Abarth500.

Hey yall! New member here, sorry for creating a thread so early on, but my warranty expiration is creeping up on me fast and I need to get this sorted- so here's my issue.



I have a 2015 2500HD with the 6.0 and about 95,000mi, and for the past 6 months, I've been having this issue where It'd start pulling timing ( up to 15 degrees of KR) under moderate to heavy throttle, as soon as it hits 3000RPM. There is no audible knock, but 15 degrees of KR sounds very excessive. Higher octane fuel makes the issue better, and usually after long interstate drives (no heatsoak), it runs great, but generally, it's very bad. Towing a 32FT trailer full of band equipment up a mild hill, it struggles to get out of first gear, and slams into the next gear because the timing is so far retarded before the shift, that it screws with the shift timing. I have used various fuel system cleaners ( now trying Amsoil Pi, as I know its well proven ) but so far, none have made any difference. I want to check the fuel pressure, but I don't see a test port, and I can't get any OBD app to display fuel pressure.



Here's what confuses me: Sometimes, under the same conditions, It'll run just fine and pull hard straight through 3000 RPM. The only thing I can find different between the times that it runs like a POS and times that it runs like its brand new, is that when it's running like crap, it shudders at idle- enough to be felt throughout the entire truck.



It pulls the most timing at around 3000, and tapers down as the revs increase.



I got it used, with about 76,000mi, so I'm not clear about its past. Back when it was running horribly I was considering that It might have been tuned by the previous owner, but lately, its been randomly running just fine.

Its been fine for the past week or so, but I'm still very curious about what could be going on.



I have TorquePRO recordings of the issue happening, which I may upload later if that would be of any help. I've been hoping for a CEL but of course- no pending or stored codes!



Thank you all! Sorry for the length of the post!

Abarth500.

bump... Still confusing me

FFDP

iTrader: (2)

The fuel pressure test port is on the fuel rail, sometimes it's just a bard on the passenger side if I remember right.

Without a data log I'm not exactly sure what is going on and what it's going what it's doing.

If anything you could unhook the battery for 30min, unhook both cables from the battery so there is no power going to anything, then touch the cable ends together. This will remove what they call the "volatile memory" and do like a full reset. Then connect the red terminal and then the black, fire the truck back up.

Abarth500.

Thank you for the help. I did check for a pressure test port but couldn't find one, I'll check again. My old 5.3 had it right on top of the passenger rail but I can't find it on the L96.

Here are some runs I did while towing. I don't usually accelerate this hard with a trailer, but its a good example of what it's doing.

On the first run, I kept my foot in it, on the second run, I eased off as it began to cut out, which actually results in the truck accelerating quicker. If I let off the gas slowly while it's pulling timing, it actually gets to a point where it stopps KR and just takes off like nothing is wrong.

Run 1
https://youtu.be/ChS1maDlX8g

Run 2
https://youtu.be/CAEOmPsneZw


As far as the ECU goes, I've done all of the tricks I know- leaving it unplugged overnight, touching terminals, cycling ignition with battery disconnected, and even unplugging the ECU harnesses.

Thanks much!

madmann26

iTrader: (7)

It's been pulling timing the whole time.

Depending on the ECU, it's normal and it sounds like burst knock, IAT and ECT pulling timing all at once or a combination.

You need a tune to fix it right.

Abarth500.

Even if it's 70f ambient and it's full of fresh 93 octane, it still does it .

Very rarely it'll run like nothing is wrong. It doesn't feel like it should ever run like this- any throttle over 60% and it just stopped accelerating all together, even without a trailer.

I started datalogging because there was a really obvious issue with how it was running.

Is it possible a temperature or knock sensor is bad and giving false readings?

madmann26

iTrader: (7)

Yep,

The truck tunes are very conservative from the factory. On the gen3 trucks, burst knock kills us.

The e38 pcm has burst knock, ECT, IAT that can affect timing based on load/RPM/temp. It also adds valve tempurature, driver demand, etc.

There are a lot of tables that can pull timing back.

What you describe sounds like burst knock but without a decent scanner, it's hard to pinpoint.

FFDP

iTrader: (2)

His truck will actually be the E78 which uses an even more advanced logic compared to the E38. Could even be a torque based limiter in his too.

Abarth500.

It's like hitting a wall at 3000! Lol

I have an OBDLink MX and Torque Pro, DashCommand, and the MX app. I'm not very experienced with GM PCM/ECU stuff- but I'm somewhat proficient with Fiats ECU setup, and I love to learn new things, so I should be able to catch up pretty quickly.

What all do I need to log? I'll jump on that as soon as I can.

Abarth500.

If you watch the videos, I forgot to mention that 80% of the time, it behaves like the First Run with 0.0 KR until 3000.

Only sometimes, after being heatsoaked, will it KR off of idle (which I expect in that case). The interesting thing is that when it's heatsoaked and pulls timing from idle up, it pulls less timing over all than if it stays at 0 KR until 3000.

(I could be very wrong about this next bit..I have no idea what I'm talking about)

Possibly because it's switching to the low octane map and doesn't command much timing advance in the first place?