Chevy gurus vortec 350

[Cperry]

99 suburban 350 vortec has a #5 misfire. when i got it had new plugs, cap, wires and rotor replaced.

1. getting good spark to plug
2. Plug was wet when a pulled and was white as in no fire was happening in the cylinder.
3. Unburned fuel is exiting the exuast
4. No intake leaks from what i can tell, sprayed carb cleaner and listened.
5. ECM is sending a ground to injector, power source to injector is good.
6. Injector is releasing fuel pressure when jumped.
7. compression is at 175 psi, did a cylinder leak down test varified intake and exhuast valves are opening, also pulled valve cover and insured rockers were moving.
8. checked harness grounds good.

so basically i got fuel, fire, air, and compression but the biatch aint firing.

 

[Rich]

Hmmm, good one..

When you say "good spark"...

Might pull an adjacent plug and compare the 2 sparks.. maybe that one is weak enough that it's snuffed out under the pressure of combustion?

swap one wire for another?

is that terminal in the dizzy cap OK?

I think it's a weak spark, in case it wasn't obvious...

 

[Cperry]

ya i tried swapping the wires and pulled all the wires on that side for spark......

anyways figured it out, pulled the intake and it had an internal intake leak. sucking enough air to keep it from firing, thats my theory anyway awaiting the gaskets to go back on. i will let you know if this fixes it but i am pretty sure thats what it is.

 

[Rich]

Ahhh, they are famous for intake leaks from what I've heard.. so it was leaking from somewhere the carb cleaner couldn't reach?

 

[Blkvoodoo]

yup, 350 Vortec is notorious for intake leaks, internal and external, have even seen a few of the intakes CRACKED in lower intake runners ( yes the aluminum cracked) BE certain you follow the torque spec clean the threads and BLUE locktight the intake bolts, it'll make a differance.

The gaskets are shit, pure and simple. the newer LS engines aren't much better. Those Phenolic manifolds tend to crack AND/OR warp.

lot 'o' fun !