the misfire dillema.

Now I am kind of in between a rock and a hard place because I don't like to take stuff to the dealership unless its completely over my head.

Important stuff for the readers to know:
*Spark Plugs, Cap, Wires, and Rotor new as of 07/2010.
*O2 Sensors replaced 05/2010
*Dealership fixed a ignition system problem that caused a Cyl. 5 misfire 07/2010 as well.

So what I need to know, with plugs and wires (etc) done very recently, what is it that I could be missing?

Catalytic is still in good running order I'd imagine, so I think it could be a number of other things.. I don't think it's a fuel injector because it seems to be both Cylinder 6 and 3 and a Random one..

As for the lack of power, you can tell that some of the cylinders aren't firing all of the time because it's definitely a hog and in one particular case it died while idling after tapping the throttle.

Please if you have any Input I would much appreciate it, and if you help me solve my problem, My girlfriend with bake you cookies!!

Thank you in advance, and hope that this isn't some freak deal that I can't diagnose!! In the meantime, Im going to go into the garage and cleanup my tools!

 

Your lower intake gasket is blown(plenum gasket,do a search here) and the Cat is junk.

 

Could it be timing might be off?? Is there an easy way to evaluate this first?

 

NO! The timing is not adjustable.

 

Okay that's good news though I guess. Would you recommend taking it to a dealer to have them install a new one? Is that 99% probability that it's those two items? I never got a cat deficiency code yet. Dang it looks expensive.

 

yea i agree with zman17

 

Okay. I've looked at the other pages on plenum gasket replacements and it might be difficult enough that I should take it into the dealer. Thanks for your help.

 

Do the vacuum test on the plenum before changing that. Just type in "plenum, tsb" in google, then look at the test and do it. Did it just start doing it right after you did the work (immediately after)? If so, I'd say its not the plenum. Dang, zman loves those plenums. Lol.

 

Pretty much right after, but it came up all of the sudden with almost half the power output that I normally have. No leaks of anything, starts well, so not too sure what else to check.

 

Should I go back through and make sure that all the spark plugs are gapped correctly? I did use a di-electric grease, on the arm which I have never used before. I dont remember now if I set them to proper gapping.. and I did make sure all of the plug wires "clicked" into place on both the engine block and dist. cap.