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By Rono - 7 Years Ago
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I'm trying to figure out why my 56 Customline has developed a run on problem after I turn the key off. I do have a new MSD Street Fire ignition box, but I don't think that is the cause. I double checked spark timing today with the engine warmed up and the vacuum from the distributor plugged and I am right at 12 degrees BTDC with engine idle at 800 RPM. The car runs fine at all speeds and the spark plugs look like they are burning fine. Any ideas?
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By miker - 7 Years Ago
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Ron, does it just keep running, or is it the “rattle shake diesel “ problem the early emission cars had?
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By Sandbird - 7 Years Ago
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You might want to read this on the MSD web page. Follow this link and click on the engine run on tab. https://www.msdperformance.com/support/troubleshooting_techniques/
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By Rono - 7 Years Ago
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Mike;
It's the rattle/shake and then it quits. I will take a look at the MSD link for run on issues.
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By Rono - 7 Years Ago
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After checking out the MSD Troubleshooting link for "run on" issues, they indicate those problems to be linked to external regulators causing a small amount of current to back feed into the ignition circuit. Since I am running 1 wire alternator with no external regulator, I guess this isn't the problem.
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By Gene Purser - 7 Years Ago
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Electric fans hooked up without a relay can backfeed the ignition.
Carbon in the cylinders can cause "hot spots" and ignite fuel in the cylinder.
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By Rono - 7 Years Ago
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Thanks Guys! I do have a "Cooling Components" electric fan, but it does have a relay. It is not however thermostat controlled. I have it hooked up to a toggle switch which gets power from the battery side of the ignition switch. It's also possible thatI have been running on the rich side which could cause the carbon buildup in the cylinders. Maybe I need to take it out tonight and get on it a bit!
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By FORD DEARBORN - 7 Years Ago
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Is the tack driven by the new MSD box? Could the tack be off enough to indicate 800RPM at idle when the engine may be idling at 900? The slower the idle RPM the less chance of engine run-on after shut down. Hope this helps, JEFF.......................
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By Rono - 7 Years Ago
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Jeff;
Yes, the MSD box is connected to the tach. I have been having a problem with erratic idle and loosing spark at low RPM which is why I changed out the 10 year old MSD box with this new MSD Street Fire box which is supposed to provide good spark at low RPM. Before, I had to set the idle at 1,000 RPM or it would almost stall when I came to a stop. Even now it is not always steady at 800 RPM and and sometimes drops to 300-400 RPM. I'm wondering if it may be somehow vacuum related.
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By miker - 7 Years Ago
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I didn’t think it would be carbon build up with you driving.😄. For intermittent vacuum leak returning to idle, how old is the carb? Maybe the throttle shaft? I’ve seen that even on new carbs.
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By Ted - 7 Years Ago
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My vote is on the rotating fan is generating a current when the key is turned off. You could potentially test this by making sure the fan is not turning when you turn off the ignition and see if the engine ‘run on’ problem goes away.
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By Rono - 7 Years Ago
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Ted;
That is a good idea. I test that theory out today.
Thanks everyone!
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