2008 GMC 6.2L - Detonation at Idle
I'm looking for input on a strange issue I've really never seen before.
The vehicle listed above has a little over 200,000 miles on the odometer and appears to have been well maintained. The problem with this vehicle is that when the engine is at normal operating temp, at idle, in gear with the A/C on, the engine will begin detonating. There are no issues under a normal drive. No DTC's set. Fuel trims look fine (+10% LTFT).
Here are a few images of scan data so you can see what I've discovered thus far:
Initial log at idle with active knock retard.
Initial log at cruise under normal load (Didn't log KR but you can see final spark doesn't indicate KR activity)
On a SWAG I decided to see what would happen if I added propane and discovered that the detonation went away temporarily.
That had me thinking that fuel quality might be an issue. After checking FP/Volume and Alcohol content (~7%), I decided to run the vehicle off an injector cleaning fuel supply and experienced no change.
I decided to log KR per cylinder to see if the issue was isolated or not and found that it wasn't. This image has cyl's A-F from top to bottom on the right.
I thank you in advance for reading my request for assistance and appreciate your input.
Scott, I do not see a load pid on your capture, but I do notice that the throttle percentage appears to be quite high for idling in gear. I have experienced this condition on a 4.2l Trailblazer with a partially locked up torque converter. The key was the load would increase significantly when changing from park to drive or reverse. HTH
Hi Mark, That was my thought. I've experienced a torque converter fault on a 2014 G-1500 with a 4L60E that detonated at an idle. Scott, Can you take a capture of Engine Data in Park/Neutral and then when shifted to Drive, with the Tech 2 and post the file?
I’ll capture some more data in the AM but not with the T2, that’s a PITA.
I thought I saved the snapshot, but I can't find the sur file right now. It was a 2013, not that it matters all that much. VIN 1GCSGAFX5D1146585 From my notes - When the vehicle was in park the throttle angle was 14*, the load was 34%, the MAF sensor was 5.1 g/s, the injector pulse width 4.2 mS, the torque was 9.6' lbs. I did not record the MAP... When the vehicle was shifted into gear the…
Thanks Scott, Yes this one has a converter clutch that's staying partially applied. I replied to my original message with a video showing a lot of the data metrics requested. For numbers sake here's what I observed this morning: Idle in neutral: - RPM: 595 - TP: 17.6% - ABS Load: 15.8% - Cyl/Air: 0.15 grams Idle in gear: - RPM: 553 - TP: 23.9% - ABS Load: 34.1% - Cyl/Air: 0.32…
Thanks Mark, didn’t think about the TC, I’ll look further into that in the morning. The 3rd capture has absolute load at 32.9%. I just checked and found data I recorded on this vehicle about 8 months ago and have the following absolute load numbers: Idle in Park: 15.7% Idle in Gear: 22.7% Btw, one can calculate abs load with MAF and RPM to determine cylinder air mass and divide that by 100%…
I am not claiming to know whats wrong with this truck. But I have a few questions. Is the oil new and full with correct filter? Has the TB been cleaned and idle learn been done? Can you watch the actual and desired VVT position when its detonating and see if the actual is keeping up? Also see if the VVT duty cycle goes crazy when this happens. You can also command the VVT to 0 when this happens…
Thanks Caleb, Yes the oil and filter are correct and full. Oil pressure tests were performed as well. The throttle body has been cleaned and idle relearned. I’ll be looking into this challenge more tomorrow and I’ll report back. Thanks again for your input.
I agree with the suggestions that you appear to have a parasitic load situation. Having not experienced the torque converter issue that was brought up, my first inclination would be to inspect the belt drives thoroughly. Ideally, removing the belts and physically inspecting everything to rule that end of the engine out before moving to the back side. Whichever end is causing the excessive…
Thanks Nathaniel, I’ll check into that further. When I first drove the vehicle I noticed the noise from behind the wheel sounded like the compressor was the culprit. After going all over this thing with a stethoscope, the noise was not coming from the compressor but that doesn’t mean the compressor is off the hook. I’ll collect some more data tomorrow.
You mention previous captures. What was the IAT in them? Have you a WPS?
The vehicle has a stock air box and fresh air is isolated from the underhood environment. The IAT was between 33 & 44C. Yes I have a WPS.
That IAT you are replying with is from the previous capture you mentioned? Do you feel the scan data accuately represents the engine's condition as well?
Hi Spencer, Confidence is high that the data is accurate in both the previous captures and current data.
Thanks for the reply Scott. Nice job on you and the group for pulling this one through the mud and finding the issue! I also think you found an area that GM didn't spend much time at all make the LIT(lead ignition timing) tables what they should be. Kinda good they didn't eh or you might not of seen what you saw where you saw it. Thanks for a good thread and all the efforts.
Yes I’m very thankful for everyone‘s support. I don’t believe that it’s the spark tables but rather the size of the combustion chamber. I did take a close look at this vehicle including what you‘re referring to. �
Which would be calibrated if they checked it in the same loaded conditions you had this vehicle in. Just my take on it. I have seen quite a few sloppy OE tables that seemed to be overlooked as if they didn't think it would ever go there. Now if you are considering your combustion chambers are a bit different due to the mileage on this from carbon I could mayber entertain that but feel it would…
Spence, It would be fairly convenient for the OE to fine tune that part of the calibration on an engine dyno. I would agree that the opportunity was there. I just wonder if there was an other limiting factor. They could only do X throttle opening etc. to maintain emmissions, or limited within he program. I will look at the program later on.
Hi Bill good to hear from ya! I agree the opportunity was there. As far as emission... Having spark knock I feel would raise NOx.
Thanks Spence, Good to see you here. I am interested to see what your thoughts are. I started another post to springboard off this post,and keep the content in this one about the original concern and resolution. I agree, I was spitballing. Sometimes there is some unexpected limiting factor that the engineers were bound by, that we don't understand. That is what I was trying to get at.
Hi Spencer, My thoughts dwell on the volume and shape. Sure, carbon could be factor as well but I did try commanding the spark as low as 8BTDC and it had no effect.
If I am reading what you are saying correctly... I don't feel the volume or shape has changed since the engine was built. Except for wear or carbon build up that engine may not of needed the amount of lead timing since new. Just my thought for what it is worth.
I'm thinking more along the lines of a large bore cylinder at slow speeds with that much cylinder fill isn't seeing a very homogenous mixture to support a proper combustion event. I believe that adding propane may back that claim up. As I said, I tried moving the final spark around and had no effect.
Duly noted Scott. Don't know as I would agree yet but thanks for the reply. Have a great day!
No problem, It‘s a working theory.
Scott, What do you think is the limiting factor from the program eliminating knock with the size of the combustion chamber? Would you mind showing the tables and sharing your thoughts? I should be spending more time looking at the tables, and this is a fun one to do that with. Did you ever try dialing back the timing during the condition through other means?
Hi Bill, This is what I wrote above to Spencer: "I'm thinking more along the lines of a large bore cylinder at slow speeds with that much cylinder fill isn't seeing a very homogenous mixture to support a proper combustion event. I believe that adding propane may back that claim up. " I read this with EFILive. If you want a copy of the cal let me know and I can send it. Here is the Idle Spark…
Thank you Scott, Do you feel continuing down this discussion is relevant to this post? I was downgraded with an off topic tag earlier on. Maybe continuing this discussion should be in another thread? I felt the converter was the what of the detonation, and the program/bore size was the why.
Starting up a thread and referencing this one makes sense. I’ll let you begin the discussion.
Hi Nathaniel, Great suggestion on the use of a thermal camera. This morning I recorded additional data others like yourself recommended and here is a short excerpt of segment where I recorded the torque converter temps: In gear at idle following by a 8 minute idle cool-off in neutral. It's clear to me that there's a substantial amount of friction taking place within the converter.
Excellent find Scott! That torque converter is hitting trailer-towing temperatures, just at an idle in gear. Thank you very much for taking the video and posting. That's going to be a GREAT reference for this type of issue, going forward.
That is neat. I have seen issues of drag cause this in videos etc. Never seen it in the bay. Sounds like a diesel running. GM has TSB's on the TC causing this. Be great to have a video. Seems that you were able to cool combustion with the propane. I wonder if you can command timing back during the condition. I have a funny way of thinking about things. I am more interested in the science behind…
Hi Bill, I'll record some more data on this today and report back. I just looked back through my data and I see that I have some data that I wanted to use in a case study but never got to it. This vehicle BTW had a P1174-00 / Fuel trim cylinder balance (bank 1) code last year that was resolved by replacing the injectors. When I road tested the vehicle before and after I noticed the HO2S…
Thanks Scott, During the condition ignition timing doesn't seem out of line with the norm. With cyl air and map pressure higher, I am assumming the program is using timing to control idle as the authority, and it was never designed or tested within that load range at a low idle. Looks like a pretty dense air charge. I am racking my brain on how to induce a load safely to "play" with this…
Hi Bill, Good thoughts. I'll have to think about this some more, but... I wish I could find the files on my vehicle, but with what I had noted, there's more going on than meets the eye. I think having a 5 gas analyzer could pick something up, but looking at Scott's H2OS it does not appear to be a fueling issue. My pulse width more than doubled, so you would think it has enough fuel? The load…
Scott C, I am getting degraded ratings for discussing the detonation part past the what... I feel the converter was the what and the program/large bore is the why. I felt it was relevant to this topic, but maybe it is best discussed elsewhere. I have input, but I do not want to muddy this topic if it should be discussed elsewhere.
Hi Bill, Um, if we can't discuss the why on the same thread on a place called diag.net (I'm figuring short for diagnostics. (:-) we might as well jump on the Yukon Forums and discuss it over there. I'd agree that there's probably a maximum correction that's built into the software, but I believe this has to do with a drastic increase in heat due to the increased "load" on the…
I agree, I am not sure why I and others were being downgraded for discussing the detonation. There was no comment on why, just a downgraded mark and "off topic" tag. I see the downgrades have since been removed. I can see if someone wanted to keep subject matter cleaner. I agree. If you want to bounce over to the detonation discussion I appreciate your input. Thanks Scott
As of this posting I still see three on my name for whatever reason. Bill I don't want to distract from an awesome group effort and finding a tough problem so quickly by a narrow minded person(s). Detonation was what was a huge part of this discussion and to think your comments or mine for that matter were anywhere off topic is as mentioned narrow minded. Guess that's my welcome to the group…
Sounds like an unwanted load? What is the injector pulse width? Torque converters do some strange things to line techs. Did the propane just cool the cylinder to negate knock retard? Just questions that come to mind as I view the data.
Maybe I missed it but have you explored an overcharged AC system or compressor fault causing the higher than normal idle load?
Hi Rusty, Thanks for your input. I'll be collecting some more data this morning and will report back.
As suggested try taking the belt off to eliminate the A/C compressor or an overcharge condition. Or just turn off the A/C and see if that makes a difference.
There was a help post recently on iATN that dealt with a 2013 Suburban 5.3L with a pinging/detonating issue. It ended up being a faulty torque converter, broken stator I believe. members.iatn.net/techmail/view…
Thanks goes out to everyone that provided me with the additional guidance leading me to a conclusion. It's clear to me that the torque converter clutch is staying partially applied. I recorded a video that includes many of the requested data metrics. The use of the thermal camera was quite eye opening and after seeing those temps and having a look at the trans fluid condition we are going to…
I was discussing this post with my coworker that builds transmissions at our shop. Not sure if anyone suggested it yet but the ones we have had here at our shop have plugged up the trans cooler and are unable to be flushed completely clean. He sells the radiator and an external cooler. Here is some pics from one. That is the screen on the flush machine after 2 flushes. Just a thought.
Thanks Chris, I appreciate the feedback and suggestions. We found that the transmission on this vehicle was rebuilt a while back and is still under a repair warranty. We'll work with the trans shop and stay in the loop on what they find.
Cool! Nothing like hearing the noise for myself to remember it. What is that tablet A/C analyzer set-up you have going on there? Never seen or heard of anything like that. Never seen that laptop scan tool either, but it said "tuner (something)" so that mystery is solved.
The A/C Set up is ManTooth device from Ritchie. The scan tool, don’t try one or you might start hating the common tools available today.
LOL Scott thanks. You forget what I work on out here. OBD2 generic is good enough. I tried a laptop scan tool five years ago and it was impossible to deal with. We don't have the floor space to roll (or store!) a fancy cart like that. Your hoist is nicer than any car I have ever worked on. That "ManTooth device from Ritchie" is really neat! Thanks.
Yes, generic OBD is where most of the action is yet most tools make it difficult to access, even OEM tools.
HP Tuners scan software is really fast as well, i like the scan software, just not as convenient as a scan tool at time, but defiantly worth the money, especially if you dont need credits or tune
I agree, the tool is as valuable as you make it. Learn to leverage the ability to display the data you want to see and in the units you prefer. Some of these tools will allow you to record in one unit and then limit the unit choices when viewing the recording, very puzzling. Additionally, some parameters that are not available in the OEM tool, but are available in these tools. For example, take…
What part of the Hp tuner software are you using? i have the basic one that i can do some programming with like turn off 4 cylinder mode, speed limiters, etc. I realy like the graphing on that and the function testing.
You are not programming when turning off cylinder. You are using activation testing part of the software.
VCM Scanner mainly. We've seen some retro rod vehicles that needed some help in the past. I had a Roush mustang in recently that another shop brought in because the monitors would never complete. I suspected that the ECU had been modified and used the EDITOR app to read the ECU to confirm.
Bang for my buck, the best money I ever spent was on this, 12 years ago, still ahead of almost every MMY I see here;
Hands down you'll hate them as well as the powertrain part of the factory tools. ;)
Awesome find. Digging the scanner. Does it have a good amount of bi-directional controls. Snap on and autel have good bi directional, but their global data list sucks. I never have but a couple primary I always go in under ymm.
Hello everyone following this vehicle issue. I'm happy tor report that the vehicle returned from the trans shop today fixed! Here’s a short video for demonstrating the neutral and drive load numbers with and without the A/C on.
Nice job Scott! IAT was even higher then the pre trans service capture. Load was a bit lower as well. Thanks for taking the time to update. Again nice work.