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Run on with MSD?

  • Thread starter Thread starter 79 Fox
  • Start date Start date Jun 20, 2019

79 Fox

Active Member
May 21, 2019
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A van down by the river
Jun 20, 2019
#1
  • Jun 20, 2019
  • #1
Anyone with a 79-85 install MSD and experience run-on? If so, where did you put a diode?
 

FastDriver

I was uncomfortably high & wearing a helmet
SN Certified Technician
Sep 5, 2001
6,115
2,726
224
Vass, NC
Jun 20, 2019
#2
  • Jun 20, 2019
  • #2
What's run-on? Dieseling? I've run an MSD on most of my cars and haven't had the problems that others have, except with their TFI module.
 

79 Fox

Active Member
May 21, 2019
141
14
28
A van down by the river
Jun 20, 2019
#3
  • Jun 20, 2019
  • #3
The engine runs on because a small amount of current can leak back to the box which keeps things running. A diode in a certain place stops this flow, but we don’t know where it goes, and information is nowhere to be found.
 

RangerJoe

I leave the horn on while driving
15 Year Member
Apr 26, 2010
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Georgia
Jun 20, 2019
#4
  • Jun 20, 2019
  • #4
79 Fox said:
The engine runs on because a small amount of current can leak back to the box which keeps things running. A diode in a certain place stops this flow, but we don’t know where it goes, and information is nowhere to be found.
Click to expand...

Never heard of that before, but if current is flowing back into the box I would assume you would place it in the 12v power wire.

Joe
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
27,967
10,606
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polk county florida
Jun 20, 2019
#5
  • Jun 20, 2019
  • #5
There is a diode on the ground wire on the belt driven hydraulic pump on the dump truck, the manufacturer found that on some installations power was feeding back through the ground and the clutch would engage with the power switch in the off position. This may be the problem you have although I've never heard of the msd box causing an engine to 'run on'.
 

79 Fox

Active Member
May 21, 2019
141
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28
A van down by the river
Jun 21, 2019
#6
  • Jun 21, 2019
  • #6
Thank you guys so much!
 
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