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#1442748 Sat Feb 26 2022 03:28 PM
Joined: Jun 2010
Posts: 21
Good morning boys and girls, I have a '51 3800 Panel with a 350/T5. Runs fabulous. My problem is shutting it off. The motor will continue for 3 seconds after I turn off the key. It's not "Dieseling". Any suggestions?
Thanks in advance.
Ed Lupardo

Ed Lupardo #1442749 Sat Feb 26 2022 03:47 PM
Joined: Mar 2007
Posts: 5,072
Leo Offline
Ed, I would suggest posting this in the engine shop. A 350 engine doesn't really relate to a 1951 panel, likely more people will see your post.

Ed Lupardo #1442753 Sat Feb 26 2022 04:51 PM
Joined: Apr 2005
Posts: 3,073
Does the truck have an electric fan? If so it will provide current till fan motor dies down. A diode or switched relay will solve.

Ed Lupardo #1442759 Sat Feb 26 2022 07:20 PM
Joined: May 2005
Posts: 8,976
Sir Searchalot
I will assume with your self diagnosis that you do not have a carburetor? That is the only way you could say it's not dieseling.

Before we get the necessary info/history/back story and motor accessories, the first answers will be dieseling or too high of an idle....or a fancy "hot" spark plug. There are other heat related causes. Lean/rich/carbon/plugs/heat riser/exhaust leaks/timing.....also a bad ignition switch or wire or a miswire.

1. Is this a new motor install? or rebuild?
2. Does it have headers? Do they leak?
3. Been running ok until just recently this started happening?
4. Have you just completed any motor work/replacement of any parts. Done any timing?
5. Carburetor? Carburetor model? Hot rod motor parts?
6. Any wiring done recently?
7. Spark plug part number? Stock coil?
8. Mileage on motor?
9. Happens after short runs and long runs? If you start it up cold and run for two minutes, does it still run on?

Ed Lupardo #1442791 Sun Feb 27 2022 02:04 AM
Joined: Jun 2010
Posts: 295
A Lot more information is needed to come up with an idea. What are you using for ignition? Points/condensor/coil? HEI? Aftermarket stuff like MSD?

1949 Chevy 3600
1975 W-25 Hurst Olds
1991 Chevy Silverado
1970 GMC 1/2 ton Fleetside
2010 Chevy Silverado
I'm a GM man!
Ed Lupardo #1442796 Sun Feb 27 2022 02:46 AM
Joined: Oct 2021
Posts: 770
Timing too far advanced for the octane rating of the fuel you're using?

1939 Packard Standard Eight Coupe
1950 Chevrolet 3100
1956 Cadillac Coupe de Ville
1966 Oldsmobile Toronado
1966 Ford Mustang
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Ed Lupardo #1442816 Sun Feb 27 2022 02:12 PM
Joined: Nov 2002
Posts: 2,386
Carburetion specialist
Shut it off 3 seconds before you are ready to shut it off???? wink

Sorry, could not resist.


Good carburetion is fuelish hot air
The most expensive carburetor is the wrong one you attempt to modify
If you truly believe "one size fits all" try walking a mile in your spouse's shoes!
carbking #1442860 Sun Feb 27 2022 07:16 PM
Joined: May 2005
Posts: 8,976
Sir Searchalot
Originally Posted by carbking
Shut it off 3 seconds before you are ready to shut it off???? wink

Sorry, could not resist.

Very good Jon grin Now that you say that, it dawned on me that 3 seconds could be really close to normal to stop the rotating mass after the last plug fires and sends a power stroke. (Momentum).

Ed Lupardo #1442909 Mon Feb 28 2022 01:16 AM
Joined: Feb 2004
Posts: 25,002
Kettle Custodian (pot stirrer)
This sounds like a feedback from the alternator. Try running on just the battery with all the wiring disconnected from the charging system and see if the run-on happens.

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