I am building a rock buggy with an 8.1L from an Avalanche 2500. I have built the motor and fired it up fine. Just starting to work on tuning the motor. I am only playing with the idle range as the motor is basically sitting in partially completed frame.

With the stock tune file the motor runs very lean.

Stats
2003 8.1L
2004 Harness and computer. Stripped out a/c, egr, rear o2 and some other junk. No knock sensors as they will not physically fit with the headers required to jam this motor in a CJ7 tub.
4L80E
Raylar cam (basically a torque cam, nothing crazy)
Raylar springs and retainers
Trickflow full roller rockers and push rods
Intake is stock
TB is stock (new)
Injectors are stock (new)
MAF is stock (new)

egr airflow table has been zero'd
egr filter coefficeint zero'd
egr & air pump disabled
spark, high oct copied to low oct

Tuning with HP in RTT, (2) LC1's. open loop, trims reset

When tuning I raised the VE idle values as high as 150 and finally settled back to about 128 to get the AFR close to the 14 range. Motor still surges significantly.

Copied the RTT values back to editor and smoothed the area. Reflashed pcm and logged the attached file.

What else is going on to require the VE values to be this high?

Thanks and Merry Christmas!

 

did you check fuel pressure

 

That would be my bet too. There's the possibility of getting
>100% VE in some narrow range through resonant action
but high VE across the board says something else is false.

A cam with high overlap can fool a wideband at low RPM,
but you say it's not too crazy. Still I would not worry too
much about hitting a number near idle; go instead for
minimum MAP reading, that is the motor's "happy place".
Record the indicated WB AFR there, and your average
NB O2 sensor voltage average, so you can fix the switch
thresholds later for closed loop and get it to go to the
same place.

 

I have not checked fuel pressure. It's a new walbro pump and fuel cell so I assumed it would be okay. I will have to come up with a pressure kit or some adapter fittings.

Thanks for the suggestion.

 

What fuel rail does your motor have, does it run a vacuum line or not to the regulator if running the 2003 regulator?

most likely the 2004 is static rail pressure of 58# and the 2003 may be vacuum regulated with a front mount regulator. I know the 2003 trucks had a front mount regulator, but I am unsure if they connect to the vacuum or just open to atmosphere like the corvette.

Looking at the stok files, the 2003 vin has the full IFR values at 3.773 g/sec where the 2004 is 3.41 @ 80 kpa and 3.08 @ 0 kpa, so your IFR values are likely incorrect

Ryan

Ryan

 

I posted up incorrectly. The harness is 2004, the computer is flashed with a 2003 program.

The fuel rails use a pressure regulator connected to vacuum. It was replaced before startup, the old one was varnished up.

Looking at my tables,
Engine>General>Fuel Control>Injector Control> Flow Rate vs. KPA
Table is the same from left to right, 29.95. I assume this is lb/ hr. Converts to 3.77 g / sec. Matches up with what you are finding.

 

Hooked a fuel pressure gage on the fuel rail and checked a few things this morning.

At intial prime, gage shows 50 psi
Running motor in closed loop gage stays steady at 49 psi, does not dip much below 48 psi on throttle application.

When I put the motor in open loop, fuel pressure starts dropping, steadily falls until the motor stumbles and nearly cuts off. When I throw it back into closed loop it immediately jumps back up to idle and fuel pressure returns.

Attached is the new log file, but it would not let the updated cfg file upload.


Also in the additional info, I found the cam data for what it is worth.
1.7 ratio rockers
224/237 .510/.545 116.1 LSA / 1.9 overlap

 

More information,

- Walbro GSL392 fuel pump, 11.5v ignition on / 13.84v idling
- I added 5 gal of gas to the fuel cell to eliminate any possible idiot factor from the variables
- Still making 50 psi on the fuel rail as before
- I moved the pressure gage to the pump. If I force the pump on using VCM controls with motor off, the pump makes 60 psi. Turn pump off it drops back to 52 psi and slowly bleeds down (5 – 10 minutes)

What range of static head pressure should this pump be producing?

From what I have found 58 psi is the correct rail pressure on LS motors. Any reason it should be any different on this L18(8.1L)?