2000 Silverado hesitation
 

Hello all, Im new to the site and look forward to talking to you guys!
Im having an issue with my 2000 Silverado 1500. Its got the 4.3 V6, only 102,000 miles, and Im pretty good about changing oil, checking fluid levels, and general maintance at the appropriate intervals.
For the last few months, shes been just kinda running a bit rough. Its gotten progressively worse as of now. What Im getting is some pretty bad hesitation at high speeds(50-55mph). I mainly notice it when cruising at 50 and try to accelerate, thats when the bucking bronco comes to life! I did some tune up stuff, and only got a check engine code once. Code P0301 Cylider 1 misfire. So i changed plugs (Bosch), wires, distributor cap and button, checked/cleaned EGR valve, and ran some fuel injector cleaner thru it. About 3 years ago I had the fuel pump and sending unit replaced. I also replaced the fuel filter on the chassis rail. Im running out of ideas here! After the code came up, I changed the distributor cap and button then cleared the codes. It still hesitates at higher speeds but no codes have come up since. Theres virtually no hesitation accellerating from a stop, just only when your at driving speed. Hoppefully, you guys can steer me in the right direction! Thanks in advance!

Don't know much about the 4.3's, but both my wifes 5.7 and my 7.4 had similar problems. The idled fine and putted around town ok, but put any load on them and they started sputtering. Even got cylinder misfire codes on the 7.4. Turned out one of the cats on the 7.4 went bad. and a bad O2 sensor on the 5.7. Can't remember if it was the upstream or downstream sensor thought, sorry.

thanks, Ive read that if the cat's go bad you will smell a "rotten egg" smell coming from the exhaust, but theres nothing like that happening with my truck. Look forward to any more replies!

just a thought... I bought pre-gapped plugs and assumed they were correct and didnt check them. Could it be possible that one of the plugs are not gapped right? Will an incorrectly gapped plug do this?

Yes it will cause a misfire. Being thats is a mis at highway speeds, Im thinkin its gonna be ignition related.

should I start thinking about replacing coils? is there any way to check ignition issues? I dont see any arcing in the dark while the engine is running...Thanks again.

Did it kick up a code at all? The only code my reader showed was Cyl. 1 misfire. If an O2 goes bad, wouldnt there be a code kicked up?

Also, I happened to save the old plugs just in case, and gapped them. 5 gapped about .058 and one gapped .070. Factory calls for .060, so could that one wide gap cause this trouble to begin with? none of the plugs were burnt or in bad shape, just normal visible wear and tear, according to diagram in Haynes manual.

You could check the O2 sensors. Easy way is switch them, the front ones only and see if the misfire code follows.

So is there anything I can do to diagnose ignition problems? Seeing all that I have replaced to date, do i need to go ahead and replace the coil? Im on a pretty fixed budget these days and dont want to replace things that dont need fixin'! Thanks for you guys help thus far, this is a great forum!