car will sit and ilde fine all day long once you put it under load it backfires by backfire I a loud pop out the exhaust . Its very random it might do it once in a minute or 5 times . Just about everything on the car is new . Everthing listed is new : Opti,ICM,coil,plugs,wires,fuel filter, . The fuel pressure stays around 35 may go up to 38 or 39 but falls no less than 35 psi. I was gonna change the fuel pump but not sure if its the problem . Not showing service engine light or any codes on the scanmaster. Im not sure what to do ive triple checked everthing . Someone told me could be a stuck valve and to double check the valves. Everyones imput is greatly apreciated
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is it missing?

pretty sure fuel pressure should be 43.5 psi, no more no less and dropping that low could be an issue, or an inaccurate gauge

your issue sounds like a spark miss though, do you have any codes? not just a light you need to actually scan it

what brand opti did you use?

what plugs did you use and what were they gapped to?

and wire type?

 

its a gm opti . they are ngk plugs gapped at 40 or 43 i think . I have a lt1 scanmaster and it isnt showing any codes . looks like it has good spark . as far as fuel pressure ,I was told being off by 8 psi shouldnt have much of an effect but that what I was leaning toward myself . The car seems to have good power .

 

It idle, with vacuum compensation line off the fuel pressure regulator, should be 43.5psi, with anything in the range of 41-47psi meeting GM spec. Attach the vacuum line, and it should drop about 5psi below the "no vacuum" reading.

It should hold at least 40psi under full RPM/load. Running at 35psi would reduce fuel flow by about 10%.

If its misfiring, the air and fuel will end up in the exhaust, and it may light off and pop.

 

Sorry for the double post . So it may be worth it to change the pump ? I will try what u said to do and see where its at . I appreciate your response

 

i checked fuel pressure with vaccuum off it was at 39 psi and as soon as its hooked back up its 35

 

Was the vacuum line dry - no fuel in it?

 

no fuel lots of vaccuum though

 

any other ideas. or would changing the fuel pump be the best bet

 

try disconecting the maf and see how it runs, just a shot in the dark here

 

I think I may have found my problem . I have 2 lifter that are bad I can push on the pushrod and push the lifter right in . I have the Hotcam its possible they are still the stock lifters right . Ive been doing some reading and people are using LS7 lifters should I use them or what would be reccommended and where can I get them

 

the ls7 lifters are not the standard replacement for an lt1, so yes - use them

you can get them pretty much anywhere, look around to find the best price