I hope this is in the right room...

Like it says. My buddy has a 98 Silvy w/ a 5.7 Vortech in it. He had a bad misfire and replaced the cap, rotor and wires. Still doing it. He pulled the #3 plug and it has oil on it. He says it doesn't smoke on startup, nor while running.

It doesn't misfire until it is fully warmed up. He says it's not as bad when it's around 160*. The truck sat for three years, w/ little attention. I told him to check the compression since he suspected a broken piston ring.

Injector? The only code it stored is Misfired Cyl 3. PO303 I believe.

It has the central injector design, BTW. This truck is running like S**T! It sputtering like MAD.

Thanx all...

 

That injection system has been known to fail pretty often and cause all sorts of sputtering and misfires.

 

P0303 is just the code for a misfire in cylinder 3.......i had the same problem with my truck but just the opposite, when it was cold it would misfire then when it warmed up it ran fine.....turned out to be my intake gasket warping when cold then seating when warmed up.......dont know if that is your problem or not but might check gaskets around # 3 for a vacuum leak of some kind........

 

Sweet.. Thanx for the help guys!

Any way to diagnose the injection system on that truck? It sounds like it can't just be one cyl misfiring. it runs rough as h3ll...

 

^ Bump...

ANy help with trying to diagnose a bad injector(s)?

 

I am wondering the same thing. A buddy of mine has been trying to fix the same issue on his wifes 99 Taho with the 5.7 for over a year. He had A Vertronix scanner hooked up on it today and it said his cam Timing was at 45 degrees. He said that didn't seem like it could be possible though as the idle seemed fine. He is a mechanic by trade. He has done computer swaps to see if it was the Drivers inside going bad but at this time it does not seem to be fixing the issue. I was wondering if there is any way to tell if it is a faulty sensor or something else along that lines??? Has any one else come across this issue???

FWIW His did have minor front end damage apparently at one time but I dont know how extinsive it was. He purchased it used.

 

Im pretty sure that engine has the "SPIDER" style injectors and they always plug up. The new style actually has the injector pushed down into the head. They work much better and add a lil horsepower.

 

I would start with a new set of plugs. You said you had a new cap, roter, and wires. I would also go ahead and check for vacume hoses that are in bad shape (also make sure they are all plugged in) Then go around with a can of carb cleaner (or like substance) and see if you have an intake leak. If all of the checks out then I would go through the injectors.

 

On my buddies 99 5.7 taho, he already put plugs and wires and checked the injector signals and values through the computer. I dont know about a cap and rotor but he would have replaced it if there like the old school type. He said the signal comes from a crank sensor or something like that.

Any way curious about that manifold leak everyone is speaking of.

 

The manafold can suck air in from a tear in the gasket or a leaky vac. line. If unmetered air enters into the engine it will make it run like poo.