03 S10 Misfire/Shaking

I recently purchased a 2003 S10 2wd 4.3 Vortec Automatic with 122,000 miles on it.

It was running and driving fine but now it seems to misfire when warm.

So what is happening is when the truck is started up and driven it goes fine, but then after about a mile of driving or a few minutes of just running in park it starts to get a little shaky and when revving it above 1200rpms it starts to feel like it is misfiring.

I replaced the spark plugs with AcDelco, I replace the spark plug wires. I replaced the fuel filter. I will say after the spark plugs and wires replaced it does feel like it runs stronger.

I am just confused on what is wrong, the fuel pump is a little loud but supposedly this is normal on these things.

It does not have a flashing check engine light when this misfire/shaking is happening and when you get down on it, it seems to go ok.

I had someone suggest it is the coil, another says the cap n rotor but the cap n rotor on it is not original it looks to be one of those cheap valuecraft ones and to me a cap n rotor would not make sense if it is running fine at first but starts acting up when warm.

Any ideas? this engine sounds beautiful overall it is just this one issue.

• This topic was modified 3 years, 9 months ago by Brandon Towne.