4.8 issues got me scratchin my head
04-20-2017, 11:13 AM
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4.8 issues got me scratchin my head Here's the specs: 2000 4.8l with a 0411 ecm
LS1 intake and rail, 24lb injectors (no choice due to clearance issues)
CAI, LS1 TB
External Walbro 255 on 6an line, Corvette filter,
Longtubes, no cats, rear o2's deleted
3" exhaust all the way out
4l60E stock stall
Cam is unknown but pretty sure it's a small aftermarket. Sounds much different than my stock lq4 with headers. Definitely has a little lope to it. Idles at 6-700 rpms
EFI Live tuning.
Swapped ECM with a known good (from my 06 Silverado) to rule out a bad ECM.
I adjusted the IFR's to reflect the change from the 19lb to the 24lb and turned all the abuse management off. Timing and fuel maps are 99F body
Here's my problem: If I give it anything past 30% throttle it just bogs. As in damn near stalls then slowly takes off in rpm and maxes out around 4k. If I tip in the throttle it still bogs but not as bad and will only run to just under 5k.
I've checked the limiter parameters and they are set to hit at 6200 both in gear and in park. Smells absolutely pig rich no matter the rpm BUT my STFT trims are in the +6-7 range and LTFT are +2. I don't have a wideband so I'm kinda sunk there.
I've got no codes pending or set either.
Checked for vacuum leaks and nothing. New mufflers and no cats rules out exhaust restriction. No change if I drop the exhaust at the longtubes.
I'd be extremely appreciative for a direction to look. I'm definitely at a loss here.
LS1 intake and rail, 24lb injectors (no choice due to clearance issues)
CAI, LS1 TB
External Walbro 255 on 6an line, Corvette filter,
Longtubes, no cats, rear o2's deleted
3" exhaust all the way out
4l60E stock stall
Cam is unknown but pretty sure it's a small aftermarket. Sounds much different than my stock lq4 with headers. Definitely has a little lope to it. Idles at 6-700 rpms
EFI Live tuning.
Swapped ECM with a known good (from my 06 Silverado) to rule out a bad ECM.
I adjusted the IFR's to reflect the change from the 19lb to the 24lb and turned all the abuse management off. Timing and fuel maps are 99F body
Here's my problem: If I give it anything past 30% throttle it just bogs. As in damn near stalls then slowly takes off in rpm and maxes out around 4k. If I tip in the throttle it still bogs but not as bad and will only run to just under 5k.
I've checked the limiter parameters and they are set to hit at 6200 both in gear and in park. Smells absolutely pig rich no matter the rpm BUT my STFT trims are in the +6-7 range and LTFT are +2. I don't have a wideband so I'm kinda sunk there.
I've got no codes pending or set either.
Checked for vacuum leaks and nothing. New mufflers and no cats rules out exhaust restriction. No change if I drop the exhaust at the longtubes.
I'd be extremely appreciative for a direction to look. I'm definitely at a loss here.
Last edited by kawijames; 04-20-2017 at 11:17 AM. Reason: Add info
