DBC LQ4/4L60E "Limp mode" after 1st 1-2 shift

[Fast4.7]

I have tuned a lot vehicles and never seen one do this before. Truck drove well on the tune I was working on then suddenly lost all throttle response, PCM is acting like it is in a limp mode of sort and will retard the timing advance and starts reducing fueling on its own at steady throttle opening causing it to lose power. No code other than P0102/103 because it is speed density. Will also add that this truck killed an 0411 mid drive a few weeks ago. Starting to feel like it has a harness issue. We were driving down the road, started doing the same thing and the PCM stopped communicating with the scanner. Pulled the PCM and I could not even communicate with it with my bench flash harness. Started over with a 2nd PCM, runs well until that first 1-2 shift again. I am at a loss.

Truck is an old C10 swapped with a LQ4 6.0L, Sloppy Stage 2, Stock 4L60E, Mid-rise aluminum intake, 102mm throttle body, shorty headers, and 4.10 gear. Ran extremely well prior to whatever PCM or Harness gremlin exist now. Tune file is correct for the injectors and fuel system as well. Everything obvious to me has been covered. Open to opinions on anything I have missed somehow.

[Fast4.7]

Truck is speed density and open loop. I had my LM1 on it when I tuned the VE tables a few weeks ago. Whatever is happening with the PCM is right after the 1st 1-2 upshift. After the 1-2 shift the pedal is basically dead. Give it throttle and it goes dead lean because the PCM is drastically cutting the injector pulse width. If you stay on the throttle loses more and more power, can watch the PCM continue to pull the pulsewidth lower.

Franks C10 6.0L Speed Density COS Fresh Start.hpt

Franks C10 Limp Mode 2.hpl

[SiriusC1024]

Loose mounts shaking a weak ground somewhere?

[abc]

What voltage is the PCM reporting?

[Fast4.7]

Loose mounts shaking a weak ground somewhere?

Did a good shake down on everything, nothing out of place that I could find. Good solid connections at the engine. Mounts are good.

[Fast4.7]

What voltage is the PCM reporting?

14.2 cold start and about 13.2-13.5 driving. Normal GM alternator output.

[SiriusC1024]

Accel coils?

Only thing really that could kill an ecu is the coil packs. Maybe one has a problem? There is snubber circuitry that can fail. Does dwell time in the tune match the coil type? Copper plug wires (MSD super conductor bs) instead of graphite (Taylor) don't help, either.

[Alvin]

I'd check fuel pressure. A cable throttle body GEN 3 doesn't have a limp mode that I'm aware of.

[Fast4.7]

Turns out it was fuel pressure falling off under load. Still does not explain the RH bank injector pulsewidth dropping off repeatedly. It no longer falls off in the test drive today and the truck has plenty of get up and go. That being said runs great now with good fuel pressure. I also could not think of anything in a DBC that would make it respond like it had a limp mode, hence why I put quotations around the words. Hopefully the failed 0411 does not repeat itself in the future. That being said after updating to the newest Beta version of HPT my MPVI started working again too. So now I have 2 working HPT Interface devices. My 2011 Pathfinder is now mostly dialed in since I picked up the MPV3 too. Pathfinder is running better than ever too. Thorley long tubes going on it soon, on a bone stock 4.0L they gained 28 ft/lbs @ 3,500 rpm and 26 hp and 23 ft/lbs peak to peak when a prototype setup was tested back in the day, good increases for an otherwise stock V6 and mine has additional airflow increasing mods. With the AC on the old 4.0L, pulled a sub 7 second 0-60 with minimal wheel spin. Good news all around. Tomorrow I finally dig into the 383 in my Express van to swap to the custom Erson cam and put the Holley intake manifold I have for it on it along with the 103mm MSD throttle body.

[SiriusC1024]

Oh I thought when you said reduce fueling that IDC was being commanded lower for some weird reason.

[Fast4.7]

Oh I thought when you said reduce fueling that IDC was being commanded lower for some weird reason.

It was getting reduced IDC. Sorted out the lack of fuel delivery causing reduced fuel pressure and it went away on its on. The lower DC on bank 2 is still a mystery. You can clearly see it in the log I attached.

[SiriusC1024]

Reduced fuel pressure would mean increasing IDC though.

[Fast4.7]

Reduced fuel pressure would mean increasing IDC though.

Should not change anything. OLSD Tune. I would have used a MAF and narrowband 02s on my vehicle, but I did not set this one up. Just had to tune what is there. I had my LM1 dual bank wideband sensor kit on it when I initially tuned it.