68 911L "Run On"

[jfd]

How to stop Run On in my 68 911L with MSD and 6AL ignition system? Any help is appreciated?

[Haasman]

I suggest being a little more descriptive .... when I hear "run on" I think regardless of key position the motor continues running. That the engine is getting spark and fuel despite these systems being turned off.

[Bill Meyer]

"Run on" generally means dieseling, so I'd assume that's what he's asking. Usually built up carbon deposits cause this, so maybe it's been running really rich for some time?

[jfd]

Thanks guys
The car runs fine.
the key will not turn the engine off.
MSD defines this as "run on" and they have solutions for GM and Ford but not Porsche. They use a diode in line but do not recommend that fix for Porsche. I have the same setup on my 75S with no problem.???
Appreciate your help

[62S-R-S]

..the key will not turn the engine off.
MSD defines this as "run on" and they have solutions for GM and Ford but not Porsche. They use a diode in line but do not recommend that fix for Porsche. I have the same setup on my 75S with no problem.???
Appreciate your help

Wondering what rpm's you're seeing before shutdown? One engine really went full tilt with this problem recently, and my sense is that fuel and corn contribute more than carbon does. Can you, with mfi drop your idle speed to 650 - 700 -- you may find the issue does not occur at that speed.

[jeff eelkema]

I assume you are running carbs so nothing to shut off fuel supply, turning off ignition only cuts the spark so you have fuel and a source of ignition. Typically caused by carbon or overheated tip of spark plug. Lean mixtures and or retarded timing will cause super high combustion temps resulting in hot spots that cause the run on. Too high idle speed adds to the problem.

[Bill Meyer]

Thanks guys
The car runs fine.
the key will not turn the engine off.
MSD defines this as "run on" and they have solutions for GM and Ford but not Porsche. They use a diode in line but do not recommend that fix for Porsche. I have the same setup on my 75S with no problem.???
Appreciate your help

The car running fine has nothing to do with "run on" after turning the key off. We're still talking about two completely different things here, so can't really help if you don't give more detail. As I said above, typical "run on" is defined by a motor continuing to ignite fuel even when the spark from the ignition system has been turned off, or dieseling as it's otherwise known. You seem to be saying the car continues to run as normal when turning it off, as in the ignition is still firing and you could continue driving with the key in the off position? That would be really odd (and how do you actually get it to stop??) but would simply indicate the ignition switch is simply not killing power to your ignition system.

[jmz]

You are getting feedback somewhere. A diode could fix it. Check and see if feedback it is coming from the alternator warning light.

[jmz]

The car running fine has nothing to do with "run on" after turning the key off. We're still talking about two completely different things here, so can't really help if you don't give more detail. As I said above, typical "run on" is defined by a motor continuing to ignite fuel even when the spark from the ignition system has been turned off, or dieseling as it's otherwise known. You seem to be saying the car continues to run as normal when turning it off, as in the ignition is still firing and you could continue driving with the key in the off position? That would be really odd (and how do you actually get it to stop??) but would simply indicate the ignition switch is simply not killing power to your ignition system.

I think he's just calling it "run on" I read what he wrote and it sounds like he is simply saying his ignition switch will not kill the engine.