Misfire

[kristenc]

I have a 2002 GMC sierra 1500 5.3 and it runs like crap. The check engine light blinks and the codes are PO174B-Fuel trim lean bank 2, PO300B- misfire detected, PO151B-HO25 circut low voltage B251. I just replaced the intake manifold gaskets and it runs the same. I cant go over 70mph and thats with the rpms between 400 and 500. We are having a hard time figuring out the problem Help Please

[longhorn_giant]

Welcome to the site. I'm sorry about the engine problems. Misfire can happen for several reasons. It could be:

 

knock sensors (there are 2, both under the intake manifold. They like to get water buildup in them and crap out over time)

Catalytic converter. Your O2 sensor might need to be replaced, or the whole Cati might be bad

Swollen valves/bushings. I had this problem in my 01 silverado, it was driven really hard before I bought it and the valve stems and gaskets were swollen, causing periodic sticking.

Fuel Filter - maybe it needs to be changed

 

Best of luck, hopefully someone who knows a little more about the codes your engine is throwing can chime in here.

[Operation Mindcrime]

I have a 2002 GMC sierra 1500 5.3 and it runs like crap. The check engine light blinks and the codes are PO174B-Fuel trim lean bank 2, PO300B- misfire detected, PO151B-HO25 circut low voltage B251. I just replaced the intake manifold gaskets and it runs the same. I cant go over 70mph and thats with the rpms between 400 and 500. We are having a hard time figuring out the problem Help Please

Why were the upper plenum gaskets replaced??? Sounds like you have a lean misfire.

Vacuum leak, low or restricted fuel pressure. How's the fuel filter?? Fuel pressure??

Holds when pump shuts off?? Fuel filter plugged??

[kristenc]

I just replaced the fuel pump changed the fuel filter twice put new plugs and wires. Fuel pressure was good with key off. When I did my fuel pump it didnt lock all the way so when I went to fill up gas came poring out from the pump I fixed it but then these other problems started could that have some thing to do with it? I replaced the gaskets cause I was told they might be leaking