i took the Z28 out to go on a short errand today and i noticed her latest problem...now when i turn the key off, it takes an additional 3 seconds or so for the motor to actually turn off...ideas, input?

Josh

 

It's called dieseling. Back in the 70's when gas went from 100 octane to the 80's, high compression motors would continue to run-on because the compression was high enough to keep igniting the gas - even without a spark from the plug.

My first guess would be that you got some real bad gas. Try getting rid of it and put in some high octane to see if that fixes it.

If not, what the car makers did in the 70's is to install a seleniod that keeps the car's throttle plates open at idle, but when you shut off the motor the selenoid allows the throttle plates to close shut.

I'm no expert on your car, but if it has a seleniod like this, it may be stuck open.

I hope this helps you out.

 

no, this aint dieseling. i mean, for three seconds, it KEEPS running. it is like i didnt even turn the key off for about 3 seconds...damnedest thing i have ever seen

Josh

 

You have a mechanical fuel pump, right?

 

yea, actually, i have BOTH. an electric pump to prime the carb, and a mechanical fuel pump for when the motor is running...pretty dumb if you ask me. actually, my mechanical one is on the fritz right now. at higher RPM's, it runs out of gas, but i cant afford one until payday...

Josh

 

Is the electrical pump powered through a factory relay? if so, I'd say the relay is sticking.

 

yea, ya know, that could be a possibility. it is a FACTORY pump, so it has a FACTORY relay...but to the best of my knowledge, it should only be running during initial ignition turn-on and startup...the rest of the time it should be ALL mechanical pump...and besides, i am pretty sure that the ignition being turned off is suppose to kill IGNITION to the motor, and that being the case, i dont care if fuel is getting to it or not, it will still promptly die due to no ignition...that is just what i think, i could very well be wrong....thank you so much for the help anyhow...i will check the relay, if i can ever find it

Josh

 

AFAIK, the dual pump thing cam in 87 to address the vapor lock issue, meaning it SHOULD be running during vehicle operation. however, if a person complained to a dealer about it, it was available as an upgrade. And since it is a factory thing, you should have a relay. Look on the firewall, driver side for it. You can also pull the fuel pump relay fuse, which would be located up by the battery and coolant puke tank, should be bolted to the firewall, small inline fuse, 20a. Or, you can pull the fuel pump fuse from the fuse box. Disconnecting any of those 3 will effectivly kill the pump. Try doing that next time this happens.

 

Check/clean the grounding of your steering column and examine the ignition module to see if any wires are brittle/cracking. Sounds as though its not grounding out the ignition very well.

 

Do you have an aftermarket ignition system? If so that could be where the problem is.
I have a Jacobs system that ran wonderful forever after you turned the key off. Turned out they knew about this possible problem and shipped me a capacitor (or diode, I can't remember) to fix the problem.

 

nope, my Z is all stock down to the air filter as of now...the only "mod" is the aftermarket CD player...

Josh

 

never mind, brain fart, lol...