Dodge Durango Forum banner
Cancel
Create thread New Garage Forums

Rough idle after over-rev ? Fixed - (New cat converter)

Jump to Latest
19K views 66 replies 13 participants last post by  bill ball  
B
#1 ·
UPDATE 12/31: After going through days of rough idle and "misfire cylinder 6" engine codes, despite all new igntion parts and fuel injectors, it all cleared up. The D is running fine, but it flunked smog worse than ever.
UPDATE 01/07: IT WAS THE CAT CONVERTER. Runs better, perfect smog result with new CARB-approved cat. So, the over-rev didn't hurt anything but probably loosened up some carbon that finished plugging the converter. The old converter was a complete mess.
=============================================================================
Our 5.2L 99 D has 124K miles and was running real well, but recently it failed smog for the first time with very high NOX reading. I replaced the plug wires and plugs (which were REAL bad), but it still failed with exactly the same numbers. So, I ran a couple of cans of Seafoam through it, one into the intake and one in the tank.

It seemed to be running perfectly OK, but while I was fiddling with it yesterday preparing to take it back in for another smog test, I inadvertently over-rev'd the motor. Not too bad, just into red-line area very briefly, but when it returned to idle it had a noticeably rough idle. Seems to be missing one or two cylinders.

OBD shows no codes and I can't find any vacuum lines that might have come off. Pulling spark plug wires seems to show no change on cylinder 1 and 6. It's rather hard to tell, but most of the other cylinders show an increase in roughness if the wires are pulled. Same with the injector wires. Spark is good to all plugs and OBD doesn't show any codes except when I pull one of the wires. All the injectors are firing based on a vibration sensor I use.

Anyway, it looks like I have one or two dead cylinders. Like I said, this appeared IMMEDIATELY after I briefly over-rev'd the motor. It doesn't appear to be an ignition related miss since there are no codes.

I'm stumped. Could I have bent some pushrods?

Bill in Alamo, CA
99 D SLT

UPDATE
Just went and rechecked and it seems it's just cylinder 6; the exhaust manifold measures cooler there as well. My #1 suspect would be a plugged #6 injector, which was just coincidental with the over-rev.
 
B
#52 ·
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!
 
#53 ·
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.
 
Save
Reply Quote Like Like
#54 ·
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¢.
 
B
#55 ·
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.
 
#56 ·
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
 
#57 ·
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.
 
Save
Reply Quote Like Like
B
#58 ·
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.
 
M
#60 ·
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.
 
Save
Reply Quote Like Like
B
#61 ·
The idle roughness and cylinder 6 miss was erratic and disappeared several days before I changed the cat. I think the cat had been in bad shape for years because, when I looked back at the old smog test results, the NOx was 950 in 2009 (not quite high enough to fail at 980, but awfully close and a sign that something was wrong.) The D gets "truck" smog limits, which are about twice that of cars in this case, and my top end performance was already down at that point. So I think the cat had been getting progressively worse over time and I just didn't know the root cause. It may have just been an inherent cat failure and the intake treatment with Seafoam made things somewhat worse by adding carbon to the plugged up melted mess.

It may be that other early D owners are experiencing worsening smog results but not outright failure like I did until this year. I also believe many states don't test for NOx and, if CA didn't, I'd have passed despite a totally messed up cat. Kinda glad the failed smog test caused me to fix this!
 
M
#62 ·
You're right about keeping up on these things. I have a new cat in my D at ~145k for the simple reason that it kept blowing gaskets between my Y-pipe and the cat. No other symptoms like high readings or such, just every month and a half the gasket would blow. No problems now. With everything I have on this puppy from K&N FIPK, Fastman TB, M1, 1.7 roller rockers, headers and all the stuff to better my off-road running, it runs real clean and hard at 160k. I intend to keep it till the fenders fall off? and then replace them with fiberglass ones.
 
Save
Reply Quote Like Like
#63 ·
Your fenders won't fall off in SoCal? maybe if you lived in the local mountains. Only way mine would fall off is if me or my wife sideswiped a semi or something similar (knock on wood.) I did have an near hit this morning coming home from work on the 710 to 91 interchange, A Mustang (newer one) must have had the rear end lock up as it was straddling two lanes. Four cars behind it had to jockey to avoid it and I used the shoulder the bridge and must have cleared the railing and Mustang with less than 6" on either side. You couldn't see it until the last 100 ft what with the smoke from all the tires and the foggy conditions, which has started back up again in the valley.
 
Save
Reply Quote Like Like
M
#64 ·
I know. At least that means I'll have the D for a long time. It's now starting it's 13th year with me, kinda like a friend.

I know the fog you're talking about and at least it's not the nasty stuff from up in the central valley that causes those 15 car chain reaction wrecks. Drive safe.
 
Save
Reply Quote Like Like
B
#65 ·
The D has been a good vehicle for me too. Just a family hauler, but it was real handy going on ski trips in 4WD and not needing chains. Only issues I've had were a leaking tranny seal and 2 water pumps that leaked. Oh, I did have pinging initially, but re-routing the plug wires per a TSB and installing a 160° T-stat resolved that (I've run 87 octane since with no issues.) I fixed those myself, so it's never had to go to the dealer for any repairs. No problem with the front ball joints or the intake gasket. Gas mileage with the old 5.2 is pretty terrible, although I expect it to improve some with the fixed cat. Still, the family is downsizing, so the D is about to go up for sale for something smaller and much more fuel efficient.
 
#66 ·
bill ball said:
Still, the family is downsizing, so the D is about to go up for sale for something smaller and much more fuel efficient.
Click to expand...
Hmmm? like a '12 JGC? :cheesy:
 
Dodge Durango Forum
posts
509K
members
60K
Since
2004
Welcome to the best Dodge Durango Forum around, where you can find a great Dodge Durango Wiki and discuss the reliability of the different trim levels including the GT and SRT!
Full Forum Listing
Explore Our Forums
Durango Discussions 2014+ Durango Discussions 1998-03 Durango Discussions Dodge Durango 2018+ SRT and Hellcat Durango Purchasing