Lets talk FUEL PRESSURE

[tom joyce]

I pulled the heads off yesterday...exhaust valves are pretty crusty. But between the cost of gaskets,valve job, I "MAY" end up swapping to a 5.7 Vortec...I posted in the 96-up Vortec Performance section.
It was hooked up on a scan tool and the misfires cleaned up off idle, but at idle #6 was BAD. The mechanic said he thinks its a compression issue..possibly valves.

I doubt it is compression issue. A mechanic who "thinks" it's compression issue without testing compression is just wasting your money.
A scan tool that cannot tell you what the camshaft retard setting is NOT a tool that can tell you where the timing is on a vortec.
Exhaust valves get "crusty" when fuel is not being burned (no spark) and running down the exhaust ports AND after about 3000 miles or so.
Your misfire was probably a distributor adjustment away from being solved, but you pulled the heads, so ya mine as well switch out the motor.
350 vortecs are great motors with cheap HP gains...

 

[Manimal]

Ok, so the 5.7 needs to be rebuilt(2 spun rod bearings). So I am having the heads for the 5.0 redone(valve job, spring pressures tested,etc..) I will put the 5.0 back together and use it while I build the 5.7.I too dont believe now it was a compression issue. I am also going to replace the injector spider again since its right there on my bench. Once I have it running, I will take it someplace else for the crank relearn. Tom, maybe youre right , it may have been just an adjustment away from being right.

 

[kenbronnson73]

When you go back together make sure the injector nozzles are in the right holes.A couple are easy to mix up.I didn't think of that before but who knows maybe someone mixed them up before and you just put them where they were when you changed the injector spider .Another thing that happens is one converter gets plugged so airflow through the engine is unequal.This doesn't exactly make sense on your truck because your misfires aren't all on the same bank.But just something to keep in mind.The MAF measures airflow into the whole engine and it gets divided equally by eight and used to calculate fuel.BUT, if the air doesn't flow through both sides equally because of the cat. then one bank get lean and one gets rich and usually the lean one will start missing.Maybe your cat on bank one is restricted enough to cause the lean misses on the odd cylinders and #6 is rich enough to start fouling the plug.Were all the valves the same or was the bank 2 head worse than the other one.You can pull both precat O2's and run it and watch the misfires.If you dont see misfires on your scanner ,you should at least have a generic reader that will show fuel trims.Read the fuel trims ...short term and long term add together to show total fuel correction by bank.If its a cat one bank should be positive and one bank should be negative.Then watch trims with both precat O2's out ,at idle the plugged cat wont affect airflow,and they will go alot closer to each other.If it is a bad cat.Hope it helps you or someone else.good luck

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[Manimal]

OK, she's back together. Runs like a champ in the driveway..havent taken it out yet. BUT it has popped a p1345 code. So I am taking it back to the shop this morning to get the timing set and crank relearn done. I believe that should fix the P1345 code, right? Thank you to everyone that has helped!