5.3 Turbo Silverado Tuning Questions

[MG93]

Hello all,

This is my first post so my apologies if I missed some information that would help in discussing the issues I'm experiencing while tuning my truck.

I am in the process of tuning my 1999 Silverado and have finally decided to reach out to the forums for some help. The truck has a 5.3/4L80E, 78/75 turbo, Elgin 1840-P (228/230, .585"/.585", 112 LSA) with supporting mods, Summit 255 lph pump, and Snake Eater Performance 850 cc injectors. Snake Eater Performance supplied me with a data sheet specific to these injectors, and I've attached that to this post. I am running a 2002 Silverado 12212156 OS with the 2 Bar RTT custom OS applied, and have been driving the truck around trying to dial her in pure Open Loop Speed Density (no STFT/LTFT's).

This is kind of the backstory around the issues I have been having:

Originally, when using the injector data supplied by SEP exactly as delivered, I was having trouble getting the truck to idle at or near stoich, even when using the bi-directional controls (AFR override, moving absolute spark, IAC, etc). Something worth noting is that using that data I was able to run a conservative (well, pretty rich) AFR and make 10 psi on 9 degrees of spark, but the idle and cruise richness was seemingly not fixable in the tune (to my understanding), no matter how many iterations of VE tuning was done using the WB02 Error histogram.

I reached out to SEP and asked about the rich idle issue, and how my logged injector pulse width is around 1.8 ms while at idle, and that seemed kind of high for my setup. They said that it is common to lower the Injector Min Pulse Width in the Editor to 'the lowest value it will accept', but I felt that setting the IMPW to 0 ms would be ill-advised. So I cut the supplied min pulse width value (0.795876 ms) in half, and reduced the Min Fuel Milligrams transient fueling factor by the same amount. With these new injector settings, I was able to start the truck and actually use the bi-directional controls, specifically the AFR override, and drive the idle AFR down (the fueling was much leaner now, like 18 ish) to any value I wanted, even richer than stoich. So I used the VE RTT to get the cells my truck sees at idle to within 2-3% error, and also gave the rest of the table about 10% extra for some cushion.

All was well as I drove the truck to dial in part throttle and cruise, and I got some good data taking it easy on the way to my destination. Upon leaving I flashed a new tune with the WB02 Error values applied to my VE (mult, % - half). So at this point, presumably since the truck was hot and had sat for about 30-45 mins, it started, stumbled rich, then recovered, the took off lean until it stalled. I sat there messing with it for a while, giving the Base RAF, P/N table more air, 0.5 g/s at a time. I also messed with the Startup Airflow Delay and Friction Airflow Decay tables and managed to get the truck to start, but not well. I have the Russ K idle config histograms and channel setup, but I'm thinking that the lean take off issue is something else that I did, and I'm not sure. The truck pretty much does this same stumble and lean take off when I try to start it, unless I increase the Friction Airflow Decay and Initial tables quite a bit. I think this is the wrong approach.

Lastly, the other thing that's happening is when I do manage to get the truck started, it recovers from the start and idles at around 16 AFR, and SLOWLY tapers down to stoich, unless I begin to move the truck. Conversely, when I am driving and come to a stop, the AFR will hang rich (like 13.5ish) seemingly indefinitely, whether on the brakes in gear, or switched into P/N. I have adjusted the VE in the idle cells already, and the converse scenarios of hanging lean or hanging rich as previously mentioned makes me think this is something to do with the idle air controls in the PCM.

I have attached the current tune, and a log file from a time when it started, stumbled, then took off lean until stall, and another where the idle AFR slowly moves toward commanded (stoich) after recovering from the startup flares. I also attached a log of how the truck idle AFR would hang rich when coming to a stop (seems to be whether in gear or when switched to P/N), until I blip the throttle. Lastly,

I should note that I do have a mechanical fuel gauge on my rail instrumentation port and would see 58ish psi KOEO, and the same at idle, but when the engine (and presumably pump and fuel) are at operating temp, the fuel pressure would drop to the value shown in the attached picture. (around 45ish psi). I am waiting for my digital pressure transducer to come in this week and I will be using the 0-5V EGR supply and input to PCM to log it, hopefully providing more insight to what's happening under load. (stock fuel rail and boost referenced FPR).

20-11-23 16-45-02 hot start stumble then lean stall.hpl
20-11-23 16-58-46 starts lean then taper to stoich.hpl
20-11-23 17-02-25 drives fine then rich when stopped.hpl
99Z71_02OS_2bar_112320 VE2.hpt
SEP850_Multec_JUL20.xlsx
IMG_20201120_104408.jpg

[MG93]

My apologies for the long initial post, is there any other information that I should provide? Kind of chasing my tail here. Thanks!

[chopperrudy]

pmd.

[MG93]

Hey chopper, I just replied to your PM. My issue was heat soak after of the IAT sensor after running the truck up to temp, and trying to start it after messing with the tune in the truck and flashing it for five to ten minutes. Disable Complex Charge Temp and add 100 camshaft rev's to your Startup Airflow Decay table. I also cut my Min Injector Pulsewidth in half to gain more control over my idle fueling.

[chopperrudy]

Thanks for the info