Help with 2000 5.3 misfire.

[trapperman83]

Truck was running rough and cut out at high rpm checked fuel pressure and was up to 53psi checked regulator it was good, so then I got a misfire code for #4 cylinder and a multi cyl misfire, so I replaced the #4 coil and drove it and it made a big improvement but still not perfect so I got a new plug and then things ran a lot smoother at high rpm, but it still seems to be holding back at higher rpms, I just replaced these plugs 2 months ago, I'm wander if maybe all of the plugs are messed up now or I have another bad coil, all new plug wires as well, I used auto lite iridiums for the plugs, should I replace the rest of them.

[desrtrat]

replace all the plugs with AC Delco..they seem to work the best with LS based motors..

[trapperman83]

Do u think it toasted them

[oldscsc]

Fuel pressure spec is 55-62 PSI key on / engine off. 2 PSI is enough to make a difference on these engines.

 

You would notice the issue manifesting itself as a low power concern at higher RPMs as the fuel trims lean out.

[trapperman83]

Yea i tried it with the key on and it was much higher lol. i had it running before. i just put a brand new acdelco pump in it because i had a bad fuel psi tester it said it only had 40psi so i changed the pump for nothing and the Delphi pump that i put in there was only a year old.

I went and got all new acdelco plugs so hope that fixes it.

[txab]

What gap are your plugs? GM issued new specs since 2000. .040 is the recommended gap not .060 that was the previously the norm.

 

AC # 41-110

[trapperman83]

Got new ones gapped at 40. I ripped one of my new premium napa wires, ugggg, wander if napa will give me a new one without the receipt.

[trapperman83]

Well the ac delco plugs made it run better for sure. Gonna roll with it for now, any more problems then I'm gonna look into the intake gasket.

[desrtrat]

Well the ac delco plugs made it run better for sure. Gonna roll with it for now, any more problems then I'm gonna look into the intake gasket.

glad it's running better. you can also try 2 cans of seafoam.2/3 thru the intake, and the rest in the tank..can't hurt for under $20.