Anyone here proficient with GM ECUs?

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Jonohhh
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Joined: Thu Sep 20, 2018 12:14 am

Anyone here proficient with GM ECUs?

Post by Jonohhh » Fri Nov 02, 2018 12:27 am

I'm having an issue with my dad's 2015 Silverado 2500HD with the L96 6.0, and I'm trying to fix it for him but I'm a bit perplexed about what's going on.

I'll save the wall of text until after I know if anyone here can help. I made a post on a GM forum but between me being a brand new member, and not having common tuning software like HPTuners, I wasn't getting very far.

Jon

nightowlracing
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Your Car's Year / Make / Model: 03/Mitsubishi/Lancer Evo 8
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Re: Anyone here proficient with GM ECUs?

Post by nightowlracing » Fri Nov 02, 2018 8:11 am

What codes are being thrown if any? What exactly is going on because asking for help with a problem without telling briefly what the problem is pretty difficult to figure out.

Jonohhh
Posts: 45
Joined: Thu Sep 20, 2018 12:14 am

Re: Anyone here proficient with GM ECUs?

Post by Jonohhh » Fri Nov 02, 2018 9:54 am

Thank you, NOR. Here yah go.

So here goes, and when I have more time, I'll go back and add detail.

Basically, at 3000+RPM at moderate to heavy throttle, the ECU pulls a ton of timing, up go 15 degrees of knock retard. So much KR, in fact, that it absolutely screws with the transmissions power management during gear changes and causes it to sometimes slam into the next gear, or even flare.

Changing fuel octane doesn't do anything, and there is no audble knock. Usually runs fine at lower revs, but when it hits 3000 its like hitting a wall- there's a jolt as the engines output suddenly drops off.

Now, sometimes it runs like nothing is wrong and it feels great, usually when the intake is cold, but if it's more than 70 degrees or has had any time at all to heatsoak, it runs like absolute crap.
I can't stress this enough- this is not normal behavior.

Other than that, it just feels unsteady under heavy loads, with totally random fluctuations in engine output. No codes, unfortunately, just went out of warranty.

2015 2500HD with the L96 6.0, 6L90 trans, and about 100,000k miles.

I've changed plugs, tried different fuels, unplugged and cleaned MAF, unplugged O2s, and cleaned the throttle body. None of those made any noticable difference.
Last edited by Jonohhh on Fri Nov 02, 2018 11:16 am, edited 1 time in total.

nightowlracing
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Re: Anyone here proficient with GM ECUs?

Post by nightowlracing » Fri Nov 02, 2018 10:09 am

Like you mentioned without having an hptuners cable and everything you can't really see where to point your finger as to what the root of the problem is. Looking at it blindly I would imagine IAT sensor but that is a shot in the dark without having hptuners to datalog the problem.

Jonohhh
Posts: 45
Joined: Thu Sep 20, 2018 12:14 am

Re: Anyone here proficient with GM ECUs?

Post by Jonohhh » Fri Nov 02, 2018 11:22 am

I've changed plugs, tried different fuels, unplugged and cleaned MAF, unplugged O2s, and cleaned the throttle body. None of those made any noticable difference.

I added this to the original post to help out future readers, but I'll definitely check out the IAT signal from torque pro.

I know there's not much info to work with but thank you for your input.

Jonohhh
Posts: 45
Joined: Thu Sep 20, 2018 12:14 am

Re: Anyone here proficient with GM ECUs?

Post by Jonohhh » Fri Nov 02, 2018 3:34 pm


Jonohhh
Posts: 45
Joined: Thu Sep 20, 2018 12:14 am

Re: Anyone here proficient with GM ECUs?

Post by Jonohhh » Fri Nov 02, 2018 3:37 pm

So, this is what it's doing, as seen through torque pro. Keep in mind, this was towing a 32ft trailer full of marching band equipment, so I don't expect it to be fast, but you can definitely see what's going on at 3,000 RPMs.

nightowlracing
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Re: Anyone here proficient with GM ECUs?

Post by nightowlracing » Fri Nov 02, 2018 3:40 pm

Need to log IAT's from cold to operating temp as the problem happens.

Jonohhh
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Joined: Thu Sep 20, 2018 12:14 am

Re: Anyone here proficient with GM ECUs?

Post by Jonohhh » Fri Nov 02, 2018 3:58 pm

Great, I'll get on that. Thanks.

Jonohhh
Posts: 45
Joined: Thu Sep 20, 2018 12:14 am

Re: Anyone here proficient with GM ECUs?

Post by Jonohhh » Sun Nov 04, 2018 11:09 pm

I still need to log it properly, but looking over it while I was driving, the readings seem normal. With 64f ambient, I saw 73 after idling for a few minutes, and 67 during a short pull.

Ill see if there's a certain temperature the issue actually begins at when I log it.

It can go from driving fine to cutting out completely randomly within a drive cycle, sometimes going full circle within a minute.

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