Troubleshooting lean spikes on large throttle transitions
Thread Starter
Launching!
Joined: Aug 2015
Posts: 206
Likes: 11
From: Duvall, WA
Troubleshooting lean spikes on large throttle transitions I'm sure something like this has already been covered in depth somewhere in here before, so feel free to just link me to the relevant thread(s). 
Engine management setup:
HP Tuners MPVI Pro
GM P59 ECU, drive-by-wire, basically complete 2005 GMC Yukon engine controls
2-bar SD operating system based on a 2005ish manual transmission 4.8L truck
GM IAT (no MAF) about 6" in front of throttle body
Injector Dynamics ID725 injectors, correct constants entered into the tune (for constant ~4 bar deltaP, see comment about FPR below)
Dual Walbro GSS342 pumps, -8 AN feed, -6 AN return. Second pump on low-pressure Hobbs switch, first pump always runs full speed
Engine:
370 ci LQ4/9 derived engine
~9.5:1 CR
PRC 225 as-cast cathedral port heads
TSP 228/232, .600", 114 LSA + 3 cam
LS6 intake manifold
LS3 Camaro exhaust manifolds
Turbonetics T-Series 7875 .96 A/R T04 turbo
Very free flowing exhaust after turbo
Manual transmission (T56 Magnum)
Symptoms: On rapid throttle transitions, such as you might encounter when shifting the car quickly, there is a major lean spike reported by my wideband O2 sensor. It sometimes causes a misfire that can be heard and felt. It is possible to do this by whacking the gas pedal at idle.
To the best of my knowledge, the car is correctly tuned for steady state operation. I don't have any big "holes" in the VE map, fuel trims are typically <5%, and the car tracks close to target AFR at WOT.
Possible quirks in the tune:
- I'm running a pretty late end-of-injection timing to reduce fuel short circuiting with the cam.
- Burst knock retard is effectively disabled
What I've tried:
- Disabling DFCO by setting the temperature thresholds really high.
- I played with the two transient fuel tables I can see (which appear to be gain tables, not the actual impact table) but it didn't seem to do much.
Suggestions are welcome.
Engine management setup:
HP Tuners MPVI Pro
GM P59 ECU, drive-by-wire, basically complete 2005 GMC Yukon engine controls
2-bar SD operating system based on a 2005ish manual transmission 4.8L truck
GM IAT (no MAF) about 6" in front of throttle body
Injector Dynamics ID725 injectors, correct constants entered into the tune (for constant ~4 bar deltaP, see comment about FPR below)
Dual Walbro GSS342 pumps, -8 AN feed, -6 AN return. Second pump on low-pressure Hobbs switch, first pump always runs full speed
Engine:
370 ci LQ4/9 derived engine
~9.5:1 CR
PRC 225 as-cast cathedral port heads
TSP 228/232, .600", 114 LSA + 3 cam
LS6 intake manifold
LS3 Camaro exhaust manifolds
Turbonetics T-Series 7875 .96 A/R T04 turbo
Very free flowing exhaust after turbo
Manual transmission (T56 Magnum)
Symptoms: On rapid throttle transitions, such as you might encounter when shifting the car quickly, there is a major lean spike reported by my wideband O2 sensor. It sometimes causes a misfire that can be heard and felt. It is possible to do this by whacking the gas pedal at idle.
To the best of my knowledge, the car is correctly tuned for steady state operation. I don't have any big "holes" in the VE map, fuel trims are typically <5%, and the car tracks close to target AFR at WOT.
Possible quirks in the tune:
- I'm running a pretty late end-of-injection timing to reduce fuel short circuiting with the cam.
- Burst knock retard is effectively disabled
What I've tried:
- Disabling DFCO by setting the temperature thresholds really high.
- I played with the two transient fuel tables I can see (which appear to be gain tables, not the actual impact table) but it didn't seem to do much.
Suggestions are welcome.
Last edited by lemming104; Jul 12, 2018 at 10:39 AM.
Thread Starter
Launching!
Joined: Aug 2015
Posts: 206
Likes: 11
From: Duvall, WA
Thanks. Based on what a quick web search turned up, I should set "Fuel->Power Enrichment->Enable Torque" to a lower value to prevent torque calculations from interfering with PE, and "Torque Management->General->ETC TPS Max" to 100s to prevent it from overdamping the throttle? The torque limit spark retard stuff is all set to zeros, so it shouldn't be trying to truncate torque via spark retard. I don't think I saw anything blatant that could cause a spark-related misfire (like lots of spark retard on tip-in) in my logs.
Anything else?
Anything else?
