engine stays running after key off [Archive] - Chevelle Tech

: engine stays running after key off


deck6972
May 3rd, 09, 9:01 AM
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?

Buh Waaaa
May 3rd, 09, 10:28 AM
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.

66SSFan
May 3rd, 09, 10:54 AM
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.?

bln
May 3rd, 09, 11:42 AM
also make sure your ground wire is on from the block to the firewall

BigRat09
May 3rd, 09, 1:14 PM
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 :rolleyes:.

Electronics scare me.

shonuff
May 3rd, 09, 5:18 PM
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 :rolleyes:.

Electronics scare me.


Timing might be off

deck6972
May 3rd, 09, 5:41 PM
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

cachevelle66
May 3rd, 09, 6:10 PM
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.

rock72chevelle
May 3rd, 09, 7:49 PM
Timing might be off

I agree, adjust your distributor and turn the car on and off see what happens.

BigRat09
May 3rd, 09, 8:18 PM
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.:yes: