engine stays running after key off - Chevelle Tech
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post #1 of 10 (permalink) Old May 3rd, 09, 10:01 AM Thread Starter
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engine stays running after key off

What causes an engine to stay running for a few seconds after the key is shut off. No it is not desieling it is running like normal for up to 8-10 seconds then turns off. This is a new 350 that was put into a cutlass. Any ideas?

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post #2 of 10 (permalink) Old May 3rd, 09, 11:28 AM
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Re: engine stays running after key off

Most likely your alternator is backfeeding through the system. Try disconnecting the small connector on the alternator, and then start and shut off the car. If you changed any circuitry, or added anything that is probably what is allowing it. I have seen this on AMCs.
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post #3 of 10 (permalink) Old May 3rd, 09, 11:54 AM
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Re: engine stays running after key off

I did this years ago in a camaro. I wired the electric cooling fans to a power source in the fuse panel, turned out to be another accessory terminal for the ignition. The engine would stay running untill the fans stopped turning.

Somewhere the power is backfeeding to your ignition, I'm guessing HEI dist.?

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post #4 of 10 (permalink) Old May 3rd, 09, 12:42 PM
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Re: engine stays running after key off

also make sure your ground wire is on from the block to the firewall
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post #5 of 10 (permalink) Old May 3rd, 09, 2:14 PM
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Re: engine stays running after key off

If you are running an MSD box, you need to install the Diode they included. I think it goes inline between the box and the coil. The capacitance of the box may continue feeding the coil after the power is cut. The diode allows voltage in only one direction so it will block any backfeed after you shut down.

If you're not running an MSD box, then.... I dunno .

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post #6 of 10 (permalink) Old May 3rd, 09, 6:18 PM
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Re: engine stays running after key off

Quote:
Originally Posted by BigRat09 View Post
If you are running an MSD box, you need to install the Diode they included. I think it goes inline between the box and the coil. The capacitance of the box may continue feeding the coil after the power is cut. The diode allows voltage in only one direction so it will block any backfeed after you shut down.

If you're not running an MSD box, then.... I dunno .

Electronics scare me.

Timing might be off
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post #7 of 10 (permalink) Old May 3rd, 09, 6:41 PM Thread Starter
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Re: engine stays running after key off

OK lets start with ground cable is attatched to block and firewall. Same alternator was used just changed motors, olds to chevy. No msd. Fans are wired to turn on and off with ign. Changed dist from olds to chevy.

I will try all suggestions just to cover my bases. Any other ideas we will try till it is fixed. Thanks

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post #8 of 10 (permalink) Old May 3rd, 09, 7:10 PM
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Re: engine stays running after key off

Quote:
Originally Posted by deck6972 View Post
OK lets start with ground cable is attatched to block and firewall. Same alternator was used just changed motors, olds to chevy. No msd. Fans are wired to turn on and off with ign. Changed dist from olds to chevy.

I will try all suggestions just to cover my bases. Any other ideas we will try till it is fixed. Thanks
Appears your running electric fans, are wired though relays? If not they should.

If they simply wired into the ignition circuit the electric fans act like a generator once the power field is removed and they will generate power as long they are spinning fast enough which will feed back though the circuit and provide enough power for the dist/ignition the allow the engine to run until the fans stop. properly wired relays not only allow to pull power from a high circuit such as directly from the battery, but isolate will ignition circuit from the feedback.

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post #9 of 10 (permalink) Old May 3rd, 09, 8:49 PM
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Re: engine stays running after key off

Quote:
Originally Posted by shonuff View Post
Timing might be off
I agree, adjust your distributor and turn the car on and off see what happens.
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post #10 of 10 (permalink) Old May 3rd, 09, 9:18 PM
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Re: engine stays running after key off

Quote:
Originally Posted by cachevelle66 View Post
Appears your running electric fans, are wired though relays? If not they should.

If they simply wired into the ignition circuit the electric fans act like a generator once the power field is removed and they will generate power as long they are spinning fast enough which will feed back though the circuit and provide enough power for the dist/ignition the allow the engine to run until the fans stop. properly wired relays not only allow to pull power from a high circuit such as directly from the battery, but isolate will ignition circuit from the feedback.
Ya. What he said. Every fan mnf. suggests a relay... notsure why until now. Makes absolute sense though.

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