Hi all,

I have a 97 Sierra with a 4.3L. The Service Engine Soon light keeps coming on with the p300 code showing up. It has a miss throughout the driving range, but is most noticable at higher speeds. I have replaced all of the following:

Cap
Rotor
Wires
Plugs
Coil
EGR
Cat Convertor
Fuel/Air Filter

Also, the gas gauge is acting up. It will not drop down below 1/2 tank. Could this be related?

Any ideas? Thanks!!!

Welcome to AF. Probably not an issue with the fuel reading. If this is a noticeable misfire, try and isolate the cylinder either using a full function scanner that can do a misfire or power balnce test, or disconnect/short one wire at a time to pinpoint the cylinder for starters.

Thanks for your response Max. I have checked and there is spark at each cylinder. One thing I forgot to mention is that it will chug at high speeds. For example, If I hold the speed steady at 70, it will start to chug or if I am on the gas and let up quickly, it will chug. It doesn't always happen, but it did yesterday and this morning.

Thanks again!!

I"d check your fuel pressure at the rail here, look for 60-65 psi.