New engine, popping under boost??

[farmtruc]

Hey guys,
Just got my customers engine installed in the ol truck and I'm having an issue with it.
I haven't done too much troubleshooting, so feel free to suggest anything.

The truck runs great under normal and non boost conditions. As soon as it hits a few psi 2-3, the truck will start to backfire or pop out the exhaust.

Now when I first got this engine together, for some reason the #5 piston blew a head gasket. I immediately replaced it and now it's back in action.

I gapped the plugs at .025, probably closer to .023 so the 9.5cr doesn't blow the spark out.

Like I said I haven't done anything else, but I figured I'd post up and go through the troubleshooting stages and share.

I guess tomorrow, the process is:

Check plugs for consitency
Compression check - engine can't be hurt, too soon and not any hard runs on it.
Make sure gasket didn't blow again
Change out coils
New plugs

The tune is good enough to not cause anything , so I'm counting that out.

any suggestions?

thanks,
allen

[Sleaper]

Hey guys,
Just got my customers engine installed in the ol truck and I'm having an issue with it.
I haven't done too much troubleshooting, so feel free to suggest anything.

The truck runs great under normal and non boost conditions. As soon as it hits a few psi 2-3, the truck will start to backfire or pop out the exhaust.

Now when I first got this engine together, for some reason the #5 piston blew a head gasket. I immediately replaced it and now it's back in action.

I gapped the plugs at .025, probably closer to .023 so the 9.5cr doesn't blow the spark out.

Like I said I haven't done anything else, but I figured I'd post up and go through the troubleshooting stages and share.

I guess tomorrow, the process is:

Check plugs for consitency
Compression check - engine can't be hurt, too soon and not any hard runs on it.
Make sure gasket didn't blow again
Change out coils
New plugs

The tune is good enough to not cause anything , so I'm counting that out.

any suggestions?

thanks,
allen

I would say it sounds like plugs, wires or coils. Is there any wires that have been nicked or boots that aren't seated all the way? Are you using the stock coils?

[farmtruc]

...stock coils?

using stock coils, but i'm going to try a set of msd's tomorrow.

[GasGuzzler]

Valve float, broken valve spring, poor sealing valve seat, cam advanced or retarded, low fuel pressure, faulty MAF (if MAF tune), CKP failure, loose reluctor, incorrect reluctor....

[TurboMic]

i say some plug wires burned on the turbo manifold.....like mine did on us.....lol

[dropem]

i have the exact same problem but mine goes completly away when my motor warms up so keep us posted

[RedHeartbeat]

Bad valve springs? Weak? Wastegates popping early?

[farmtruc]

Valve float, broken valve spring, poor sealing valve seat, cam advanced or retarded, low fuel pressure, faulty MAF (if MAF tune), CKP failure, loose reluctor, incorrect reluctor....

valve float at 4krpms and 3psi with good springs, probably not, but i'll check the springs, a bad spring could cause valve float.
could be poor sealing valve, i'll check that.
cam in straight up, runs too good under no boost conditions.
fuel pressure, rock solid! a1000, -10 line everywhere, aero fpr.
no maf
i hope it's not ckp or wheel, that would suck!
i don't think it's the wrong wheel, it would backfire and spit randomly and a lot more often.

i say some plug wires burned on the turbo manifold.....like mine did on us.....lol

changing those tomorrow.

[GasGuzzler]

i have the exact same problem but mine goes completly away when my motor warms up so keep us posted

Classic lean or low volume fuel problem.

[farmtruc]

i have the exact same problem but mine goes completly away when my motor warms up so keep us posted

When the engine is cold, open loop, the pcm is using the ve table. If the ve table isn't rich enough, your engine could be experiencing a slight lean condition. When it gets warm, the the maf takes over and patches everything. The ltrims are probably positive, and the pcm adds fuel, which corrects the lean pop.
Or, the fuel pump isn't good enough.