Technical 350 Runs couple seconds aftyer key turned off

Have 350 with Holly 4 barrel. Installed new Painless harness and key switch at same time. Just does it when car is warmer up good not when cold. It will run couple seconds after key is turned off, then shut off. Checked timing recommended by Painlees tec support. Base idle timing was 10 degrees, so I tried upping it to 13 degrees, made it start hard when hot. After some research I found information on older 350 with Holley carb and having a HEI distributor to set the base idle timing at 8 degrees which I did. It starts cold or hot good and idles good now but still delays on shut off when hot. One thing that makes me think some in wiring is when I tried starting once before resetting the time and it didn't start, I the turned key back off and electric fuel pump kept running for a couple seconds then shut down.

 

It´s called dieseling, glowing hot spots in the combustion chamber ignite the A/F mixture, which keeps the engine running even with the ignition off... often carbon deposits on worn, oil burning engines can cause this.... how fresh is you engine?

 

Does it have an electric fan? If it does (and it's running at the time) the fan will act like a generator and supply some voltage to keep things running.

 

Pull the intake and clean out all the carbon.

 

An Msd ignition does this very thing on my pickup.

 

A fan relay will stop this from happening.

 

And the ol'e 1 wire alternator.............. Threads abound on the subject.

 

Yes it does and that sounds right because it does it only when hot.

 

OK don't have a relay have it setup with 10 gauge direct like instructions suggest

 

Yep one wire 63 amp

 

Don't think it's dieseling to smooth, growing up in the 60's remember what that sounded like.

 

Huh?!?! Carbon in the intake?!?!

 

Quick test would be to unplug the fan or alt (most likely the fan) when it's doing it and trying it again.

 

Will try that, easy try

 

A simple fix(not really a fix,but a temporary stop gap measure till problem is fixed) is to KILL the engine in gear.It should stop immediately and not diesel.

 

^^^^^ that's it..

 

If it is the fan you can either hook up a relay or a diode in line to stop the back feeding.

 

I'm a big believer in relays, I operate almost everything with them, they eliminate a lot of electrical gremlins.

 

I'm glad to learn I'm not the only one who does that! Every time I drive my daily driver, I shut it off in gear and hold the brake as I let out the clutch. It's a quick and effective solution for an engine that keeps running after shutting off the key. Something I read years ago convinced me that my car does it because I have the timing advanced for the altitude. Now I wanna go retard the timing and see if it stops when the key goes off.

 

The Painless instructions talked about a diode in line if the key won't shut off motor, but not for one wire alternator, where would you install it on the hot to fan?

 

Check the timing.

 

Did check, it was ok , I just changed it a degree. With it doing the delayed couple second shut down, just when the car has been run for awhile and hot and not cold I think what some are saying about the fan relay or diode may fix it.

 

How is the fan wired up now, any kind of controller? If it only comes on when actually warmed up it makes me think it already has a relay or controller which should eliminate the run on issue (from fan) but need to know how it's hooked up.

 

The fan is wired with fused 10 gauge wire from keyed power side of fuse panel to a adjustable temperature control box with probe that sticks into radiator core to sense temperature. Then power from adjustable control box to fan. That's what the instructions showed.

 

Reading the instructions doesn't sound like there is a relay in this set up

 

You're right no relay in that system. As it's wired now you probably need a relay, it could be back feeding through the controller. One thing you could try if not a pain would be switching your power source to the accessory side of the ignition switch (if you have one). That should break the the back feed to the ignition circuit when you shut key off.

 

You mean power source for fan?

 

Couple thoughts, what about diode in wire from control box to fuse panel? or would it be any different if changed 10 gauge wire from controller to Constance power side of fuse panel instead of keyed side?

 

Yes, I'm assuming it's the car in your avatar and didn't know if you were using the original ignition switch which I didn't think had an accessory position.