85GPLEf41

iTrader: (4)

Well my "supposed" 78k mile 1999 ls1 has started to act up a while back.... runs good for about 20-30 minutes before it starts to buck and misfire and backfire!... once it's up to operating temp. Pulled codes with no help until I took it back to my tuner to turn on the code reporting portion of my ECM got code for CSP, I replaced the CSP and the wiring looks good.... Pulled my cats and they were completely hollow! fuel trims won't record? had a code for maf sensor which they tuned out. it's staying in open loop and my b1 s1 has low mv vs b2s1 o2 sensor...he suggested doing a compression test and here are my results I did a "cold" compression test today....
cylinder:
1. 140
2. 135
3. 134
4. 129
5. 145
6. 140
7. 145
8. 135

would a "hot" compression test and or a leakdown test help? or do you think a bad coil would be my problem??

svede1212

iTrader: (3)

Fuel trims won't record? What kind of software is he using? Your compression test is low but that could be cam or gauge and they are close enough together that I wouldn't think that was it if your car runs fine cold. Your best bet is to find a better tuner who can log the car when your issue happens or pick up HP Tuners and do it yourself. Turning off MAF codes sounds like your tuner guy is suspect.

LLLosingit

iTrader: (4)

If it runs good for 20-30 minutes then has problems it's not likely to be low compression related but I will ask.... Did you have throttle blade wide open during your compression test? Having blades in idle position will cause inaccurate readings.
Sorry for sounding dumb but what is a CSP ? It does sound like an electronic issue, Many electronic components take time to get hot enough to show signs of failure.
Popping and backfiring doesn't sound like a coil (Bad coil = dead cylinder)
Cam sensor maybe.

Finlay Macpherson

hi there

i recently had mine comp tested (cold) 80K 2004 LS1

1.180 psi
2.190
3.180
4.180
5.185
6.180
7.180
8.180

for comparison

hopw this of use

cheers

Finlay

85GPLEf41

iTrader: (4)

yeah the fuel trims both long and term are at not "setting" according to my tuner who uses HP tuners and my Snap on solus pro scanner. He took a log and said that the engine wasn't moving enough airflow and suggested maybe the cats were clogged. Code I pulled was P0103 which he said was because he tuned it out and it was in speed density tune. I did look at the engine info pids on my scanner and the cam hi to low was switching so I thought the sensors are ok.I DID get a code for the crankshaft postion sensor aka Cspmy bad guys! replaced the o'reillys crank sensor was replaced under warranty but didn't change a thing even after I did a crank relearn... I did have the throttle body opened with the fuel and coil fuses removed. I did think off the cam sensor but it seems to be working according to the scanner. didn't want to start throwing parts at it. would 02 sensors cause a misfire? read a lot of conflicting info finlay your results are way better then mine......

MODS if need be move to diagnostics!

svede1212

iTrader: (3)

What you really need to do to get help is post up your tune and a log showing when it runs like crap, otherwise we're just guessing.