# F100 Ignition Issues



## MELOC (Sep 26, 2005)

this is revisited from an earlier post. i've been battling my 1981 F100 6 cylinder 300 ci. for a little while now. i don't seem to be getting enough fire. the last time i had someone help me check it out, he said he saw some fire but it didn't look like much. i've replaced the coil with a new one, but one that sat as a spare in the shed for a year or two. i replaced the distributor with a new one. i replaced the module on the driver's side fender well with a new one, but it is now about a year old. i'm running out of things to check, lol. the wiring harness isn't great, but if i am getting some fire you would think the wiring harness and the plugs that plug into the module and the distributor would be ok. in my mind, the wiring harness is either working or it is not.

anyone have any ideas?

also, what is the electronic device mounted on the passenger's side next to the battery and the solenoid? it is behind a rubber shield.


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## HermitJohn (May 10, 2002)

I've converted to vacuum advance Ford duraspark II distributor in both my F250 and Ranger. With this distributor, I use 70s era 4 terminal GM ignition module mounted on an aluminum plate (heat sink) external to distributor and a TFI coil from 80s Ford computerized system, TFI coil is nearly identical to the external HEI coil GM used on 4 and straight six engines in the 70s and you can use either though the Ford TFI coil is cheap and very abundant in any junkyard. The external HEI coil not so easy to find in junkyard. 70s era stuff just getting harder to find though you can buy a new aftermarket one if you are determined to use a GM coil. This is simple to wire up and totally independent from any screwedup/corroded Ford wiring harness, you just need a power source that is 12V hot when key is turned on. Using the GM module means you dont need any resistance wires like you do with the Ford module. Gives nice hot spark. My notion, this hybrid setup is way to go. Simple cheap and independent of Ford wiring harness except for finding 12V hot power source controlled by ignition switch. Works for me and you've never seen a more screwed up wiring harness than whats in my F250. Wonder the whole thing doesnt melt into one big puddle. I just wire around it when something quits that I actually need to work. I even wired in a 70s era GM alternator.

If you are absolutely determined to make the stock Ford system work, then problem is usually corrosion in some connection. Ford uses dialectric grease in its wiring connections and that dries out with age. The stock coil Ford used in the Duraspark II systems had terminals kinda hidden and corrosion is problem there though you say you replaced that. You can hotwire the Ford ignition module independent of the wiring harness also, just more complicated than using GM module. The Ford module needs the resistance in the circuit also.


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## HermitJohn (May 10, 2002)

Here is even simpler diagram:


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## HermitJohn (May 10, 2002)

Here is simple diagram of ignition using Ford Duraspark ignition module if you want to just wire around your wiring harness but use stock Ford parts:


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## MELOC (Sep 26, 2005)

thanks for the diagrams. the stock ford might be useful, but i get stymied with the use of resistor wire.


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## fordy (Sep 13, 2003)

...............Just to add to the excellent info from John , I redid a 1977 f250 and some of my electricial problems were caused by old ground connections . So , I took as many as I could find and used emery cloth on the metal body to remove rust and corrison and i added extra grounds as well . For instance , when I pushed the foot switch for brite lights , both head lights would go completely out . Bad ground as I remember . I often wish I had another old ford truck to work on but , they are a RAT HOLE for loose change and will consume vast quantities of time and money . My idea was to drop a Cummins 4 BTV (4 cylinder diesel) into a 3/4 ton . Others have done this and reportedly got 28 to 30 miles per gallon with a 3:54 to 1 axle ratio . Too much work for me , now , at my age and too much $$ required as well . , fordy:shrug:


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## HermitJohn (May 10, 2002)

MELOC said:


> thanks for the diagrams. the stock ford might be useful, but i get stymied with the use of resistor wire.


Ballast resistor or resistance wire is nothing new, 12V point ignitions used it to keep points from burning out quickly with the higher voltage. Point systems would start on full 12V then cut to the circuit with ballast to run, more like 9V if I remember. Figure out the resistance value of the wire and you most likely can find a ballast resistor with this value. Matter of fact I dont think there were all that much difference between ignition ballast resistors and you could probably say just buy one for a a 1967 whatever and it would work in the circuit but I dont know that for sure. Lot of info on web for various duraspark conversions for Fords and Jeeps as people hated those early computerized carbuetor systems. The Ford modules will burn out rather quick without the resistance in the circuit though. Thats why I prefer the GM module. I mean it doesnt get much simpler than that second diagram above. Two wires from distributor (the black wire from distributor is a ground) to one side of ignition module and two wires from other side of ignition module go to coil and one from coil to a switched 12V source. Even point systems are more complicated than that. 

You can use any 12V coil with the GM module, doesnt have to be HEI or TFI, even duraspark coil or a coil from a point system will work, just wont put out as high a voltage. And those TFI coils are only like $5 or $6 at junkyard. Around $25 to $30 new aftermarket. My Ranger came with a TFI coil and computer controlled carb and ignition that had to go. My old F250, I replaced a clapped out 460 that was in truck when I bought it with a 300 six that came with a duraspark distributor, didnt have a Ford ignition module since the 460 had points, but did have a GM ignition module and coil from a '75 Vega 4cyl in my junk box so used that and it worked well. The F250 was originally a diesel when it came from factory, so never was a duraspark ignition in the truck that I know of.


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## MELOC (Sep 26, 2005)

i've never been more dirt poor than i am right now. i have indeed found that rat hole, but i already have invested in a new fuel pump, module, distributor, rebuilt starter a battery and the coil i have had for a couple years that was new, but on the shelf in my shed when i installed it two months ago. the only other device i plan to buy is a single barrel carb as that is long overdue and a rebuild kit is out of the question in case that is suggested. i have been down that road once and it's a PITA with questionable results.

the resistor wire and ballast are indeed nothing new... the truck is a 1981. my concern with the resistor wire is not knowing exactly which wires are resistor wire, and how to control the length, and therefore resistence, of the wire. 

while i appreciate talk of customizing all of the systems on the truck, what i need to focus on is the most likely cause of limited spark. apparently the concensus is corroded wire, corroded resistor wire or terminals. if so, it would be helpful to know how to test it with my multi-tester and which wires to test for both continuity and resistence. 

is the ballast the device i asked about that is located on the passenger's side firewall next to the battery and solenoid? if so, could that be an issue and how can i test that? 

i'm pretty much tapped out due to the radiator repair and clutch cable repair on the VW Jetta and the repairs to my riding mower that are required to haul firewood since my truck is still down. i just ordered a solenoid for that today. i'm still screwing with the ebay seller concerning my radiator exchange...requiring another $15 for the price difference, and with UPS and FEDEX which seem to be able to find my house for delivery, but not for pickup.

i guess my point is that i need to be able to test for bad parts before i continue to swap and pray. excuse me if i seem like i am testy right now, but i am just getting a bit overwhelmed with a dozen projects going on all at once with absolutely no results and seemingly no hope. i should be out filling my 4 deer tags during the last week of archery season, but instead i have been screwing around here for the last week waiting for delivery folk that never show up.


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## HermitJohn (May 10, 2002)

I understand not having the money. No idea on the rubber covered thing on the firewall. I would assume some gizmo for pollution purposes. Whole row of that stuff on right fender of my Ranger with wires going to it and used to have vacuum hoses going to and from. Sure it made some EPA guy smile because it reduced some kind of emission 5 seconds after starting and cut out of the system 10 seconds thereafter. In real world it has no purpose. On a 25 year old truck its pure decoration and you couldnt buy a replacement if you wanted to (and actually could figure out what it does) unless you found one in junkyard. My F250 still has decorations from its days as a diesel long before I owned it. I do know enough about Fords diesel system from that era to know its part of glowplug relay setup.

Enough carp, I got lucky and found this page: http://www.autozone.com/az/cds/en_us/0900823d/80/11/ea/ea/0900823d8011eaea/repairInfoPages.htm

It even has description of how to test the resistance circuit. If for some reason it doesnt fit your application (some duraspark modules had different color wires I think) then search the Autozone site for info on your truck.

The ballast wire needs to be 0.6 to 1.6 ohm. So you could just use ballast resistor from say a sixties era Dodge. Various makes/models cars from that era used either ballast resistor or the resistance wire. All Chrysler products used an actual ballast resistor. New one at parts store is like $3. Even 70s era Chryslers with electronic ignition used ballast resistor, well actually it used a dual resistor with four prongs, but one side was standard 1 ohm resistance used on point ignitions. So if you were hotwiring a Ford duraspark module you want to find standard one ohm ballast resistor.

I like simplicity of GM module, about $16 at parts store but am cheap so guess if I already had bought new Duraspark module or had good used one, I'd use that and go buy a $3 ballast resistor if needed.

I did run across a Ford forum where some guy put new 302 in his 71 pickup and upgraded to Duraspark. Said he didnt use resistance at all and had put 40k miles with no trouble. Another guy said he'd went through several modules until somebody clued him in that he needed a ballast resistor. First guy replied he thought second guy was just getting too much heat where he placed module. Remember both these guys had older trucks that they added duraspark ignition. I think you do need the resistor or resistance wire in circuit, but just mentioning this to let you know there are different opinions. In my life, I've owned 2 Jeeps and an old AMC Gremlin with Ford duraspark module and never had any problem with ignition. Never had problem with GM HEI ignitions. Lot of trouble with Chrysler electronic ignition. I had to carry spare module and spare ballast resistor when driving that old '76 Dodge pickup I had. Didnt know how interchangable these modules were back then or I would have swapped to GM module on it. Volvos I had over the years used $250 Bosch module that was special order (Bosch is German for expensive, but you own a JETTA so already know that). One went out on me, thats when I figured out I could use $16 GM module as I sure as heck wasnt going to spend $250, would have junked the car first or more likely scoured every junkyard in the area. The Japanese modules are expensive too and also replaceable with GM module.


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## HermitJohn (May 10, 2002)

Ignition ballist resistor $2.19 at RockAuto.com for a '67 Dodge D100 so even at NAPA locally shouldnt be over $5. This should be a one ohm resistor and certainly meet the 0.6 to 1.6 ohm requirement for Duraspark module.


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## Rocky Fields (Jan 24, 2007)

Hey.

First step is to replace coil to cap wire. This needs to be a new, so it carries max spark from coil. NAPA used to sell the coil wire seperately for about $7. The electronic ignition FORD had in those days used to burn up the coil wire so often I used to carry a spare. The control module used to only last one to three years also. Usually when the control module was going out, the engine would kill suddenly and wouldn't restart until everything cooled down.

If that doesn't do it, replace cap and rotor. For bucks down, you can use a knife to lightly scrape corrosion from 6 metal contacts inside cap and wirebrush or scrape corrosion off end of rotor. 

I trust battery is good and charging properly...

RF


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## Rocky Fields (Jan 24, 2007)

PS: I don't have a pic of device mounted by battery, but I'll guess it's the voltage regulator


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## MELOC (Sep 26, 2005)

it's pretty much all new. the plug wires may be the oldest components...not sure how old, but it's worth a look. new distributor, module box was new last year and the truck sat since then. the coil is new, but sat as an extra in the shed for a year or three. the battery is only about a month old.


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## HermitJohn (May 10, 2002)

I suspect bad ground if anybody is going though Ford duraspark modules, also might check what brand of aftermarket module you are using and switch. The Ford module is more cumbersome but is just as durable as the GM module. As I mentioned, I had total Ford ignition on two Jeeps and one old Gremlin and not one problem with ignition in any way.

I saw website suggesting best brands of GM modules, some last as well as OEM, some dont last at all. I have one from RockAuto.com and one from AutoZone (Standard brand I think) and both have done ok. The AutoZone one replaced the 1975 OEM GM one for me and solved problem I was having with hard starts when engine hot. I think OEM one didnt retard ignition any when starting as it was one of first HEI modules ever mass produced. HEI system became standard in 1975 model year.


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