RPM limit under boost

[BlkSlvrdo129]

I'm having an issue where the engine won?t accelerate past ∼3000 RPM under part throttle or WOT acceleration, feels and sounds like hitting a fuel cut rev limiter.

In scan data I'm seeing differences bank to bank with injector pulsewidth and O2 narrowbands: B1 INJ PW goes as much as 4msec higher than B2 and B1 O2 oscillates rapidly while I'm hitting this rev limit. My wideband is in B1 and confirms B1 is leaning out slightly.
I've swapped injectors, coils, plug wires, plugs and NB02s side to side and issue still persists on B1.

A few observations I've made from my recent log:

• Issue occurs ⪆ 60% TPS
• Cyl. Airmass seems high at ≥1.5-1.8 g
• Inj. DC chart data is jagged, fluctuating ∼5%
• Fuel pressure is also jagged, fluctuating ∼10% (this is the most notable piece of scan data that makes me point towards a fuel delivery problem)
• Bank 2 O2 reports rich as expected ∼945mV
• Bank 1 O2 oscillates rapidly ∼61-888mV
• Inj. PW seems high at ∼25-29msec, in past logs without this problem I saw around 20msec or less for 5,000 RPM WOT pulls
• Inj. PW B1 goes higher than B2 during this issue, for example B1 28.0 vs B2 24.6

I cannot understand why this problem manifests on B1 only (fuel system is returnless and enters on the B1 rail so this may have a factor).
I'm leaning more towards a mechanical issue but in my scan log where I have the problem (time stamp ∼3:40 and 3.55) the PIDs Fuel Cut Torque Management Type shows Trans and Fuel Cut Type shows TqRed, so I'm unsure what influence these two parameters have on vehicle fueling; could one or the other command a fuel cut on one bank only, but if so I assume this would cut or modify the Inj PW signal (maybe the VCM scanner doesn't have the resolution to record this and I'd only see it on a scope?).

A couple closing thoughts, it's a stock fuel pump on a Silverado 5.3 with a TVS1900 so I expect to hit the limits of this pump but I assumed the data would show this across both banks, not specifically on one.
A few of the valvesprings on B1 have pressures that are ∼20lbs less than what were advertised new so I'm planning to shim those springs just to rule out a valvetrain stability issue.



081118-31 drive.hplNew injector scaling.hpt

[Lakegoat]

You are at 64%throttle, 146 MAP and you are still at 12.5 AF ratio. Are you sure that you have a 3 bar map sensor? And did you change your volts chart in the fuel injector section or just the flow?

[BlkSlvrdo129]

You are at 64%throttle, 146 MAP and you are still at 12.5 AF ratio. Are you sure that you have a 3 bar map sensor? And did you change your volts chart in the fuel injector section or just the flow?

I'm positive it's a 3-bar ZR1 sensor. So far I've only adjusted the IFR table since it's the only data I have for the injectors Magnusson included. I know the offset and PW tables need attention as well but I've gotten them to idle very close to stoich and WOT fueling has been close...and I was never planning on keeping them this long anyways.

[Frost]

What's the plug gap? It's clearly misfiring on bank1 based on that log. It could be spark blowout from incorrect gap, or just a cracked porcelain showing it's colors under the stress of load. -also, Cyl fill seems unreasonably high for 6PSI... either IFR or VE would seem to be off.

[BlkSlvrdo129]

What's the plug gap? It's clearly misfiring on bank1 based on that log. It could be spark blowout from incorrect gap, or just a cracked porcelain showing it's colors under the stress of load. -also, Cyl fill seems unreasonably high for 6PSI... either IFR or VE would seem to be off.

I took them out yesterday to check and they were .031, tightened them to .020. I'm fairly certain I gapped them tighter when I originally installed them but I'll have to look back to confirm.

Still had the same condition on the drive after re-gapping, maybe a little better, I'll go over the log more thoroughly tonight.

I agree with you about the cyl airmass, comparing to older logs without any problems I was around 1.19 at wot.

[lukearmstrong1990]

try disable transmission abuse in trans torque management

[BlkSlvrdo129]

try disable transmission abuse in trans torque management

I wasn't considering modifying that table because I've read cases people have had with negative unintended effects on GMT900 vehicles (weird timing retards, ABS and/or Stabilitrak issues, etc.,). HOWEVER, after reading the description in the VCM Help guide, specifically:

• Injector Disable Min RPM: Above this RPM, injectors will be disabled if abuse is declared
• Injector Disable Number: Number of injectors disabled if abuse is declared

I'm curious to know if the Fuel Cut Torque Management commanded from the Trans is disabling injectors on Bank 1

[BlkSlvrdo129]

Only changes I made in this log were to pull 9% fuel just before PE to help clean up a rich spot and it seemed like the length of time the fuel cut happens shortened and I was able to accelerate to 5,000 RPM.

Right now I'm assuming the trans torque management is commanding a fuel cut, 1 or more injectors are being cut on bank 1, which explains why the pulsewidth on that bank goes up almost 2-3 milliseconds with respect to bank 2; this enleanment is causing the stuttering/hesitation and shows up on the log as bank 1 NB O2 oscillating rapidly. I'm not sure why the fuel pressure would also oscillate at this same time, as much as a 10 psi swing.

I have all the fuel cuts disabled in the engine torque management tab(except for Powerhop, which I assume is unrelated in this case), so I may just halve the Abuse Mode tables just to see what effect they have.