'74 engine won't turn off
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
'74 engine won't turn off
You can have a condition called "engine run-on" or "dieseling" where the engine can continue to run (poorly) without an ignition source. Essentially, there are some carbon deposits in the combustion chamber that stay hot enough to [barely] fire the air/fuel charge, once it is fully compressed at TDC. This was a common problem when engine timing was significantly retarded for emissions purposes. Car makers came up with 'creative' approaches to put a load on the engine so that it would shut down (not enough power generated when dieseling to overcome the applied load). For example: If the car had A/C, the compressor may have been engaged for a few seconds after the ignition was turned to OFF.
"Dieseling" is easily differentiated from a normal running engine, as it runs very poorly with spotty ignition firings, etc.
If the engine is running normally, power is getting to the ignition system somehow.
"Dieseling" is easily differentiated from a normal running engine, as it runs very poorly with spotty ignition firings, etc.
If the engine is running normally, power is getting to the ignition system somehow.
Tomorrow , I will get a new fan control/relay. The hunt goes on !
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
'74 engine won't turn off
You can have a condition called "engine run-on" or "dieseling" where the engine can continue to run (poorly) without an ignition source. Essentially, there are some carbon deposits in the combustion chamber that stay hot enough to [barely] fire the air/fuel charge, once it is fully compressed at TDC. This was a common problem when engine timing was significantly retarded for emissions purposes. Car makers came up with 'creative' approaches to put a load on the engine so that it would shut down (not enough power generated when dieseling to overcome the applied load). For example: If the car had A/C, the compressor may have been engaged for a few seconds after the ignition was turned to OFF.
"Dieseling" is easily differentiated from a normal running engine, as it runs very poorly with spotty ignition firings, etc.
If the engine is running normally, power is getting to the ignition system somehow.
"Dieseling" is easily differentiated from a normal running engine, as it runs very poorly with spotty ignition firings, etc.
If the engine is running normally, power is getting to the ignition system somehow.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Very wierd. Never came across that one. I suspect there may be some 'adjustments' to the wiring which have allowed that to happen; but I do not know that it could not happen with correct wiring.
Le Mans Master
Joined: Aug 2006
Posts: 7,431
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,754
From: Charlotte NC
Somebody has done something to the wiring somewhere...or the ignition circuit is touching the circuit he found to the culprit.
I have come across some Corvette where it is multiple problems that all link together to screw up the electrical system.
DUB
I have come across some Corvette where it is multiple problems that all link together to screw up the electrical system.
DUB
