'74 engine won't turn off
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
'74 engine won't turn off
I turned the key to Lock , transmission in Park and the engine kept running.
The only way to shut the engine off is to shift into Reverse or Neutral. I am at a lost to figure it out.
The only way to shut the engine off is to shift into Reverse or Neutral. I am at a lost to figure it out.
Burning Brakes
Joined: Oct 2012
Posts: 1,152
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Is it actually running or is it "run-on" (self combustion from pre-ignition detonation)?
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
The ONLY thing I can think of is that the ignition coil is still getting power even with the key off....and if my memory serves me correctly...you still have a points distributor...which means that the resistance wire that goes to the ignition coil also goes down to your starter and it can be touching the battery power wire.....thus...keeping your ignition alive and allowing your engine to keep running even though you turned the key off.
DUB
DUB
Last edited by DUB; May 10, 2017 at 06:59 PM.
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The ONLY thing I can think of is that the ignition coil is still getting power even with the key off....and if my memory serves me correctly...you still have a points distributor...which means that the resistance wire that goes to the ignition coil also goes down to your starter and it can be touching the battery power wire.....thus...keeping your ignition alive and allowing your engine to keep running even though you turned the key off.
DUB
DUB
I actually did that one time many, MANY years ago..
Racer
Joined: Aug 2015
Posts: 373
Likes: 170
From: South Bend IN
Mine started doing the same thing a couple of weeks ago. (75 w/HEI)
I was thinking that it just wanted out of the garage.
I disconnected the two wire plug at the alternator, and it died.
Replacing the alternator soon, if it continues I will check back, and see what you found.
Have a Great Day,
Bill
I was thinking that it just wanted out of the garage.
I disconnected the two wire plug at the alternator, and it died.
Replacing the alternator soon, if it continues I will check back, and see what you found.
Have a Great Day,
Bill
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
'74 engine won't turn off
The ONLY thing I can think of is that the ignition coil is still getting power even with the key off....and if my memory serves me correctly...you still have a points distributor...which means that the resistance wire that goes to the ignition coil also goes down to your starter and it can be touching the battery power wire.....thus...keeping your ignition alive and allowing your engine to keep running even though you turned the key off.
DUB
DUB
But , yes , there is still voltage at the coil with the key in off/lock position.
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
Mine started doing the same thing a couple of weeks ago. (75 w/HEI)
I was thinking that it just wanted out of the garage.
I disconnected the two wire plug at the alternator, and it died.
Replacing the alternator soon, if it continues I will check back, and see what you found.
Have a Great Day,
Bill
I was thinking that it just wanted out of the garage.
I disconnected the two wire plug at the alternator, and it died.
Replacing the alternator soon, if it continues I will check back, and see what you found.
Have a Great Day,
Bill
I guess I will have to begin tracing wires, can't give up and fix a kill switch.
I have had this car for 41 years and have kept it all original.
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Safety Car
Joined: Apr 2006
Posts: 4,057
Likes: 421
From: BC
I'm not much on electrics but if your coil is still powered with the ignition switch off it either has to be coming from the starter to coil bypass wire that supplies a full 12 volts during start or the ignition switch itself. I know you checked the starter to coil bypass wire but try disconnecting it from the outside terminal on the starter, then start the car and then see if your problem goes away. It could be in the starter solenoid. If not the ignition switch is my guess....
Le Mans Master
Joined: Aug 2006
Posts: 7,421
Likes: 1,558
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
'It turns off in reverse or neutral'.
How can that be?
I have to stick around as this is interesting.
How can that be?
I have to stick around as this is interesting.
Race Director
Joined: Apr 2009
Posts: 19,294
Likes: 2,753
From: Charlotte NC
Knowing that you still have battery voltage at the coil when the key is turned off....I still might remove the wire on your solenoid that goes to the coil. And then see if it goes away.
I completely missed that Pete.
I have to wait for more clarification on this due to it makes no sense...unless someone has played around with the wiring.
DUB
I have to wait for more clarification on this due to it makes no sense...unless someone has played around with the wiring.
DUB
Le Mans Master
Joined: Oct 2006
Posts: 7,123
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Is it possible the park interlock cable is keeping the key from going all the way to OFF/LOCK? That could be why the coil is powered when the key is OFF?
Le Mans Master
Joined: Aug 2006
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From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi again mrobert,
1974 has a 'seatbelt/starter interlock, does yours work?
Do you have to buckle up before the car will start?
Pete.
1974 has a 'seatbelt/starter interlock, does yours work?
Do you have to buckle up before the car will start?
Pete.
Drifting
Joined: Apr 2011
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From: Deerfield Illinois
2022 C3 of the Year Finalist - Modified
C3 of Year Finalist (appearance mods) 2019
I have heard of this before, car kept running on after shutoff and the ignition switch was the culprit. Broke internally was a 1969 model though
Thread Starter
8th Gear
Joined: Oct 2006
Posts: 8
Likes: 0
"74 engine won't turn off
I'm not much on electrics but if your coil is still powered with the ignition switch off it either has to be coming from the starter to coil bypass wire that supplies a full 12 volts during start or the ignition switch itself. I know you checked the starter to coil bypass wire but try disconnecting it from the outside terminal on the starter, then start the car and then see if your problem goes away. It could be in the starter solenoid. If not the ignition switch is my guess....
The first thing I did was get a new ignition switch, no help. Next, I got a new key/lock cylinder, no help. Never had to have the seat belts connected to start the car, but I tried ... still won't stop running in Park.
Forgot to add one thing... no more voltage at coil with key in lock/off and trans in park position . Still have to pull coil wire.
Must be in the wiring somewhere, I can't / won't give up. It is embarrassing
to have a Corvette that doesn't perform correctly.
Forgot to add one thing... no more voltage at coil with key in lock/off and trans in park position
Last edited by mrobert; May 12, 2017 at 11:30 AM. Reason: forgot something to add
Safety Car
Joined: Apr 2006
Posts: 4,057
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From: BC
The only other thing I can think of is do you have a wire plugged into the IGN terminal on the under dash fuse box that might be supplying 12v to the coil? Also, is there any other wire running to the positive side of the coil besides the one terminal holding the two ignition wires? Did you also check the ignition switch connector wire terminals?
Le Mans Master
Joined: Aug 2006
Posts: 7,421
Likes: 1,558
From: mount holly NC
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
I removed the outside wire on the starter solenoid, started the motor turned the key to OFF ... motor kept running, had to pull coil wire.
OK, that eliminates the yellow wire feeding back from the solenoid.
Forgot to add one thing... no more voltage at the coil with the key in lock/off and trans in the park position. Still, have to pull coil wire.
Must be in the wiring somewhere. DOE!
OK, that eliminates the yellow wire feeding back from the solenoid.
Forgot to add one thing... no more voltage at the coil with the key in lock/off and trans in the park position. Still, have to pull coil wire.
Must be in the wiring somewhere. DOE!
Are you testing between the coil + and ground?
Interesting about the seat belt interlock.
Seems like yours was bypassed previously.
Related to the new problem?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
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.
Last edited by 7T1vette; May 12, 2017 at 06:10 PM.