2000 K1500 P0300

[HV_handyman]

I have a Chevy 2000, with just over 100,000 miles, a K1500, that misses when the load on the engine is removed at highway speeds (65-85MPH). I have changed plugs, rotor, wires, had it to two Chevy dealers. No help after 8 hours and a $400 bill. Runs fine at idle and is worst when cold. When the RPM is at about 2500 to 3000 is when it's the worst. Easiest way to set the code is drive with the cruise on and go down a hill. (I have thought about driving I over the hill, but can't afford a new one). Any help would be appreciated.

 

Thanks,

[pbutler6]

YOU MIGHT WANT TO CHECK YOUR CAT FOR TOO MUCH BACK PRESSURE

THAT WILL MAKE AN ENGINE MISSFIRE AT HIGHER RPMS.

[5.3isnota327]

If you changed the rotor, I am going to assume that the truck is an old body style 2000 with the 5.7 vortec?

 

If it is, look at the fuel system...filter, pump pressure, regulator.

[HV_handyman]

If you changed the rotor, I am going to assume that the truck is an old body style 2000 with the 5.7 vortec?

 

If it is, look at the fuel system...filter, pump pressure, regulator.

 

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It is a Vortex, but is a 4.3 V-6. I am wondering if it's a vacuum leak. I plan on changing the PCV valve and looking at all the vacuum hoses for splits or holes.

 

It's a strange thing for sure. When it's cold, trying to run the engine between 2200 & 2800 RPM it just misses terrible. After it warms up, it runs better, but cruising on the highway with the cruise control set and going down an incline (no load on motor) is a sure way to set the P0300 code. Thanks for your replay,

 

Leroy

[HV_handyman]

YOU MIGHT WANT TO CHECK YOUR CAT FOR TOO MUCH BACK PRESSURE

THAT WILL MAKE AN ENGINE MISSFIRE AT HIGHER RPMS.

 

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.How would I do that? Never had the pressure checked, but I did replace the post cat Oxygen sensor. It was really bad. Looked like some one hit it with a hammer. After that replacement, I got one time an error code of poor efficiency on the catalyst.

[95Sierra2500]

Could be several things, but you've mentioned the regular tune-up stuff. My next place to look, if I were you, would be the cat. It could be going bad, which would cause misfires. They're only $80 at Autozone. If your cat checks out fine, I would suggest checking your fuel pressure. My fiancee`'s 99 Jimmy's fuel pump was dying and was causing it to misfire. It got so bad, in fact, that it wouldn't start even though the pump would prime. Changed the pump, all has been well for almost 6 months!

[Xcopterdoc]

I've run into a few of these. Tuff to diagnose. A couple were bad caps, one had a worn out dizzy and several had intake leaks on the upper side. Its a random misfire. Have it scanned and have them look at each cylinder.