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Q: Need help with code p0303. on 2001 Chevrolet S10

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The first code I had was random misfire. After changing the ignition coil, spark plugs and wires, that code went away, but I now have code p0303 with the same symptoms. The truck shakes at idle, and the check engine light flashes when the accelerator is pressed.
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Since # 3 is the hardest plug to replace you may have cracked the porcelain insulator, best check it to see! Center cylinder on drivers side, the one behind the steering shaft. If you changed them then you know which one it is. Go ahead and replace the dist. cap and rotor too.
I checked the plug today everything looked good. But there was a lot of carbon build up on it and its only been a month at the most with little driving since its running bad. I changed the dist cap rotor when I got that random misfire code
For what ever reason, you still have a misfire on cylinder number 3!!! Spark, gas & compression, you know the drill.
The V-6 and V-8 motors in the late 90's and early 2K's had injector issues. There is an updated injector "spider" assembly for them. Rec. you look into that, and also, (not that this would give you a single cylinder missfire) remove the EGR valve and see if there is a chunk of carbon holding it open. EGR sticking open was a big problem on those 4.3L engines.
have a bore scope of the inside of the cylinder.i found out after i had a misfire and the engine blew up that the number 1 cylinder piston was completely gone and had to replace the engine
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