1972 F-750 with points...and Duraspark??
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Freshman User
Joined: Oct 2013
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From: San Diego, CA
1972 F-750 with points...and Duraspark??
I recently acquired a super clean, super low mile '72 F-750 with a 391FT and a points-type distributor. Most definitely has points - no question about it.
After removing a bunch of residual fire pumper electrical systems, I developed a starting problem. Upon tracking it down, I discovered some kind of ignition box immediately adjacent to the glove box, on tne right, under the dash - it's clearly a factory part and install.
Is this some weird pre-Duraspark I system? And most importantly, does anyone know if hall effect or optical sensors can replace the points on this system?
upon tracking down
After removing a bunch of residual fire pumper electrical systems, I developed a starting problem. Upon tracking it down, I discovered some kind of ignition box immediately adjacent to the glove box, on tne right, under the dash - it's clearly a factory part and install.
Is this some weird pre-Duraspark I system? And most importantly, does anyone know if hall effect or optical sensors can replace the points on this system?
upon tracking down
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Freshman User
Joined: Oct 2013
Posts: 27
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From: San Diego, CA
Apparently, it's "..permatuned transistor ignition.."
Since I haven't been able to find answers elsewhere, I just bought a set of original '72 shop manuals. In section 23-01-3 of the Engine book, it describes, "The permatuned transistor ignition system...on the 361, 391 [bingo], 401, 477 and 534 V8 engines."
It goes on to say that the coil in this system is designed to draw 12 amps peak, and about 5.5 amps average current. It says that the transistor in the system --- the silver box I found under the dash near the glovebox -- is basically a solid-state relay connected between the battery and the coil. The points simply trigger the transistor, and the transistor ultimately is what provides current to the coil. *Both* connections to transistor (from the ignition switch to the transistor, and from the transistor to the coil) have a resistor in line. Hence the strange double/two resistor setup on the passenger-side fender.
What I still don't know is whether the "permatune transistor" box will behave correctly when it sees a signal from a hall effect sensor (e.g. Accel Points Eliminator).
Anyone know? A definitive answer sure would be appreciated before I go spend the money to buy one...and test. The great thing about forums like these is that we can get expert knowledge...before spending money on tests.
Any shared personal experience with this would sure be appreciated.
It goes on to say that the coil in this system is designed to draw 12 amps peak, and about 5.5 amps average current. It says that the transistor in the system --- the silver box I found under the dash near the glovebox -- is basically a solid-state relay connected between the battery and the coil. The points simply trigger the transistor, and the transistor ultimately is what provides current to the coil. *Both* connections to transistor (from the ignition switch to the transistor, and from the transistor to the coil) have a resistor in line. Hence the strange double/two resistor setup on the passenger-side fender.
What I still don't know is whether the "permatune transistor" box will behave correctly when it sees a signal from a hall effect sensor (e.g. Accel Points Eliminator).
Anyone know? A definitive answer sure would be appreciated before I go spend the money to buy one...and test. The great thing about forums like these is that we can get expert knowledge...before spending money on tests.
Any shared personal experience with this would sure be appreciated.
Fleet Mechanic
Joined: May 2005
Posts: 1,575
Likes: 11
From: Puyallup, WA
It was common practice in the early days of transistorized ignitions from many manufactures to use points as a trigger. The lower amperage / voltage across the points made them last a lot longer, but on the flip side they got dirty fast from oil vapors and without enough amperage the points could not self clean. This is what ultimately doomed the systems to a early demise.
The practice was pretty much ended by around 1973 or so. Not sure if it will work with a hall effect or not. All manufactures changed there "transistorized brain boxes" when moving away from a points triggered system. Perhaps that is the telling thing?
David
The practice was pretty much ended by around 1973 or so. Not sure if it will work with a hall effect or not. All manufactures changed there "transistorized brain boxes" when moving away from a points triggered system. Perhaps that is the telling thing?
David
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Freshman User
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From: San Diego, CA
I'm going to go ahead and just try it. It appears the difference in question here is a small non-zero voltage when the hall effect sensor is in "open circuit" mode. Page 4 of this doc [I love Google] explains it (Common Mode Voltage) quite clearly:
http://sensing.honeywell.com/index.php?ci_id=47847
So... the question I'll put to rest through testing i.e., installing the damn Accel Points Eliminator... is whether a tiny non-zero voltage will be interpreted as "points are open" by the Ford Permatune IGBT box.
I'll test it and post results.
http://sensing.honeywell.com/index.php?ci_id=47847
So... the question I'll put to rest through testing i.e., installing the damn Accel Points Eliminator... is whether a tiny non-zero voltage will be interpreted as "points are open" by the Ford Permatune IGBT box.
I'll test it and post results.
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
If you are putting a points eliminator in it, why not just put a stock points type coil in it and just run it that way. Eliminate all that stuff.
Or leave it there and the wiring and use it "for show", but not go.
Or leave it there and the wiring and use it "for show", but not go.
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