dieseling

It could be bad gas, too low of an octane rating, plugs that are too hot, a high idle, high engine temp. incorrect timing or carbon buildup that is getting hot and causing the engine to "run on". One temporary solution, if you have an automatic transmission, is to keep it in gear until you shut the engine off; then shift into park.

Group: alt.trucks.chevy Date: Thu, Mar 16, 2006, 8:16am (EST-3) From: snipped-for-privacy@juno.com

I see several posts on this topic here, but please let me frame my question around my particular circumstances...

We bought an '86 Chevy truck a month or so ago. No problems at all until the last few days... I cut the engine off earlier this week and it dieseled for a few seconds before shutting off. Then last night we drove it again and it dieseled for at least a minute or two before I finally got it to shut off. Then it did the same thing when we drove it again later.

Since this is a sudden, recent problem, would it likely be due to the gas I'm using? I've been filling it up with 87 since we bought it (don't know what the guy before me used), but wondering if maybe the last tank I got was bad or if I should be upgrading to a higher octane. =A0=A0Seems like I should try that before anything else, but would appreciate any advice... thanks! =A0 CAC

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% "So why do I drive a big SUV? It's because I have to haul numerous people and things to places." ~ R. Lee Baxton ~

Here's my guess - there should be a "dashpot" at the throttle body. When the key is turned off, it closes the throttle plates to less than idle. If its not working, the engine still gets some air (as if it were still idling) and causes the detonation.

There should be a solenoid on the side of the carb, key on it will bump the throttle linkage to idle position, key off it closes the throttle plate all the way. I would look at this device, as well as using some top cylinder cleaner as there is probably carbon build up on the pistons as well. Key off there is no spark, so the ignition source has to be something hot enough to ignite the fuel mix sucked into the cylinder. Carbon build up is good at that.

Whitelightning

Thanks for everyone's feedback. I bought some fuel additive that is supposed to help clean out the carb deposits, and will put that in and fill up with high octane today and see how that does. Truck was running real rough yesterday and wasn't getting much power when I drove home from work -- which has me worried -- but a little later started up fine and seemed to be running as smoothly as usual (though I didn't drive it). The solenoid on the side of the carb seems another likely problem, since it does tend to run on for several minutes after shutoff, not just a few seconds. CAC

Whitelightn> There should be a solenoid on the side of the carb, key on it will bump the

Update: truck didn't start that day. Ended up having it towed. Mechanic at first thought it needed new spark plugs, but then it was still having trouble starting. Then he thought it was the choke, so he fiddled with that and it was still having problems. Today he's putting on a new (rebuilt) carburetor. CAC

snipped-for-privacy@juno.com wrote: