6.2 High RPM Misfire

[sealandsky]

Hi there - I've recently had a high rpm engine misfire issue crop up. It happens as the engine winds through around 5,500 prm's and gets more pronounced with increasing rpm's. To my senses it's an ignition induced misfire but I"m not 100% convinced or as to why it's happening.
Background information: 2019 Yukon Denali - Callaway 6.2 Supercharged 129K miles. I did just recently (around the same time I started noticing the misfire) modified the Callaway CAI system to use an S&B airbox with extra large cone filter for better filtering and airflow. There are no codes coming up and no check engine light. When I installed the new CAI I did use MAF cleaner on the airflow sensor and let it dry before reinstalling. And the battery negative was disconnected during the work. At all other rpm's it runs great. The spark plugs were replaced about 15K miles ago.
If I was going to shotgun the issue I'd think I have a weak coil but I'm hoping the brain trust here can provide their input. Thank you.

 

[Fless]

Put a scanner on it that can show individual cylinder misfires and take a high rpm drive. Once the cylinder is identified you'll have some direction.

No cam or crank sensors changed lately? Might try a quick CASE relearn to ensure they're in sync, just to rule it out.

 

[sealandsky]

Put a scanner on it that can show individual cylinder misfires and take a high rpm drive. Once the cylinder is identified you'll have some direction.

No cam or crank sensors changed lately? Might try a quick CASE relearn to ensure they're in sync, just to rule it out.

No sensor work on this ever. But I like the direction of your thinkung!

 

[Marky Dissod]

Background info: 19 Yukon Denali, Callaway 6.2L Supercharged, 129K miles ... just recently (around the same time I started noticing the misfire) modified the Callaway CAI,
system to use an S&B airbox with extra large cone filter for better filtering and airflow.

If the misfires began AFTER you installed the S&B airbox and cone filter,
then you get the tune readjusted for the airflow profile you changed, sooner rather than later. Or, put back the previous airbox & filter, see if misfires go away.

If the misfires began BEFORE you installed the S&B airbox and cone filter, then the S&B airbox & filter either fixed nothing or made something worse.
Ultimately, either way, I'd consult Callaway.

Over-distilling down to 'high-RpM misfire' makes me think:
*check plugs, plug wires, coils, and EVERY electrical possibility branching out from there - one or more electrical grounding paths might not quite be keeping up
note that a common electrical upgrade / precaution is to add more grounding paths, like a PPV / SSV does.
*run a double strength dose of fuel system cleaner like Chevron w/ Techron or BG44K (anything with Poly Ether Amines) through ONE tank of gas ... TWICE.
If the misfire improves it was your injector spray pattern.

Would you happen to know your injectors' flow rate?

 

[West 1]

You need more information. With a quality scan tool you can watch misfires, timing, fuel pressure, long and short term fuel trims and your O2 sensor readings to try and zero in on your problem.

 

[houstontaylor]

I once got a replacement "remanufactured" ECM that caused missing at over 3,000 RPM. When I put the old one back in to check it, it didn't have that problem.

 

[hagar]

Increasing the air flow on the inlet side of a positive displacement supercharger substantially, always requires a re tune or it will run lean. Since the misfire is coming after doing the air intake mods, its almost for sure running lean at high rpms and knocking. You need to throw a wideband air to fuel guage on it and check. If you can't do that, put the original air intake back on and verify the problem goes away.

You don't want to take your time messing around here, engine damage can happen, and might already have started to happen. A boosted lean knock is not the same as a properly fueled boosted engine running too much timing or poor fuel. The knock sensors can save those situations, but the knock sensors won't save a lean situation. Your pistons will just start swelling from heat until the ring lands let go.

 

[Doubeleive]

yep, need to backtrack to original airbox and see if the problem persist's if not then you need to have the tune modified for the induction system.
if the problem persist's with original air box/filter
then injectors are a known problem on the k2's, scan and diag.

 

[LSCALADE]

Here is a quick story around my adventures with the 5.3. I installed a AIRAID intake tube and you think its the same throttle body and same MAF housing and AIRBOX just the resonators are missing and no accordion tube. With the Airaid installed my LTFT were consistently running at about -4% LTFT. So that tells me its overreporting the amount it thinks is going in and the ECU starts off matching the fuel it thinks it needs and then it goes too rich and pulls some air back.
Swap the stock airbox and bam LTFT hover right at 0%. So in your case with your set up that change in intake tract is almsot certainly causing some sort of swing either Rich or Lean and if you got old spark plugs which probably have wider gap now than they did when they were new, aged wires, even and the coil is doing its best to send a spark but it cant.

Best path, swap back to the old intake see if it changes.

Any way you can share the HPT file of your callaway calibration, I am curious to see what all they changed compared to a NA 6.2L.

 

[hagar]

Lscalade: they don't change much, they are horrible tunes.

 

[randeez]

as others have said, if you have a decent scantool or hptuners do some data logging. can go back to the original intake and see if problem persists.
the new air filter/box/tube likely changed the airflow model enough to show it.
would also verify new plugs are correct ones and gapped correctly. not sure if calloway package drops down plug heat range but prob a good idea.
truck would likely benefit from full custom ecm/tcm tune in either case, whatever umph you were looking for with the intake could be achieved 2x/3x with a good tuner

 

[sealandsky]

Increasing the air flow on the inlet side of a positive displacement supercharger substantially, always requires a re tune or it will run lean. Since the misfire is coming after doing the air intake mods, its almost for sure running lean at high rpms and knocking. You need to throw a wideband air to fuel guage on it and check. If you can't do that, put the original air intake back on and verify the problem goes away.

You don't want to take your time messing around here, engine damage can happen, and might already have started to happen. A boosted lean knock is not the same as a properly fueled boosted engine running too much timing or poor fuel. The knock sensors can save those situations, but the knock sensors won't save a lean situation. Your pistons will just start swelling from heat until the ring lands let go.

You may be correct - But I really hope you aren't.

 

[sealandsky]

Here's a partial report from a scan and a pic of my intake mod. The funny thing is that the code it popped shows it was 64 miles back. But I had just run it at WOT and experienced the missing above 4,500 RPM steadily. For some reason it does not always pop a code.

 

[sealandsky]

as others have said, if you have a decent scantool or hptuners do some data logging. can go back to the original intake and see if problem persists.
the new air filter/box/tube likely changed the airflow model enough to show it.
would also verify new plugs are correct ones and gapped correctly. not sure if calloway package drops down plug heat range but prob a good idea.
truck would likely benefit from full custom ecm/tcm tune in either case, whatever umph you were looking for with the intake could be achieved 2x/3x with a good tuner

Please review the scans below. The original Callaway "Honker" CAI intake box was changed out because it sucked for filter changes and the mounting lugs had broken so I figured a change from a flat K&B CAI filter to a cone would be good (what could go wrong)? I really was not looking for more "umph", just convenience. The plugs were replaced last year and no issues until recently. Callaway has their own tune that is proprietary, so a full on custom may be all I could do if I don't want to go backwards.

 

[sealandsky]

I should also add (and maybe completely unrelated, but the timing of this is the same) but I've also been having some long cranking and rough running on cold starts lately. Some days are better than others, but a couple days ago it took to attempts to start, engine missing and sputtering, had to keep my foot in it as it was trying to die if left at idle power. It was also running on 6 or 7 cylinders for a minute and missing at lower power application until it warmed up.

Additional note: When I first completed the CAI filter box change, it ran great - For about 1 week. Then started missing and running crappy.

 

[randeez]

mass air flow showing .63 lb/hr should be more than that at 4800rpm
make sure its plugged in fully and in the intake tube the correct way - should be an arrow pointing at the engine

 

[Fless]

mass air flow showing .63 lb/hr should be more than that at 4800rpm
make sure its plugged in fully and in the intake tube the correct way - should be an arrow pointing at the engine

View attachment 484249

In addition, what's with the rich LT fuel trims? Short term looks okay, but you might reconsider resetting the long term trims to see if they continue to go rich.

 

[Doubeleive]

Here's a partial report from a scan and a pic of my intake mod. The funny thing is that the code it popped shows it was 64 miles back. But I had just run it at WOT and experienced the missing above 4,500 RPM steadily. For some reason it does not always pop a code.

that data is not what you want to look at it, I mean it is just for basics but what you need to see is knock retard, and individual misfire counts and maybe 02 sensor data. This needs to be looked at while in high rpm/under a load with the problem occurring in real time. (also during cold start as you noted that issue, I would guess that is injectors since these are a known issue on the k2's) The injectors on these could be misfiring hundreds of times and you would not feel it or get a code until it reaches a certain threshold
possibilities ? or things to check
injectors, coils, wires, high back pressure (bad cat's). high pressure fuel pump.
doesn't help that the tune parameters have been changed without tune adjustment.
there are not a lot of things that are going to cause the problem at least that I am aware of, I have chased this dog before...
basics are air+fuel+spark, one of those are the issue. unless you have developed a lifter problem.

If i go out and even adjust my CAI (it has a insert) it will throw a code, I do not get a driveability issue but these engines are pretty sensitive I also do not have forced induction. but I would imagine anything that is changed is amplified by a supercharger.

in this instance shown below, the DTC was already previously set, the misfire counts shown were not noticeable (sound wise), no rotational noise and would not have caused a code to set if I had cleared it previous to this instance, yet they show up with a scan. The outcome was bad injectors and it was a ongoing issue, in other scans the counts varied from a few to over a 1000 on either bank. It drove "ok" but was sort of a dog lacking power.

 

[randeez]

In addition, what's with the rich LT fuel trims? Short term looks okay, but you might reconsider resetting the long term trims to see if they continue to go rich.

I noticed that also, but my hunch is without the maf working, running 100% on speed density those tables werent dialed in real close in the tune.

 

[sealandsky]

that data is not what you want to look at it, I mean it is just for basics but what you need to see is knock retard, and individual misfire counts and maybe 02 sensor data. This needs to be looked at while in high rpm/under a load with the problem occurring in real time. (also during cold start as you noted that issue, I would guess that is injectors since these are a known issue on the k2's) The injectors on these could be misfiring hundreds of times and you would not feel it or get a code until it reaches a certain threshold
possibilities ? or things to check
injectors, coils, wires, high back pressure (bad cat's). high pressure fuel pump.
doesn't help that the tune parameters have been changed without tune adjustment.
there are not a lot of things that are going to cause the problem at least that I am aware of, I have chased this dog before...
basics are air+fuel+spark, one of those are the issue. unless you have developed a lifter problem.

If i go out and even adjust my CAI (it has a insert) it will throw a code, I do not get a driveability issue but these engines are pretty sensitive I also do not have forced induction. but I would imagine anything that is changed is amplified by a supercharger.

in this instance shown below, the DTC was already previously set, the misfire counts shown were not noticeable (sound wise), no rotational noise and would not have caused a code to set if I had cleared it previous to this instance, yet they show up with a scan. The outcome was bad injectors and it was a ongoing issue, in other scans the counts varied from a few to over a 1000 on either bank. It drove "ok" but was sort of a dog lacking power.
View attachment 484258

Thank you for your input and experience!