Demons possess my '69 Mustang

[solidJ 11]

1969 Mustang coupe, 6cyl-200, automatic, no air, Pertronix ignition, high performance wires and coil.  Yesterday it stalled at a red light after driving 2 blocks.  I placed floor shifter to neutral and it started right up, then engine started racing at very high speed.  Strangely enough, when I shifted into Drive, the car went slowly so that I could pull off into a parking lot.  I shut off the ignition, and the high speed engine revving continued!  I checked the accelerator cable and it wasn't stuck.  Car continued to rev higher than before.  I removed the air cleaner and cupped my hand tightly over the carb throat, with no effect whatsover.  This all took place, about 5 minutes, with the ignition key off.  I returned to the car and turned the key to "on" and the revving stopped and all was normal.  I drove about 20 miles in-town driving, and later 20 miles back home with no further problems.  Of course my mechanic is stumped.  Today I drove a few miles with no further problems. Any ideas of the problem?

[barnett468 418]

choke may have stuck or throttle plate rod pivot hole in carb base may be worn not allowing it to return to idle. if it happens again try forcing the throttle closed, disconnect the distributor cacuum hose, make sure the choke high idle can is not engaged.

 

[RPM 1,190]

Your 69 must be related to a 65 coupe 6 cyl I once owned. After work one day it died after warming it up. Cranked it without it starting till the battery wouldn't crank it. Got a ride home to get tools and jumper cables. When we returned to the car I asked my brother if he heard that sound. The car was running, in park, with the ignition off and the keys in my pocket. True story.

[barnett468 418]

59 minutes ago, RPM said:

After work one day it died after warming it up.

I had the exact same problem with my last date.

[Caseyrhe 650]

To much golf can cause that too

[RPM 1,190]

I have never experienced too much golf. 

[newstang 388]

have a test light ready when it happens again, obviously with the key off its still getting power at the coil. 

so could be bad ignition switch or power is feeding back from elsewhere.

 

 

[JayEstes 172]

That’s kind of terrifying.  Surprised you would shift it into drive while the engine was revving.  I’d also worry about blowing the engine if it’s wide open and won’t stop.

next time to kill the engine I would pull the main coil wire.  It’s easy and quick and should put an end to high speed revving.

ive had at least one incident where my car failed to start and I cranked until batt died.  I charged battery and haven’t had a problem since.  My suspicion for your prob is same as mine-  flaky pertronix.  I can’t prove it, but I wonder.  Something is keeping power flowing with key off- could that be a sticky solenoid?  Even though key off- it’s still engaged?  Idk. Very weird.

[mwye0627 44]

Still it should be pretty easy to diagnose and fix on these older cars, since there are only a few things that could possibly go wrong...

I was at my buddies body shop on Monday when a customer came in with a 2016 Jeep Patriot looking for an estimate on a bumper repair.   He shut the car off and removed the key from the ignition. Suddenly the engine started cranking over all by itself!!!

I had my buddy put the key back in the ignition and turn it to the ON position and the engine quit cranking.   I remembered from work that several years ago (I believe it was around 2007) many U.S. automakers started having the PCM control the cranking function.  The manufacturers and EPA had found that on startup, if the vehicle did not have high enough fuel pressure it would create a "Lean Start" condition which results in excessively high NOX emissions....   To solve that problem they put the PCM in charge of the Cranking Circuit.   When the key was moved to the Crank Position, the PCM would first verify that the fuel pressure was high enough, and then it would make a relay contact which would allow the starter to crank the engine.

I have had many instances over the past 10 to 15 years where the vehicle I was operating exhibited very strange and abnormal operation that would only be corrected by pulling over, turning the vehicle off and then back on, effectively Re-Booting the on-board computers.   This is what I assumed was happening with this Jeep...

And now the manufacturers think that Autonomous vehicles are the answer, when they can't even make current technology work properly???

Hmmm....

[danno 128]

I  am trying to imagine how the 2 issues could be connected.  Issue 1 is revving high, and issue 2 is running with the key off.   The only possibility is the wire from the starter solenoid to the ignition coil. In the system there is a separate wire to supply 12 volts to the coil when  the key is in the start position.  When the key is in the RUN position, the coil gets about 9 volts because of the resistor wire.   If this wire is shorted to 12 volts (maybe in the starter solenoid), it would supply 12 volts to the coil if the ignition is off or on.    Giving the coil 12 volts instead of 9 volts could provide a larger spark, and if the carb mixture is rich, it could run faster with a stronger spark.

If this is not it, you must coincidently have 2 separate issues occurring at the same time.

 

[Guillaume69 150]

I had the « engine still running with key in my pocket » freaky voodoo type stuff, a couple years ago.

Turned out it was a bad solenoid.

No high revs issue, though.

[Midlife 814]

A sticking solenoid would do the engine run-on, but usually the starter motor would also be engaged.  High revving may be caused by a bad motor mount that caused the accelerator linkage to stick or get jammed somehow. 

[RPM 1,190]

2 hours ago, Midlife said:

High revving may be caused by a bad motor mount that caused the accelerator linkage to stick or get jammed somehow. 

Ah, memory lane. My 6 cyl did that often.

[Guillaume69 150]

6 hours ago, Midlife said:

A sticking solenoid would do the engine run-on, but usually the starter motor would also be engaged.  High revving may be caused by a bad motor mount that caused the accelerator linkage to stick or get jammed somehow. 

Well, Randy, in my case, the issue appeared at engine shut off, after normal driving. No starter still engaged or something of that nature. Just parking the car in the garage, turning the key into the off position, removing it from the ignition switch, and engine still running...

You find yourself standing next to your car, looking at your keys in your hand, wondering if you’re in a movie called “Christine vs Poltergeist”. All I had to do then was pop the hood up and unplug the brown (iirc) wire from the solenoid  to stop this paranormal phenomenon.

That stuff bugged me (haunted me?) on and off for 3 or 4 months until I decided to swap the solenoid (which was a brand new one from Scott Brake, btw)...

Never happened again after I put a new fonctional solenoid. I am glad it worked because my next - and last - option would have been to bring in Father Karras for an exorcism...

G

[aslanefe 333]

If your ignition switch is bad, the engine may not shut off when you remove the key (switch still sending power to coil) but starter may not be running. If the starter selonoid is sticking, starter will stay engaged and running.

[Guillaume69 150]

I swear that in my case, ignition switch was good (first thing I tested) and solenoid was dead.

Starter never stay engaged. Only symptom was unable to switch the engine off with key, every now and then.

These are facts. I can’t explain it, but facts still.

[ray1970 88]

I have had two bad solenoids that would not let my motor shut off.

it can happen..

 

As far as the revving goes I can only think the ing adv froze open. vac. or mech.

You My want to look at that..

[solidJ 11]

9 hours ago, ray1970 said:

I

 

As far as the revving goes I can only think the ing adv froze open. vac. or mech.

You My want to look at that..

"ing adv froze open".  Could someone please explain this?

[barnett468 418]

2 hours ago, solidJ said:

"ing adv froze open".  Could someone please explain this?

ummm...i think he meant to say that maybe your vacuum advance or mechanical advance stuck slightly open temporarily to cuse the temporary high idle.

[ray1970 88]

I was really thinking more than slightly open.

I forget at times not everybody gets that deep into what I think is simple when it comes to engines.

 

The adv. weights inside the dis. can bind up from rust over time and one or two other things     I have seen springs fall off also that control the return of the weights.   screws to long 

or something just bent from past repairs.. 

this can hold the Ing...adv.    beyond its normal setting that can make the motor surge or just rev high at times..

I am not really good at this explaining stuff...

 

On the very far end of this I have seen motors rev out of control with no plug wire on the plug...this will really screw with your mind!!!!!!!!!

 

 

 

 

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