I had a long overview in boosted section but it’s more appropriate here. I am 78 but learning hp tuner. My procharger ls3 started surging out of the blue. I put in new plugs that helped but none looked bad. I scanned it and the ltft go higher with rpm. The injectors were sent in and three were leaking. I thought that was it. Same light surging +18 ltft is the same. My maf was cleaned but it seems low compared to my Silverado 5.3. I took the battery cable of and scanned the next day. Same trims. I see idle maf and 2500 rpm maf about half what my truck shows. This car ran perfect then I took it off cruise and this began. I had old gas in it but that doesnt seem to fit the issue. Anyway, new maf coming.

 

It would be helpful to see a HPTuners log

 

It appeared like the MAF was under reporting so I switched in another one. No change. I smoked it to no avail. Since it happened so suddenly it's puzzling. Now I'm thinking vacuum leak but am anxious for an experienced opinion.

 

By the way it's procharged to 13.5lb Alky Injection with boostapump and a lumpy cam.

 

no cats no rear sensors

 

I posted it if you can read it with hp tuner. Very frustrating, Smoke found nothing and trims improve with engine speed. Strange that it goes max timing as soon as I raise rpm.

 

How's the gas? Is it with the same tank? Exhaust leak from headers before it hits the primary O2s? Are you logging/have eyes on the AFR with a wideband?

I've had surging issues with a bad exhaust leak that would end up pegging the LTFTs at idle/low RPM. Seemed to even out into higher RPMS but since the car will keep the + fuel to be safe, it'd run like poop up top. Not boosted though.

 

I ran the old gas until the low fuel light came on. Then filled it up. That’s about half gone. Not using wideband. Only the scanner. Another gentleman is helping with tuning advice and things to check. I have to think it’s not tune related since it was sudden and remains the same after new plugs and wires, different maf and map, smoke test, new intake gaskets, cleaned and flowed injectors. I have no header leaks but did see some signs of leaks near the O2’s where the mid pipes clamp on. This act like a carburetor with a lean transition circuit or arcing plug wires. Around 2000 rpm it’s stuttering and the rpm dances a few hundred both directions. At speed it’s just surging/hesitating like too much timing or vacuum leak. Even though fuel trims get richer with rpm they still are all over the place. It also will die if I back down in gear off throttle. The vacuum goes 20+ and just before stopping I can pop the clutch or starter and it’s running. I also pumped fuel in a bucket with it running using my pressure gauge release. It pumped a quart in 30 seconds. So I don’t think volume is a factor. The tuner guy noticed a crazy spiking on bank 1 sensor. I’m swapping coil pack side to side and sensors switch after that to see if the spikes follow. The plugs that I changed had no indication of damage or fouling. But, the new plugs did make the hard surging better. That was odd to me. Still no codes or misfiring on scanner. I’m about done with computer cars.