Help Car won't turn off
Thread Starter
Intermediate
Joined: Oct 2002
Posts: 39
Likes: 0
From: McAllen TX
Help Car won't turn off
Whenever I turn the ignition switch to the off position the engine won't shut down, This goes on for a couple of seconds until it finally dies, but sometimes the car just won't shut down and starts shaking really bad. This is very frustrating please help. 
Race Director
Joined: Dec 2000
Posts: 10,896
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From: CO
Something in the cylinder may be hot and causing the mixture to ignite from something other than the sparkplug.
First thing that comes to my mind is carbon deposits. This increases the comp ratio and may cause it to combust, or the deposits are hot and causing it to combust. Could be from it running rich. Its called diseling. I have heard that you can pour a bit of water down the carb slowly and it will clean things out.
This is just a thought, im sure there will be other ideas. I bet Lars knows
First thing that comes to my mind is carbon deposits. This increases the comp ratio and may cause it to combust, or the deposits are hot and causing it to combust. Could be from it running rich. Its called diseling. I have heard that you can pour a bit of water down the carb slowly and it will clean things out.
This is just a thought, im sure there will be other ideas. I bet Lars knows
Burning Brakes
Joined: Dec 2004
Posts: 918
Likes: 5
From: Gainesville FL
I had this problem when I got my car. The electric fan had been wired into the distributor circuit so it would act as a generator after the key was shut off and keep the car running for another 5 seconds or so until it spun down. There are other things that might also be causing your problem, but you might check this if you have an electric fan.
Melting Slicks
Joined: Sep 2004
Posts: 2,655
Likes: 19
If you're referring to run-on or dieseling. It's caused by high idle speed, too much ignition advance, carbon build up in the cylinders. Too much heat in the cylinders ignites fuel without spark. It also could be having detonation problems which will waste an engine.
Gary
Gary
Melting Slicks
Joined: May 2002
Posts: 2,431
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From: Florida
Originally Posted by Vette Gator
I had this problem when I got my car. The electric fan had been wired into the distributor circuit so it would act as a generator after the key was shut off and keep the car running for another 5 seconds or so until it spun down. There are other things that might also be causing your problem, but you might check this if you have an electric fan.
I had this happen when I had elec. fan.Jim
Drifting
Joined: Sep 2004
Posts: 1,532
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From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
Originally Posted by Garys 68
If you're referring to run-on or dieseling. It's caused by high idle speed, too much ignition advance, carbon build up in the cylinders. Too much heat in the cylinders ignites fuel without spark. It also could be having detonation problems which will waste an engine.
Gary
Gary
High idle speed was the cause of mine.
Race Director
Joined: Oct 2000
Posts: 15,048
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From: central FL, near the beach.
Originally Posted by duliz
Whenever I turn the ignition switch to the off position the engine won't shut down, This goes on for a couple of seconds until it finally dies, but sometimes the car just won't shut down and starts shaking really bad. This is very frustrating please help.
Race Director
Joined: Nov 1999
Posts: 10,643
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From: Foxfield CO 1970 Convertible
Whether or not you have carbon deposits, high idle, bad timing, etc., etc., the engine will stop instantly if the throttle closes completely. If the intake closes completely, neither air nor gas mixture can get to the cylinders. This is an easy fix.
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Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
Originally Posted by Z-man
Whether or not you have carbon deposits, high idle, bad timing, etc., etc., the engine will stop instantly if the throttle closes completely. If the intake closes completely, neither air nor gas mixture can get to the cylinders. This is an easy fix.
-Chris
Safety Car
Joined: Feb 2002
Posts: 4,286
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From: Guam
Originally Posted by jimvette999
I had this happen when I had elec. fan.Jim
If you want to fix it, just run a clean power supply from the battery to the relay, then put the trigger line (more than likely a tap in to your vehicle ignition line) to the relay and connect your power feed from the relay to the fan.
You should then be ready to go.....
Last edited by Sharky Guam; Apr 4, 2005 at 07:01 PM.
Race Director
Joined: Nov 1999
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From: Foxfield CO 1970 Convertible
Originally Posted by LiveandLetDrive
I have to disagree with that, my engine runs pretty well at idle.. by definition the throttle is completely closed. I'd be interested to know how you can stop any and all A/F from reaching the cylinders. In any case, treat the disease, not the symptoms.
-Chris
-Chris
I agree that this wouldn't clean cylinder heads, carbon deposits, or fix bad timing, but it WILL stop the irritating run-on after the key is removed. In fact, if you have high compression, the engine will stop in less than one revolution from an idle.
Melting Slicks
Joined: Jul 2002
Posts: 3,000
Likes: 22
From: Boulder Creek California
Ah, true. I'm running a Speed Demon and recommended closed position still reveals a little of the transfer slot. So basically, any carb without an idle-stop solenoid is going to have some kindof air available to the engine.
Melting Slicks
Joined: Jun 2001
Posts: 2,429
Likes: 14
From: CA
My Vette will do the same thing because of the rich mixture & 10:1 CR. I always shut it down in gear with a slight load (By letting the clutch out a little) - Just one of the things you need to do when you run today's gas in a built motor. 
Advanced
Joined: Feb 2005
Posts: 84
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From: Santa Monica California
Two mechanics who work on my car regularly told me it's (1) rich fuel mixture; (2) high compression due to engine mods and (3) modern gas sucks. I always let the clutch out a little to kill the dieseling. I also noticed a big decrease in dieseling when I started adding Max Lead 2000 to get rid of the the fumes (which it does a good job of dealing with as well). Since I use the stuff it often doesn't diesel at all and if it does it's less than it did before.
Le Mans Master
Joined: May 2000
Posts: 6,493
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From: Bloomington MN
Cruise-In II Veteran
Originally Posted by Z-man
If your car can idle, your throttle is cracked or air is entering through an idle passage. Some carbs have a slot to allow air through - not much is needed - maybe the thickness of a fingernail, and it may appear that the throttle is completely closed. When you shut off the key, the throttle plates should close *completely* or you can get run-on. In 1976, the carbs came with an idle stop solenoid which cracks the throttle while the key is on - if this is the original setup, perhaps the solenoid is out of adjustment. Another possibility is a gasket leak allowing air to get in. I'd also check the return springs to make sure the throttle plates snap shut.
I agree that this wouldn't clean cylinder heads, carbon deposits, or fix bad timing, but it WILL stop the irritating run-on after the key is removed. In fact, if you have high compression, the engine will stop in less than one revolution from an idle.
I agree that this wouldn't clean cylinder heads, carbon deposits, or fix bad timing, but it WILL stop the irritating run-on after the key is removed. In fact, if you have high compression, the engine will stop in less than one revolution from an idle.
