Hey guys, I have an 86 Trans am 305TPI. Ive had this issue for a couple years but thought I had it fixed until now. when I turn the ignition off and remove the key, the car keeps running and doesn't skip a beat.

this started happening in 2014 after i had an overheating issues where it would creep up to around 240 degrees so i figured it was dieseling. I replaced the cooling system and the issue hasn't happened until today. I haven't driven the car in about 7-8 months and decided to replace the fuel injectors and rebuild the fuel pressure regulator.

Today I cranked it over for the first time after completing the job and it started after I jumped the battery. I went to shut it off and it kept on running. the car was only running for 2 minutes max before I went to turn it off. I had to pull the 20 amp fuel pump inline fuse by the battery to get it to stop running.

Should I go ahead and replace the ignition switch to rule that out? the only possible cause I can think of is that in 2014 I got in a fight over the phone while sitting in my car and while I was enraged I started punching the steering wheel which bent the steering wheel and resulted in the turn signals to not shut off by themselves when completing a turn. I'm sorry in advance for physically abusing my thirdgen, it didn't deserve it

 

Next time it does that, try unplugging the small connector on the alternator.

If it stops, it's probably the alt.

If not, ... probably something else.

Running for 2 min shouldn't bother anything except maybe the driver's ego. That's repairable though, they make liquids that help greatly.

 

will give that a try tomorrow, thanks.

and didn't quite get the joke lol

 

Oh... you will, eventually. liquid ego. The yolk will be on you.

 

guessing it's an alcohol reference lol, you certainly have a way with words sofa

 

Hmmmm.... is alcohol a liquid?

{consults CRC chemical reference}

Some of them are.

Seriously though, if you turn the key off and the engine keeps running for 2 min, then power is getting to the ignition somehow... just gotta narrow the potential sources down. Since the "signal" part of the alt is on the same wire as ignition, it's a logical thing to try to confirm or eliminate right up front.

 

Well I think I found the issue. decided to go out to the garage and check for vacuum leaks since my idle was pretty high and sure enough I forgot to plug the brake booster vacuum line back into the plenum. Can't wait to start it up tomorrow and see.

 

 

Vacuum leak helped the idle but it still didn't turn off with the key. I pulled the 2wire plug on the alternator and it shut right off. Guessing I should go with a new alternator?

 

Probably so...

 

just tested the diodes with my multimeter via this method and it passed..

 

Wierd question, but if the motor is running without the key being on, doesnt that denote that the distributor is getting a 12v feed from somewhere. We clearly arent talking about run-on/dieseling - the bloody things actually running as per normal.

Go to the car, leave the key off - check the voltage on the wire heading to the distributor, if it has 12v then its probably getting it from somewhere that it shouldnt be

 

Yeah I know its getting 12 volts from somewhere, I assumed it was dieseling years ago when it first happened due to over heating but since its happening again it's definitely a wiring issue.

I just ordered a fan controller since the previous owner wired the fan to the ignition which could cause this.

 

the one thing that amazed me about these cars - might have changed it in later models - was the lack of relaying on circuitry in the car.

For example, the headlight switching overheating etc - solvable with a relay

Since owning this car ive installed a tonne of relays to do the heavy work, and tbh, without a relay in play, that could potentially be backfeeding your ignition circuit.

Does you starter motor utilize the constant power terminal (cant remember which one it is) that feeds the distributor while cranking? - has anyone done the ford starter solenoid conversion to the car etc>?

 

another idea might be to use a test light, attach it to that ignition feed

pull fuses one by one and see what shuts it off..

 

There is no "constant power ... while cranking". That's a bit like something that's white, except it's black. Either it has power constantly, or it has power while cranking: can't be both.

However that may be, the terminal that has power while cranking, is the "R" terminal. That was only used with points type distributors, i.e. pre-74. Not applicable to these cars regardless.

For whatever reason, the alt keeps alting, even when the key tries to tell it to stop. First thing to suspect is the alt itself. Then we have found that the key does everything else it's supposed to do... probably not a problem involving the key. I'd say it's "possible" for something about the car to do this but not very "probable". I'd stick with the more "probable" in terms of guesswork.

 

Will exchange my alternator at autozone tomorrow since it's under warranty. just gonna be hard to convince them since I don't think they test the diodes, just the voltage output. the alternator was replaced in early 2015 but it has seen many dead batteries since then.

 

logically there has to be power to the dist while cranking, or the engine wont fire until you stop cranking (usually stumble into life)

i had that issue not that long ago, had to connect power directly to my dist to get it home. Power was applied to the dist in the on position but not cranking. therefore wouldnt fire until you released the key (which was crap in cold weather). once the key is released it had 12v.

hence my statement, something has to provide power to the dist while cranking

 

The power to the dist comes from the ign sw; not related to the starter at all. Not related to cranking either, it has power in both Start & Run. And of course it's not "constant power" either, it's only powered when the key is on.

The problem you describe is a typical points car situation... something about the ign sw or its circuit is farkled, but the "R" terminal circuit still works. So you get the deal where you hit the key and it starts right up but then dies when you let the key go to Run. Again, not common in a 74-up vehicle.

 

nah fair call - mine has been molested by various owners over time

either way, some random circuit is powering this blokes distributor and its getting 12v in the off position - test light on the dist feed and pulling fuses will at least narrow it down.

if that constant 12v is only remaining when the car is off, that means there is a backfeed by something that is getting relayed power.

could be simple, could be hard - either way i dont envy this bloke

 

ordered a cs144 alternator and pigtail adapter, should have it tomorrow. figured if I need a new alternator I might as well put a good one in.

 

did you go fuse hunting or are you just throwing parts at it?

 

I've had plans to put a nicer sound system in the car so the alternator was more of a "kill two birds with one stone" kind of deal..

 

The car now shuts off when I turn key off with the new alternator but it still runs on for about 1 second after the key shuts off.

I swapped out the egr solenoid today and accidentally triggered a check engine light so when I went to check the code, the light wouldn't flash which leads me to believe that a lot of my issues are coming from the prom that I bought from tpiparts.com to remove the cold start injector and change to the later style of dumping more fuel into the other injectors on start up. Gonna put my old prom in tomorrow and see how it runs.