Random cylinder misfire!! Help!

[Sublime69]

My 99 silverado 5.3 with 150K has a crazy misfire. When the motor is completely cold (in the morning) it will run fine untill it gets gets warmed up or if i drive it for a while turn it off then turn it back on, it will idle really low and shake really bad, when i acdcelerate it misfires like crazy and has no power unless it is wide open throttle.

Any help would be great! Thanks

[j cAT]

Originally Posted by Sublime69

My 99 silverado 5.3 with 150K has a crazy misfire. When the motor is completely cold (in the morning) it will run fine untill it gets gets warmed up or if i drive it for a while turn it off then turn it back on, it will idle really low and shake really bad, when i acdcelerate it misfires like crazy and has no power unless it is wide open throttle.

Any help would be great! Thanks

this could be egr valve. check for codes/remove egr sticking

[Sublime69]

Originally Posted by j cAT

this could be egr valve. check for codes/remove egr sticking

There is no egr codes that come up.

[j cAT]

Originally Posted by Sublime69

There is no egr codes that come up.

what codes do you have? remove and check egr for debris causing sticking that way this can be eliminated......

[ripptide56]

I had the same problem with my 2001 6.0. It turned out to the the fuel pressure regulator. It runs fine and then when you start it up again it will give the blinking check engine light and run rough and if you try to drive it like that you can only due about 20mph. I hope this helps..You can also search the forums on how to check it,but the part was only $50 bucks so I decided to replace it.

[wafrederick]

A plugged up catalytic converter will do it too and will take out a 5.3.I have seen this happen,one from an used car dealer that is a very good customer.It had no power and misfires after changing the engine,the catayltic convert was plugged right up.Do a back pressure test with a back pressure gauge to confirm this.

[Sublime69]

thanks guys, but it ended up being a bad o2.

[j cAT]

Originally Posted by Sublime69

thanks guys, but it ended up being a bad o2.

that is strange no codes , and miss fire this is not the norm.....plugged cat or egr is what i thought...

[ripptide56]

What o2 sensor was bad? Before or after the cat?

[Sublime69]

My buddy has HP Tuners, its a program that lets you tune any LS based motor. So he hooked it up to my truck and the pass side front o2 was pegged rich so the computer was pulling out 20% fuel. So we switched the o2s and the problem followed to the other side. So i bought a new o2 and it fixed the problem. I have no idea why it didnt throw a code for it.

[Bmullin]

hey man have the exact same problem as you but its my #3 cylinder just wanted some advice what did you do, or what do you recomend?

[Sublime69]

Originally Posted by Bmullin

hey man have the exact same problem as you but its my #3 cylinder just wanted some advice what did you do, or what do you recomend?

your situation is different since you know exactly what cylinder it is. How many miles do you have on it? It could be bad intake gaskets. When i first got my truck it had one cylinder that was misfire and the intake gasket was bad. The gaskets have rubber o-rings around each port and the o-rings were dried out and cracked. you could also try swapping the coil and injector with another one and see if the problem follows.