2024 6.6 Gas Misfire

[transam617]

I bought my 2024 3500 just recently, and have put around 1000 miles on it, and I notice a very slight misfire at idle.  Its always been there and I just chalked it up to break-in time but it hasn't gone away.

 

Typically its only every few seconds or so, but seems random, and does not change with cold to hot coolant.

 

I've changed the oil twice during break in with no metal I can see in the filter or oil.

 

On my torque app + Elm327 setup, I can watch the O2 sensors and both banks seem fine, but I can post graphs of them if it helps.

 

I have yet to actually pull the plugs and wires, or do any testing with a cable clamp to see if I can find a bad plug/wire/coil.  I also havent check the electrical system out, the truck has dual batteries dual alternators and I do notice quite a bit of engine-speed whine like an alternator is going bad.

 

I also found this TSB 24-NA-042 (attached) that calls out O2 sensor pigtails contacting the exhaust, but I checked all the sensor wires today and mine look fine...

 

Does anyone else have an idle misfire?

MC-10251912-0001.pdf

Edited January 26, 2025 by transam617
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[CamGTP]

Most higher end scan tool can actually watch cylinder misfires. If you can't log that with the ELM327 things, then you really have no idea if it's a misfire or not.

 

Both my HP Tuners software and my Autel diag scanner can read individual misfires, that what I use to verify issues like this.

 

The low idle rpm these trucks run at can make it feel like a misfire and honestly random idle misfires can just happen. If the check engine light isn't on, then it's not doing it enough to trigger the misfire detection.

[transam617]

Thats honestly good feedback.  I am looking at getting a scanner like you suggest - any recommendations?  Something like an Autel MX900?

[CamGTP]

Yes, that is a good scanner in my opinion.

 

I have a Autel MS906MAX.

[Pryme]

The scangauge 3 has a misfire count as one of the options you can display. I had it on mine for awhile but it was always 0 so I used something else. I’d never be checking over a brand new truck with 1k miles on it like it’s a 20 year old beater that I’m looking over in a barn before buying. 
 

bring it in, you paid for the warranty when you bought your truck. 

[dal1980]

I notice this every so often with mine as well, 2024 6.6 with 10k miles.  Doesn't alarm me as my two 5.3's before this did it too.  I believe, as posted above, it's inevitable with the low idle on the trucks.  It just feels like an occasional stumble at idle.  No pattern and not really repeatable.

[bruceb58]

The engine ECU is what calculates the misfires...not the scanner. Almost any scanner should be able to display the ECU data for misfires.

[transam617]

I just wanted to come back and update, since this was not a straightforward diagnosis!

 

I ended up getting an Autel MX900, and that helped a lot.  The truck isn't latching misfires into history, but I can watch it count misfire cycles at low speed but not record them.

 

I swapped all the plugs and coils and wires around, to try to induce a predictable misfire, including indexing the plugs, with no luck.

 

I ended up changing the oil, and noticed a fuel smell, which was a good clue.  On that symptom, I disconnected the PCV system and capped the vacuum and the idle got a bit better, and the fuel trims went up.  Meaning the crankcase had fuel vapors.

 

Long story short, the dealer I bought this truck from, took delivery 8/23, and I bought it 11/24.  You can guess how long that fuel sat in the tank and lines - and most importantly injectors!  I suspect the injectors are just so dirty, the fuel trims are responding to horrible spray patterns (incomplete burning) by pulling fuel, but even then I likely had some cylinder washdown getting into the oil.

 

So I made sure with the scan tool that the HPFP wasn't leaking by doing a shutdown test.  You run the motor and look at rail pressure, then turn the engine off but keep the key on, and watch the rail pressure.  If it rises the system is sealed and is expanding from fuel soaking up heat in the engine V.  If the pressure falls that's a leaking injector or HPFP.

 

I've run a full tank of fuel through with 3 bottles of techron, and it seems to be getting better, but another thing the Autel lets me do is an injector balance test, and it's still pretty uneven.  Hopefully techron is all I need and not new injectors!

 

Pic of the truck, just got new wheels/tires.  I bought the wheels because they're 4500lb rated KMC's, and the red color was wayyy cheaper, but it's starting to grow on me.

[BCGM]

Nice looking  truck !

[lineman1234]

Misfire, yes. 2024 3500 gasser. My battery crapped out and  i did have the before cat 02 sensor or 1 of them fall on the exhaust and give a misfire code. 

     About the time i got to the dealer for my free battery, the wire burnt to the exhaust and between both the batt and it, tossed 5 codes i didnt memories what they were. But definitely a few misfires. 

      I think the miledge was about 32,000 miles or so, a couple months ago.

 

I think both were just a freak thing, and have nothing bad to say about the pickup.