HEI distributer issue
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5th Gear
Joined: Oct 2020
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HEI distributer issue
I've had an HEI distributor in my 79 f250 for several years without issues. The engine is a 300 cubic inch out of a 74 f350. My question is, when I test the wire from the ignition switch to the distributor in the ON position it shows 12.4 volts. If I test it in the START position and it doesn't show 12 volts, is my ignition switch faulty? Thank you.
FTE Legend
Joined: Nov 2015
Posts: 30,915
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From: Angier, NC
Welcome to FTE
I would say no the switch is not at fault.
You did not post what this cranking voltage is and I am guessing you are testing at the dist. power in wire?
Why would you now test this when it has been running good for some time? What are you trying to trouble shoot?
Why would you do away with the DSII the truck came with to install the HEI when both do the same thing with the same out come?
On the mid 80's trucks I can see with the feed back system and computer controlled timing that may be locked if a sensor is bad but your truck did not have that.
Ok with that out of the way here is why I say not at fault and you can test this at other places in the electrical system.
When cranking the starter draws a LOT of power and this will lower the voltage seen in the system.
I dont know if you would see a big drop at the battery like at the dist. because the voltage has to go from battery into the switch and out to the dist. thru all that old wiring but you should see a drop at the battery also.
If you have one of them voltage checkers that plugs into the cig lighter you will see it drop there.
So what are you trying to fix?
Dave ----
I would say no the switch is not at fault.
You did not post what this cranking voltage is and I am guessing you are testing at the dist. power in wire?
Why would you now test this when it has been running good for some time? What are you trying to trouble shoot?
Why would you do away with the DSII the truck came with to install the HEI when both do the same thing with the same out come?
On the mid 80's trucks I can see with the feed back system and computer controlled timing that may be locked if a sensor is bad but your truck did not have that.
Ok with that out of the way here is why I say not at fault and you can test this at other places in the electrical system.
When cranking the starter draws a LOT of power and this will lower the voltage seen in the system.
I dont know if you would see a big drop at the battery like at the dist. because the voltage has to go from battery into the switch and out to the dist. thru all that old wiring but you should see a drop at the battery also.
If you have one of them voltage checkers that plugs into the cig lighter you will see it drop there.
So what are you trying to fix?
Dave ----
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5th Gear
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Sorry for not being clearer about everything. I replaced the 351m with the 300 and the 300 had the HEI already on it. I figured I'd just use it and do away with the external coil and the ignition module.
The issue I have now is it isn't firing. I was told that if I hooked a continuity tester to the battery and touched the C contact on the module and turned the engine over the light would blink. They said that shows the pickup and the module was working right. It blinked so I replaced the coil and rotor cap. I tested the wire from the ignition switch to the distributor when in the ON position and it showed over 12 volts. To me, that eliminated the wire being bad. I'm not a mechanic but I've had these old Fords most of my life and have usually been able to keep them running. This is my first HEI and I don't know much about them.
The issue I have now is it isn't firing. I was told that if I hooked a continuity tester to the battery and touched the C contact on the module and turned the engine over the light would blink. They said that shows the pickup and the module was working right. It blinked so I replaced the coil and rotor cap. I tested the wire from the ignition switch to the distributor when in the ON position and it showed over 12 volts. To me, that eliminated the wire being bad. I'm not a mechanic but I've had these old Fords most of my life and have usually been able to keep them running. This is my first HEI and I don't know much about them.
FTE Legend
Joined: Nov 2015
Posts: 30,915
Likes: 4,123
From: Angier, NC
Ok I got it and I would most likely do the same, keep the HEI if that was what came with the motor.
The HEI should only need 1 wire to power it and as a test run a wire from the battery POS+ to the power in of the HEI unit and see if it will run then.
If it still does not have spark then there is something wrong with the HEI unit in my book and would need more looking into why no spark.
What wire are you using to power the HEI unit?
They say you can use one of the wires from the DSII to power HEI's but I dont know what color wire it is and this is on the 80 - 86 trucks so may be different on yours?
I dont know if I would be using a continuity tester. I think a good old test light, not the new LED ones, would be better to check with.
Old tools for testing on old cars & trucks.
Dave ----
The HEI should only need 1 wire to power it and as a test run a wire from the battery POS+ to the power in of the HEI unit and see if it will run then.
If it still does not have spark then there is something wrong with the HEI unit in my book and would need more looking into why no spark.
What wire are you using to power the HEI unit?
They say you can use one of the wires from the DSII to power HEI's but I dont know what color wire it is and this is on the 80 - 86 trucks so may be different on yours?
I dont know if I would be using a continuity tester. I think a good old test light, not the new LED ones, would be better to check with.
Old tools for testing on old cars & trucks.
Dave ----
Tuned
Joined: Jun 2018
Posts: 458
Likes: 123
From: Arkansas
There's one wire that comes from the DSII to the coil that is a resistor wire(red/green?) that is what powers the coil while running, it reduces the voltage down to like 6 volts? Try putting a multimeter on the wire you're using for your coil and turning the key on, see if the voltage slowly drops with the key in the run position. If it does then you need to find another source that has 12 volts all the time. The stock wiring gives the coil 12 volts for starting and then switches to the resistor wire in the run position. I know I went back and forth a few times finding the right one to use for my 1 wire distributor.
Having said all of that, I doubt it's the issue if it just started causing trouble. I've never used an HEI but another thing I just thought of is: what is the resistance of your coil? I know for my summit distributor with an internal module the manual says not to use a coil with more than 1.0 ohms of resistance or you WILL damage the module. A quick google search brought up to use a low resistance coil with HEI as well.
Having said all of that, I doubt it's the issue if it just started causing trouble. I've never used an HEI but another thing I just thought of is: what is the resistance of your coil? I know for my summit distributor with an internal module the manual says not to use a coil with more than 1.0 ohms of resistance or you WILL damage the module. A quick google search brought up to use a low resistance coil with HEI as well.
FTE Legend
Joined: Nov 2015
Posts: 30,915
Likes: 4,123
From: Angier, NC
There's one wire that comes from the DSII to the coil that is a resistor wire(red/green?) that is what powers the coil while running, it reduces the voltage down to like 6 volts? Try putting a multimeter on the wire you're using for your coil and turning the key on, see if the voltage slowly drops with the key in the run position. If it does then you need to find another source that has 12 volts all the time. The stock wiring gives the coil 12 volts for starting and then switches to the resistor wire in the run position. I know I went back and forth a few times finding the right one to use for my 1 wire distributor.
Having said all of that, I doubt it's the issue if it just started causing trouble. I've never used an HEI but another thing I just thought of is: what is the resistance of your coil? I know for my summit distributor with an internal module the manual says not to use a coil with more than 1.0 ohms of resistance or you WILL damage the module. A quick google search brought up to use a low resistance coil with HEI as well.
Having said all of that, I doubt it's the issue if it just started causing trouble. I've never used an HEI but another thing I just thought of is: what is the resistance of your coil? I know for my summit distributor with an internal module the manual says not to use a coil with more than 1.0 ohms of resistance or you WILL damage the module. A quick google search brought up to use a low resistance coil with HEI as well.
HEI has the coil built into the dist.
Only the early HEI for the 250 six did it have a coil not part of the dist. but any of the aftermarket HEI's for a Ford 300 six the coil is part of the dist.
Yes that wire may drop voltage but have seen in posts it will work for the HEI on the 300 motors in the 80's trucks.
Now part of the problem on finding a different power wire is it has to have power both when cranking and running. It is hard to find 1 wire that does both.
What has also been said is to use that wire to trigger a relay that then powers the HEI dist.
Again I would run a test wire from battery to dist. to see if it will have spark then.
Dave ----
Tuned
Joined: Jun 2018
Posts: 458
Likes: 123
From: Arkansas
Damn, dunce moment. I think I knew that, just never used an HEI
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5th Gear
Joined: Oct 2020
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I ran a wire from the POS+ on the battery to the BAT lead on the distributor but still nothing. I'm not sure what size the wire is that runs from the ignition switch to the distributor. It's worked for several years. The tester I used looks like a screwdriver with a light in the handle. That's all I have for now. Thanks Dave and beardedcap.
Last edited by T.Oiler; Jan 2, 2024 at 09:17 AM.
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Lead Driver
Joined: Nov 2006
Posts: 5,217
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From: Pa.
On your starter relay mounted on the firewall you'll see an "I" and "S" connector on the face towards the motor. The "I" should read 7-8 volts in the run position on your ignition switch. The "S" should read 12+ volts at start. At the coil you should have the same readings. This was engineered this way to save wear on the ignition system while running because a full 12 volts is way overkill for the ignition ststem while running. The 7-8 volts at the coil by running a ballast resistor in-line to reduce the voltage and that wire is pink in color usually. Your HEI system takes a full 12 volts so any ballast resistor in line is not going to be of any use in the HEI system. When the HEI was installed they should have by passed the ballast resistor. Do you have a factory ammeter in your dash ?
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5th Gear
Joined: Oct 2020
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Well, A buddy of mine had an HEI for my 300. Replaced it and fired up the first try. I assume that it was the module or the pickup that was bad. I'm going to have it tested. Thank you all for your help.
Cargo Master
Joined: Mar 2008
Posts: 2,569
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From: Washington
On your starter relay mounted on the firewall you'll see an "I" and "S" connector on the face towards the motor. The "I" should read 7-8 volts in the run position on your ignition switch. The "S" should read 12+ volts at start. At the coil you should have the same readings. This was engineered this way to save wear on the ignition system while running because a full 12 volts is way overkill for the ignition ststem while running. The 7-8 volts at the coil by running a ballast resistor in-line to reduce the voltage and that wire is pink in color usually. Your HEI system takes a full 12 volts so any ballast resistor in line is not going to be of any use in the HEI system. When the HEI was installed they should have by passed the ballast resistor. Do you have a factory ammeter in your dash ?
The GM ignition module doesn't have current flow with the key in the ON position. Which changes all the troubleshooting. No current flow means no voltage drop across the resistor wire.
Glad you got it fixed and running, just posting to help others in the future reading this post.
Jim
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