1999 Chevy 1500 4.3

Asked by Dec 17, 2015 at 08:49 AM about the 1999 Chevrolet Silverado 1500

Question type: Maintenance & Repair

I have a 1999 Chevy 1500 with a 4.3 I'm having a
really uncommon issue with. I'm a mechanic and
I've asked several and no one knows what the
issue is. The truck does this thing where after
driving for so long ( seems to be after about 20-30
minutes of driving) if you go to lay into it say
getting on the highway or passing another car it
starts to spit and sputter and won't gain speed
when floored, but it just slowly gets worse the
farther you drive. It gets to the point you can only
go to about 2000 rpms other wise it will not gain
speed it just spits and sputters. If you shut the
truck off and let it cool down it does fine but then
after a while of driving the issue comes back. I put
it on a scanner and it was only throwing all O2
sensors. They were both replaced and same issue
still the cats were replace before I bought the
truck. I honestly I have no clue what the issue is.
Has anyone had this issue?

3 Answers


Try testing the fuel pressure, and do a thorough check for any vacuum or exhaust leaks.

Well I was told that year they had an issue with fuel pump which I replaced back in September and I didn't start having this issue until the end of November and I've checked vacuums and everything I'm stumped on this truck


Have u checked to see how much voltage is coming out of the Alternator. Since everything is based on electrical relays and solenoids, I would check that. My friend had a problem similar and it was over charging and was screwing everything up. A place to start. It could be the computer. If you have a local auto salvage yard see if you can find a working computer. I am a retired mechanic and I having to learn all this crap by trial and error, which can be expensive. I have a 2003 Silverado extend cab 4x4 LT and it only has 113,000 miles on it and runs great so far. I did have to replace the Dash Cluster. But I now have a problem with my right rear brake light not working. It has a towing package and was told to trace from there. So I got on this site for one to help people that have similar problems I have had in which I fixed, but also needing to learn what future problems I might run into what answers come up. Good luck, and if you do get it figured out please post the fix. And it isn't just Chevy that have these problems so do other makes. But us Chevy truck owners need to stick together and help figure out the problems that come up.

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