97 Sierra miss

[rua2j33]

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!!!

[maxwedge]

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.

[rua2j33]

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!!

[maxwedge]

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