1995 Chev K1500 - 4.3L Engine Bucking

[Tim Martin]

I got this 95 Chevy K1500 truck with a 4.3L engine and a manual 5 speed trans. Got 130,000 miles on it an the issue is that at low rpm under load, the engine has a nasty intermittant bucking to it. Once it gets above a certain rpm range it runs fine. No CEl, no codes, no miss, fuel pressure 13-15 psi at idle, vacuum is 19" at idle, runs decent otherwise. I am suspicious of a coil pickup in the distributor but I am wanting to know how to check the coil pickup out. Does anybody have a way to do this or am I chasing the wrong thing?

[steven kiser]

If I had a buck for every dist of this vintage I could have a nice weekend away. Rust on bottom plate, replace, plate loose, replace, oil in distributer, replace, shaft walk, replace. Only other thing I would do is to un plug the EGR and try it first.

[Tim Martin]

At first I thought it was the EGR valve so I installed a new one plus the solenoid with no change in performance.

[sbebenelli]

Just plug your computer into it and replace what it says is bad.

I know I've replaced a lot of distributor shafts in these because the magnet gets weak. I always but a new pick up in at the same time. Seems like the last time I needed a shaft I couldn't find one so I'm not sure if they are available anymore. I hate reman distributors but sometime you have no choice.

[Tim Martin]

I agree with the idea of replacing these faulty distributors. Is there any way to test the magnet?

[steven kiser]

A few other points here. I've had more than my fair share of issues with the coil wire shorting out, was this tuned by you and the issue remained? I had a Blazer in the shop with a similar issue and after grilling the customer found out the issue started soon after it was tuned up. I found a spark plug that had been dropped and the gap was way off. Now my snappy scanner has graphing availability so I would take a "movie" when it's doing it and then sit at my desk going over the information. I'm not sure on this one and haven't refreshed my memory but I think this has the spider injector set up and I've had situations like this one where one of the injector lines had unsnapped and pulled out of the port just enough so it would be fine until the vacuum zeroed out and the suction wasn't strong enough to suck the fuel into the cylinder.

[Tim Martin]

This one has a throttle body fuel injection. I replaced the ignition module and coil pickup an the problem still remains. Very frustrating.

[sbebenelli]

I agree with the idea of replacing these faulty distributors. Is there any way to test the magnet?

Sorry it took so long to get back to you. I know the magnets will be all cracked if it's bad but you can't see it unless you pull the shaft out of the distributor. The symptom I seemed to always have is the truck would die at idle when the magnets get weak. I don't know if I've seen it cause a bucking.

Have you replaced the plugs and wires? It wouldn't just be a bad wire would it?

[Tim Martin]

Have you replaced the plugs and wires? It wouldn't just be a bad wire would it?

Well, that's my next plan.