Help with Ignition - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Madbomber88 · 01-06-2007, 01:46 PM

Just finished installing a TBI conversion with painless harness into my 72 K20.
Started her up and she runs fine but does not turn off. You can take the key out and unhook the battery, but only way to get her to shut off is to unplug the coil plug.

I already replaced the ignition cylinder and that made no difference. I know this must be something very simple.
Any help is much appreciated.
Thanks

kyull67 · 01-06-2007, 02:32 PM

don't know, but I'll bump it to the top for you.

Longhorn Man · 01-06-2007, 02:34 PM

Do you have an electric fan hooked up? It sounds like it's turned on when you shut off the engine and it is backfeeding.. working as an alt. try unplugging the fan, then fire up the truck ans shut it off.

Madbomber88 · 01-06-2007, 03:07 PM

No, I don't have a fan, but could something else be doing the same thing?
What is it that sends the message to shut the engine off? I assume it is something that stops sending power to the coil?

**Boog** · 01-06-2007, 11:54 PM

[Started her up and she runs fine but does not turn off. You can take the key out and unhook the battery, but only way to get her to shut off is to unplug the coil plug.]
Try unhooking the alternator plug. It has to be backfeeding current from a power generator or cooling fan one in order to keep running with the battery disconnected. I assume it was fine before the conversion? May need to call the tech help line at painless wire.

e rock · 01-07-2007, 02:51 AM

Yup - alternator is backfeeding the coil. I haven't done it, but it's a pretty common issue when people upgrade alternators. The fix is to install a little light bulb or diode. I can't remember the details off-hand... [off to check the old bookmark file]

01-06-2007, 01:46 PM	#1
Madbomber88 Active Member Join Date: Mar 2004 Location: Virginia Posts: 169	Help with Ignition Just finished installing a TBI conversion with painless harness into my 72 K20. Started her up and she runs fine but does not turn off. You can take the key out and unhook the battery, but only way to get her to shut off is to unplug the coil plug. I already replaced the ignition cylinder and that made no difference. I know this must be something very simple. Any help is much appreciated. Thanks __________________ 71 Blazer CST 72 K20 Capt USAF

01-06-2007, 02:32 PM	#2
kyull67 Registered User Join Date: Nov 2006 Location: Springfield/Kansas City Posts: 1,842	Re: Help with Ignition don't know, but I'll bump it to the top for you. __________________ The first '67 The current '67 '63 Biscayne

01-06-2007, 02:34 PM	#3
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,690	Re: Help with Ignition Do you have an electric fan hooked up? It sounds like it's turned on when you shut off the engine and it is backfeeding.. working as an alt. try unplugging the fan, then fire up the truck ans shut it off.

01-06-2007, 03:07 PM	#4
Madbomber88 Active Member Join Date: Mar 2004 Location: Virginia Posts: 169	Re: Help with Ignition No, I don't have a fan, but could something else be doing the same thing? What is it that sends the message to shut the engine off? I assume it is something that stops sending power to the coil? __________________ 71 Blazer CST 72 K20 Capt USAF

01-06-2007, 11:54 PM	#5
Boog laying low Join Date: Mar 2001 Location: Searcy, Ark. USA Posts: 13,535	Re: Help with Ignition [Started her up and she runs fine but does not turn off. You can take the key out and unhook the battery, but only way to get her to shut off is to unplug the coil plug.] Try unhooking the alternator plug. It has to be backfeeding current from a power generator or cooling fan one in order to keep running with the battery disconnected. I assume it was fine before the conversion? May need to call the tech help line at painless wire. __________________ Boog 69 Chevy stepside, 358/T350, 4.11 posi, 4.5/4 drop, rallys, poboy driver primer is finer 91 Chevy sportside, Tahoe, Yukon & GMC Crewcab All GM..'nuff said. I stand for the flag and kneel at the cross

01-07-2007, 02:51 AM	#6
e rock Registered User Join Date: Nov 2006 Location: Monroe, WA Posts: 87	Re: Help with Ignition Yup - alternator is backfeeding the coil. I haven't done it, but it's a pretty common issue when people upgrade alternators. The fix is to install a little light bulb or diode. I can't remember the details off-hand... [off to check the old bookmark file]



Register or Log In To remove these advertisements.

Register or Log In To remove these advertisements.