[dakattack]

I'll throw my 2¢ in here as I just had a similar situation the other day (on a 3.5L 300, but same issue.)

It had a 1, 3, 5 misfire code and, watching them, they'd miss and then go away and them miss again. Others had dealt with this by replacing coils, plugs and 3 PCMs with only a temporary change. When I got it, I swapped the injectors with no change, ran a leak down and a hot compression test and everything checked out good. I finally decided to pull the head and found the problem, all 6 exhaust valves were burnt!

The valves are designed to rotate to keep the face clean and it was fine until the burn mark on the valve and the burn mark on the seat lined up and then it'd misfire until the valve rotated past the bad spot. You could have a similar issue.

As others have said. A chain would effect all the cylinders, a camshaft would more than likely cause a constant, not intermittent, misfire, and you,ve replaced pretty much everything else. If it were me, I'd pull the head and check it out??

If it's in good shape otherwise, I say fix it and keep it.

 

[bill ball]

ARGH! You know, I like working on cars, to an extent, and I'm in the middle of rebuilding a tranny on one of my other cars and it's been a chore. Can the 5.2 heads be pulled without pulling the motor? It looks like they can from the FSM I have, but we have a saying on another auto message board, "Real men pull the motor" and I'd like to avoid that! I've suspected something mechanical because of the coincidence of it appearing immediately after the over-rev even though, like you found, compression and leak down checked out OK.

 

[dakattack]

Absolutely! Very easy to do and you don't even have to pull the distributor out. If you have a lift, you could have the head, or heads, off the motor in about an hour.

 

[bill ball]

An hour, you're fast! So the lift eases getting at the exhaust manifolds I'd guess? Actually the manifold bolts appear to be very accessible from above and everything else appears to be up top so why the lift?

Right now the lift is occupied by the car with the tranny out so I'll probably go ahead with this in a few weeks after I get the other car running.

 

[dakattack]

The manifolds are a lot easier to remove with the heads off, especially if you have to replace the cat anyways. Installation is also easier.

 

[MWeed]

It's easiest to go in from the sides for the exhaust manifolds, that's why the lift. Once they're off, the rest is done from the top. With the heads gone, now would be the time to replace the stocker intake with an M-1 and remove any repeats of "Belly Pan Fever." A good set of R/T heads and you're off to the races? er back on the road.

 

[bill ball]

M-1?

 

[MWeed]

The M-1 is a conventional styled performance intake manifold that looks like a standard aluminum 4 barrel carb manifold from the hot rod world. It eliminates the belly pan gasket any resultant problems with same. Plus it just looks sexy.

 

[bill ball]

Ah, I probably couldn't sneak that by any legitimate smog shops here in NorCal.

 

[MWeed]

I have one on mine and it passes with no problems here in the LA area and others have had them pass up North also. When I first did mine, the inspector hiccuped over the K&N FIPK I had on there, but I showed him where my sticker was for the exemption and he passed it with no problems. The M-1 comes as a 2 barrel or as a four barrel manifold, be sure to get the 2 barrel for our throttle body with no EGR.

 

[bill ball]

Today the CEL came on again as usual, but after a few more trips, it didn't come on a restart. The FSM emissions chapter notes that misfire codes will be erased if there are no misfires in 1,000 revolutions on three successive trips. Oddly, the engine idled more roughly after the CEL went out?? It appears it has to accumulate some number of misfires over some period of time before it'll throw the code, but the FSM doesn't define that.

 

[bill ball]

Today the CEL came on again as usual, but after a few more trips, it didn't come on a restart. The FSM emissions chapter notes that misfire codes will be erased if there are no misfires in 1,000 revolutions on three successive trips. Oddly, the engine idled more roughly after the CEL went out?? It appears it has to accumulate some number of misfires over some period of time before it'll throw the code, but the FSM doesn't define that.

UPDATE
Weird but good. The CEL went out, it ran a bit rough for a while even with the light out, but for the last 2 days it's run fine and the light has stayed off. I have no idea what happened, I can only hope the problem is resolved. I was planning on pulling the heads, but I'll hold off unless the problem returns.

I'm going to take it down tomorrow for another try at smog testing.

?this vehicle is possessed!

 

[dizzyD]

Quite possible the PCM reset. I know with a battery disconnect and a "hold the key at start for 10 sec while the battery is disconnected", the PCM resets to initial specs. It ran rough for the first 5 minutes of driving and even wanted to stall once coming to a fast stop.

 

[Durangutan]

The intermittent and baffling nature of the issue just seems to point to the PCM. I realize this is unrelated, but have you pulled the plugs off the PCM to see if you've got any power steering fluid creep?

Another thing that causes odd behaviors on the D is battery problems. I had what I swore was a perfectly good battery, yet I had unexplained rough idle, low RPM, occasional dying, and random CEL flashes that all turned out to be due to a bad battery.

Just a few random 2¢.

 

[bill ball]

Appreciate the PCM reset suggestions and checking the connectors. Will do.

UPDATE
The D continues running great and has thrown no more codes so, I ran one more can of Seafoam through the intake, went for a long highway drive, and took it to smog test again. Remember, it has all new ignition parts except the coil, new fuel injectors, new O2 sensors, reasonable compression and perfect leakdown numbers. After all this, it flunked worse than ever! The NOX was over 1800 and it's now labeled a gross polluter. HC and CO are moderately high but passing. The tech ran a manual test after the failure and, at idle, it generated almost no NOX and very little at 2500 RPM, but during the smog test, which is under dyno load, it pukes NOX.

I can't see any other option at this point except a new catalytic converter, which is about $400 for a direct bolt-in replacement that's CARB approved. But, it should be throwing a "cat inefficiency" code I'd think, although I'm not sure how the rear O2 sensor does that if all it measure is O2 content. Anyway, I'm not to thrilled about spending another $400 to potentially accomplish nothing? I spent close to that already with zero results!

Sure, I could replace the control module, about $200 rebuilt and correctly coded, but this would seem to me to be a very odd form of PCM failure.

I heard the 318 is infamous for wearing out cams. Could poor emissions with high NOX be related to worn cams? If so, it's going to be a trade-in. That's where I think I'm headed regardless.

2nd UPDATE
I found a CARB approved Magnaflow cat (model 45006) for $150. I'll cut out the old one and do a slip-on (I have pipe expanders if needed) with clamps and see if that takes care of the problem. I'll let you know in a few days.

 

[tomk]

NOx usually comes from something that causes high combustion temps, though the cat apparently does reprocess NOx when things are right (so a cat replacement may fix the problem.)

High combustion temps can come from lean mixture or pre-ignition (spark knock.) Were you running decent gas for the test?

?tom

 

[dizzyD]

As Tom mentioned, the gas station could have pumped you some bad gas or just the quality of the gas at a particular chain station my be at issue. My old Dakota failed smog 3 separate years! The first year it was the cat failing, at the time I ran ARCO gas not a top tier rated brand. 2 smog checks later it failed again, barely, so I threw a bottle of Lucas in it and it passed. The last year I had it, it failed the HC's IIRC. Another new cat and it passed, barely. It had 166K on the motor and I ran it hard.

I started using 76 and Chevron gas the past 3-4 years and, although my DD 92 Lexus recently hiccuped on smog, after I threw a bottle of the Lucas in it, it passed the next time. It'll probably need new cats next time around.

 

[bill ball]

I had my local muffler shop cut out the old cat and weld in the replacement, charged me $85, and when the old one hit the floor, I knew we'd found the problem. It was a totally plugged, melted mess inside, the muffler guy also commented it was way too hot. Anyway, the back-pressure and exhaust gas reversion was causing the high combustion temps and high NOx and the over-rev probably just knocked some carbon loose that further plugged the cat causing the idle roughness and occasional misfire code.

Here's my 15MPH smog test prior to the new cat: HC 82, CO 0.52, NOx 1895

And with the new cat: HC 10, CO 0.01, NOx 0

So, if any of you have grossly high NOx without good evidence the fuel is too lean and you're in CA, grab one of the Magnaflow 45006 and have it welded in by your local muffler shop.

For the past year, I'd thought the top-end was more gutless than it should be and it developed an odd exhaust drone when I jumped on it at higher RPM, I was concerned perhaps the cams were going. Off the line and cruising around (low RPM and lower exhaust flow) it seemed about the same as ever. With the new cat, it's now much better at the top end, say when I go to pass on the freeway, which makes sense.

So, my car problems are receding now that I have the tranny fixed in my other car and the D is doing well again.

 

[Siggi Gunda]

Good to hear you got it fixed and we now have more experience. Thanks for keeping us updated, this one goes in the bank. :thumbsup:

 

[MWeed]

Did the miss just go away with the new cat? The miss, along with a lot of your previous problems, could have destroyed the old cat. An engine that runs rich can burn a cat up and a miss would cause raw fuel to be dumped directly into the cat and cause this to happen quickly. So the question is, is everything now running 100% or is there still a rough idle or running problems you're not aware of now because they're hidden by the new free flowing cat? If all is fine, then great and I'm glad for you.