Pma93

im having issues with my LS1.. its got a mild cam upgrade, exhaust system and a mafless tune and has a t350 race gearbox.

awhile ago i would just be driving along and when i backed my foot off accelerator (to brake/slow down) it would on occasion cut out - as if te key had cycled off, and usually would start up and run fine straight away.

this got worse and when the engine was cold it would try to cut out under normal driving conditions, but would kind of save it self from completely stalling - so it would cut out but quickly cut back in if that makes sence. it did this a couple of time until the engine warmed up (not sure if temp actually is related to fault)

for awhile if i idled it for 5-10 mins each morning before work i wouldnt experience any fault. however after some period of time it has now begun to cut out when idling. It might last maybe 2 minutes then will just cut out.
it will start again first shot and run fine, it will the cut out once again but after a few shots the engine starts but runs noticeably worse (rpm drops off, sounds like its missing though might just be low revs)

ive been trying to get my head around this issue for a few months now and cant seem to come up with anything.

i was hoping the may be someone on this site that could of experienced similar symptoms or would be able to lead me in the right direction.
thankyou.

NightwalkerLS1

iTrader: (2)

Sounds like you might have a dirty iac valve. I had the exact same issue. Cleaned that bad boy and issue gone.

BigEd_72455

iTrader: (7)

You sure the fuel filter is on the right way? Some of them are reversible for connection, but are backwards for efficient flow.

It sounds to me like your relay for the fuel pump is dying on you, or the pump itself.

Try replacing the fuel pump relay with a BRAND NEW one, don't just swap them around. If that does not help the problem, then get a fuel pressure gauge and attach it to the rail, start the car with the hood up and watch the pressure gauge when it tries to die or cut out on you. IF your pressure has dropped down below 25 to 30 or so, then you have something in the fuel system causing a problem.

If you are going to go through and pull the filter off again, disconnect the line at the rail and hit it with an air gun, short quick burst and make sure you have something to catch what comes out also. if it blows through clear, then re-attach it. you might have something clogging up the fuel lines or even the rail.

Diagnose the fuel system, and if that doesn't seem to help it any, then look at other parts of the system.

Pma93

thanks guys will deffinatley be looking into those in the next few days..

not sure if was worth pointing out, sometimes when i just hit the accelerator and give it a quick sharp rev, when i let my foot off it sometimes cuts out also..

not sure if that will lead us down a clearer path or not but thought might be worth a mention.

BigEd_72455

iTrader: (7)

That points to your regulator getting stuck...

get a pressure gauge on the rail and check your pressure, then play with the throttle some in the driveway. My 5.3LS has 48 PSI at idle and running steady, but jumps to 56-58 on acceleration. Yours may be the same, or it may be at 58 at idle, and jumps higher on acceleration.

Somewhere in here is an old thread about regulators and pressures...

Napa should have them on the shelf, or be able to get them overnight. I know mine was able to.

Pma93

hooked up a scanner, had a code for evap purge solenoid..

run engine with harness plugged in and unplugged, revved engine and it wanted to, or did, stall/cutout.
removed evap purge solenoid and revved up engine ran fine and didn't even sound like it wanted to stall.

is it possible it was stuck when engine ws cold, but once had warmed up it un-stuck ?

BigEd_72455

iTrader: (7)

Probably more along cold was flooding and warm it could burn it off faster.

Replace it or remove it. I don't have one. If its the valve at the top of intake right behind throttle body.