steven4177

Have a 2006 gmc cutaway with a 6.0l that was given to me about a week ago. The van wouldn’t start. Checked codes and had a p0300. After checking the basic found someone put auto lite plugs in and most was not sparking. Replaced with a/c delco plugs and van would start and die. If I played with the throttle it would stay running and after a few seconds I could release pedal and it would idle on its on. If I tried to give it gas it would bog down and start backfiring. Checked fuel pressure and had 56psi and would leak down when ignition turned off. Started engine and pressed the bleeder valve on the fuel pressure gauge and van would die. Bought new fuel pump and van now has 60 psi fuel pressure at idle. And can now press the button on the gauge for volume and van stays running. But if I press the pedal down the van acts like it’s about to die and pops/backfires and then will catch it self and rev high. I can very slightly and easily press the gas pedal and it will do fine and will rev up. It is only if I press it quick and hold or press it quick and release. I can press and hold and it will catch it self after a second and rev up. If I slowly get rpms to 750 or higher then floor it then it revs great. But at a idle of 550 it doesn’t do well will a sudden press of the pedal of and great amount. Hopefully someone will understand what I’m saying the issue is. Not great at explaining stuff. Maybe I can get a video of it and post on here if someone wants. Engine sounds good idling and sounds good when it revs up after it catches up. No codes currently present. Any help would be appreciated as to why the van is doing this. Any ideas as to what to look at next?

Triaged

What are your fuel trims at? MAP MAF? Does it work better if you unplug the MAF?

steven4177

Can get the fuel trims in a couple hours when I get back to the van. Will also get the map reading at idle and when giving throttle same with maf reading. As far as unplugging the maf doesn’t change anything

steven4177

Ok here we go
Key on engine off
map 30
ect 45
iat 54
maf 0.00lb/min

engine running
rpm 550-580
fuel 62psi
ect 181
map 10
stft b1 -3 to 0
stft b2 -5.5 to .08
maf .80lb/min

engine running
rpm 2000
map 8
tps 9.8%
maf 2.5lb/min
stft b1 -2 to 4
stft b2 -3 to 6

did give me a little trouble starting it up and getting it to want to idle just now. Wasn’t running like it had been the last couple days. More popping today then usually. As noticed when trying to hold rpm steady at higher rpm it would drop down a good amount then would come up a little higher then back down. Eventually it stayed right at 2000rpm

steven4177

Ok now it’s back to running like it had been for the past couple days

steven4177

Idle at operating temperature
Stft b1 -2.3 to 0
stft b2 3.9 to 11.7 why is it adding so much
map 9
rpm 544-561
iat 66
Maf .06 lb/min
02 b1s1 .7-.9v
0s b2s1 .015-.860
tps 0%

Triaged

What's the long term fuel trim? Short might be so high because it is canceling our the long term now that the misfire is fixed.

steven4177

Ltft b1 20.3
ltft b2 25

Triaged

MAF at idle seems about right so you might not have a vacuum leak.

Triaged

That's a lot of fuel trim.