4.3l running rough at 65mph - Engine Troubleshooting


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4.3l running rough at 65mph

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roadkill
New User

Jul 16, 2010, 6:29 PM

Post #1 of 4 (1562 views)

4.3l running rough at 65mph	Sign In

I have a 97 K1500 chevy with the 4.3L with 138k on it. My truck seems to stumble around 65 mph in cruse control and it is worse with overdrive off. the only code that comes up is for a random misfire. code only shows up from time to time. The truck idles very smooth and has i plenty of power under load. I have changed my cap and rotor already, had a similar problem once and that fixed it. This time it didn't fix it. then i changed my fuel filter, still no change. I have checked my air cleaner. I changed my plugs when i got the truck 2 years ago and only put 11,000 on it since. I put platinium AC delco's in and installed new plug wires. Today i hooked up a fuel injecter cleaner up to it and used snap on fuel injector cleaner. I did that 3 times today. I took it for a drive, still no change.

Has any one experience this issue or does any one have the answer. I rather not keep slapping parts at it.

Sidom
Veteran / Moderator
Sidom profile image

Jul 17, 2010, 10:00 PM

Post #2 of 4 (1554 views)

Re: 4.3l running rough at 65mph	Sign In

A couple of things come to mind....

If you can, hook up a vacuum gauge an take a reading while it's missing. If the reading is shaky, you may have a valve sticking on it.

You may also have a fuel pump going bad. That's a little tougher to pinpoint without the right tools. If you have a scanner, take a look at the fuel trims, the long term in particular. If it's getting into the double digits close to 20% positive while under load that goes back to singles while at idle, there's a very good chance the pump is going out. Normally you have to get over 20% fuel trims to set lean codes..

If you can pinpoint the cyls misfiring you could do a compression & running compression reading to see if anything comes out of that.

There are a few other tests you could run but those would require a scope..........

roadkill
New User

Jul 18, 2010, 11:44 AM

Post #3 of 4 (1551 views)

Re: 4.3l running rough at 65mph	Sign In

thanks for the help Sidom. I have actually now got the problem fixed. After doing some checking into other forums, I found couple people mentioned about the distributor drive gear wearing out. That made the most sense to me do to it driving fine under load and it idles good and only 1 code being logged multiple times(random cylinder misfire). So I went ahead and pulled the distributor, found the gear to be worn. Installed a new gear and put it back together. Took it for a drive and it runs great again.

thanks again

Sidom
Veteran / Moderator
Sidom profile image

Jul 18, 2010, 7:40 PM

Post #4 of 4 (1544 views)

Re: 4.3l running rough at 65mph	Sign In

Hey....Thx 4 coming back and letting us know what fixed it.

You might help someone else out with the same problem down the road.

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