Dieseling and Drifting

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Sep 30, 2008 | 05:50 AM

Caleb H

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From: Pennsylvania

Dieseling and Drifting

Truck: 1983 Ford F150, 4.9L I6, C6 Transmission

Dieseling: Okay, why does my truck diesel? It only happens occasionally, and it's never too bad, but it bothers me and I know it's not good for the truck. I know that it can be caused by the build-up of carbon in the engine, so I'm wondering: could that be from using 10% ethanol gas?

Drifting: This one's a little less self-explanatory. On hot summer days, after driving my truck for about half an hour, it starts to pull left. After an hour is passed, it starts to pull so hard that it gets dangerous to drive. If I park it and shut it off for an hour, and it cools down a bit, it is totally and completely fine, no work involved. What could be causing this? The suspension? Tire pressure? Heating of the steering column? I'm at a loss

Sep 30, 2008 | 06:46 AM

IcemanV8

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The second one sounds like your caliper could be getting hot and locking up.

Sep 30, 2008 | 07:00 AM

f100jim

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I agree with IcemanV8. Sounds like a stuck caliper, most likely the left caliper.

My 82 sometimes diesels when I shut it off. I always put it in 1st and ease the clutch out until the RPM drops 100 or 200 revs, then turn it off. With the automatic, just leave it in drive, turn it off, then shift to park. This does not cure the problem, but it stops the dieseling. Short of pulling the head and removing all of the carbon from the chamber, or running much higher octane gas (which isn't available on the street anymore) this is an easy "solution".

Sep 30, 2008 | 10:02 AM

ctubutis

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From: Denver Metro Area, CO

Quote:

Originally Posted by Caleb H

could that be from using 10% ethanol gas?

IIRC there's a device on the carb that closes the throttle plate upon shutdown in order to
prevent dieseling, you might search through the archives and/or look at illustrations in a
service manual or parts book or some such to see what I'm referring to. I also seem to
recall the ignition timing being a possible contributor to this as the engine was calibrated
out of the factory to pass EPA emissions tests rather than for performance.

We here in Colorado have been using the ethanol fuel in the non-summer months for
something close to 20 years now, I'd think I would have heard by now of any adjustments
needed to accommodate it.

-ct

Sep 30, 2008 | 11:03 AM

srercrcr

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Yea, I think there's a solenoid that triggers and slams the throttle plate shut so no air can enter....no air, no combustion.

Sep 30, 2008 | 11:26 AM

f100jim

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Quote:

Originally Posted by srercrcr

Yea, I think there's a solenoid that triggers and slams the throttle plate shut so no air can enter....no air, no combustion.

Yep, it is usually called an "anti-dieseling solenoid". Mine has it and it is working and adjusted properly. I think the problem with the 300 is that the log manifold holds enough fuel and air that, with a hot engine, it will still try to keep running for a second or two, even with the carb slammed shut.

However, there is the possibility that the throttle stop screw is not adjusted correctly. There is a screw that sets the fully closed position - it is supposed to be adjusted so that it stops the throttle just at the point where the butterflies are fully closed. It keeps the butterflies from jamming from being closed too tightly. Someone may have mistaken this for the idle speed setting screw and may have cranked it in a few turns to set the idle speed. That will keep throttle open even when the solenoid de-energizes.

Sep 30, 2008 | 01:49 PM

mchbts

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I have had the same dieseling problem with my 300. It only does it when the motor is real hot- I hauled a lot of hay wagons this summer with my F150 and just about every time I shut it off it would diesel. I bought a bunch of carb cleaner and marvel mystery oil and kept dumping that in and it stopped and has run great since- i still try to run the oil and carb cleaner every couple of tanks and I have had no more dieseling. As for the Ethanol- i tried it- i know its cheaper but i switched back to regular- the truck runs alot better and i actually do get about 3mpg better with regular.