Hey guys
My gf has a 1999 OBS Tahoe with a 5.7L. One morning it started running rough sputtering and misfiring so I told her to park it until I have a chance to look at it. I checked fuel pressure and it is good. No vacuum leaks. Last tune up was around 40K miles ago when I did plugs, wires, cap and rotor. The plugs still look fine.

It starts to sputter and misfire with load on the engine. I scanned it with my hptuners but the only code I get is P0300 for random misfire. o2 sensors seem to be switching like normal.

Any suggestions on what else I can check? I don't want to throw random parts at it and she doesn't have the money to take it in anywhere.

These are the misfire counts on each cylinder
#1: 12
#2: 492
#3: 0
#4: 2
#5: 1
#6: 1
#7: 0
#8: 130

Bank 2 short term fuel trims go up +15% under load so it is going lean.

 

have you removed the #2 spark plug yet? do a power balance test to better pin point the cylinder on bank 2.

 

The spark plugs all look fine. What is a power balance test?

 

hook your fuel gauge up and do a injector balance test with your scan tool. you'll measure the fuel pressure drop of each injector to see if one is not firing. they should all drop around the same amount. this model has an issue with sticking poppet vavles on the injector assymbly.

 

Hey guys still trying to fix the issue. I just replaced the injectors to the mpfi upgrade and still same cylinder 2 and 8 misfire. If the distributor is bad would it cause all the cylinders to misfire or just a couple? The cap and rotor seem fine. They were corroded a little but i cleaned them up and there was not much difference.

I swapped the plugs and wires around to rule them out but the misfire stays at cylinder 2 and 8.

Any other ideas?

 

You say no vacuum leaks , but these vortec 5.7s suffer from bad intake gaskets also ,have you replaced them ?

That's strange to have 2-8 misfiring like that .

 

Yes the intake gaskets were replaced not long ago.