Got a 89 F-700 with 429 engine--------runs Duraspark II ignition system.

Have asked questions here before------but need to refresh my "faded memory". Had problems several years ago-------and solved by running the "Chrysler style" resistor bypass across to the coil wire.

Later mice had a field day under the dash--------and my serviceman/helper completely rewired everything from under the dash to the radiator. (didn't like my "Rube Goldberg wiring"-----so ditched it) Got the truck to running-------but have had one ignition problem after another. I am satisfied that we are missing the original ballast resistor feeding the ignition coil.

Coil heats up in just a few minutes. I want to go back to my simple wiring scheme (to which Franklin 2 has recommended several times on this forum). It ain't factory-------but it runs!!!

Currently------we are using the coil that is designed for "electronic iginition". Apparently-------this coil is different from the coil that states it is designed for "external resistor". My serviceman insists that you don't need the resistor step down if the coil is an "electronic ignition" coil. Supposedly the resistance is built into the coil------so it cuts the voltage down. This may be fine and good as long as its running-------but then the coil is hot and you are trying to crank off again on low voltage-----which usually doesnt work???

Question: when running the "Chrysler in line ceramic resistor"-------should I be running a coil designed for an external resistor; --------or will it be OK to utilize the original coil designed for "electronic iginition".

Looks to me that the original "electronic ignition" coil was dependent on 12 volts for start--------and then to run on 6---8 volts (so it still needs the step down). If I remember correctly-------the Chrysler resistor cut voltage down to approx 9 volts after it warmed up???


How about it Franklin 2-------------or some of you other gurus????



Sorry to be so long winded---------but hope ya'll are able to follow my thinking.

Got a couple more questions-------but we will get them later.


Delta Dirt
Avon, Ms 38723

 

the duraspark coil was supplied by a long resistor wire in the factory harness, and needed that resistance to last.
the TFI coil used on later trucks is designed to run on a full 12v with no resistor, and might be a good option for you.
you could also set up a ballast resistor like an old chrysler has, and supply a duraspark coil with it.

i once had a car that ran well using a duraspark distributor, GM HEI module, and TFI coil in place of the stock duraspark system. the system worked great for me, though others give mixed reviews of it.

at the end of the day, a coil made to run a full 12v will handle it just fine, a coil made to run with a resistor will need one.

 

The duraspark II system needs a resistor, period, no matter what coil you run. If you use a TFI coil that does not require a resistor, you are still sending all that high current through the duraspark module. The HEI system and the later for TFI system do not need a resistor, because they have internal circuitry that regulates the current through the coil and the module(the module has the reg circuitry).

To the original poster; They do make coils with internal resistors. They are usually marked. But even if you did have one, they will not work well with this system. That's because you would not be able to run the resistor bypass to get full voltage during cranking. This feature helps give a hotter spark during cranking to help combat what you are talking about, the low voltage during cranking, especially in really cold weather.

I would get a duraspark II coil, one that is made for this system. You might need to buy the horseshoe connector to fit this coil, it usually has pins on the top instead of threaded studs.

Find your wire from the keyswitch, and run it to the Chrysler resistor. Run out of the resistor to the coil +. All the rest of the wiring should be ok, there will be a wire running from the neg of the coil to the module.

Look at your starter solenoid. If it has two small terminals, one will be labeled "i". Put a wire on this terminal, and run it around and attach it to the resistor terminal, the one that goes to the coil +, not the one that comes from the keyswitch. This "i" wire will put a full 12v on the coil while cranking helping it fire off quicker.

 

Thanks Franklin 2---------you have explained it in terms that I hope my serviceman/helper will understand.

This guy is a really good old country boy that seems to most anything run------(at least for a little while). Just don't think he has ever fully grasped the Duraspark system---------particularly the fact about the resistor for the run side.

And--------my problem is that my hair has faded and the old "rememberer" don't remember what all it did a few years ago; can't do what I used to---------so gotta have some help. (I ran a 84 Bronco with the same ignition sytem for over 300,000 miles------was pretty familiar with the system back then------but that was several years ago now)


Got one more question concerning the Duraspark II system:

How important is the mechanical vacumn advance to the timing-------my "assistant" is under the impression that the ignition module (brain box) is handling all of the timing advance--------and has the vacumn advance on the distributor disconnected. Its my impression that this feature came with some of the later systems than the Duraspark II.

My thoughts are that we need to finish the job--------and reconnect the vacumn advance mechanism for maximun/full performance????

Thanks----


Delta Dirt
Avon, Ms 38723

 

the vacuum is required for proper performance, otherwise you'll be stuck at base timing. as you thought, its only later systems (TFI) that use the computer for that

 

The module does not control the timing on this type of system. He is getting it confused with one of Ford's other great ideas that didn't last long. The timing is controlled completely by the dist.

The vacuum advance is for fuel mileage. You have the base timing that you set with the timing light, and then you have the rest of the advance that the weights and springs in the bottom of the dist control according to the rpm of the engine.

The vacuum advance adds advance on top of the above two according to the load on the engine. With hardly no load on the engine, it can take a lot of advance to make it more efficient. With a light load, the carb is almost shut, and the vacuum is high, so the high vacuum pulls on the advance and advances the timing way up. When more load is put on the engine, you are pushing open the carb more, your vacuum goes down, and the vacuum advance relaxes and the timing is pulled back or retarded.

If this is some big dump truck that you have, if you run around loaded or with the pedal to the floor most of the time, you will not notice much difference if the vacuum line is hooked up to the dist or not. If after a run you are coming back unloaded and are cruising along pretty good at part throttle, you might see some MPG improvements by hooking it up.

You can prove your mechanic wrong, by looking around for a plugged off port with vacuum on it, and plug the vacuum advance into that. The rpms of the engine will raise way up(if the diaphragm in the unit does not have a hole in it). But on most engines, this vacuum line to the dist goes to a ported vacuum source, one that has vacuum only when you raise the rpms.

 

Thanks again to both of you.

That's what I've been thinking--------plenty of power with a load; ------
but thinking that we could clean up some fuel economy when running at light throttle with the vacumn advance working properly. Might help the fuel economy more than you think-----the truck has enough power that you are never really working/pushing the engine

We don't run this truck very much-------set up with a 16 ft dump bed for general utility here on the farm. (but it needs to be dependable when you need it)

Will get back on it in a day or so-------just need to get it back to where I had it before the encounter with the mice!!!!!!

Think I see the light----------now just gotta find the end of the tunnel!!!

Thanks----


Delta Dirt
Avon, Ms 38723

 

I am back again with another question:

Looks like we also burned the distributor pick up module out-----gotta get the distributor drive gear pulled so to change it out; --------so still don't have engine cranked.

questions:

With the statement "12 volts on start and 6---8 volts on run"---------
in the run mode: with the harness not attached to the coil, it reads 12 volts; attached to the coil, it reads 7.45 volts.

Should the voltage reading on run be with the wire attached to the coil----or disconnected from the coil?????

It appears to me that I am delivering the full 12 volts to the coil (based on voltage being fed to the disconnected harness connector)------and there is no resistor in the line.



And------while actually spinning the engine over in the start mode; meter was reading approx 8.5 volts (with the starter load)-------is this an acceptable reading???

My mechanic/helper is adamant that we don't need the resistor-----that the resistor is apparently within the wiring somewhere based on the 7.45 reading when connected to the coil.

Regardless-------we have to cure our "burned out problems" and get the truck back to running to fully determine where our problem is coming from.


Still scratching my head down here in Mississippi!!!!


Delta Dirt
Avon, Ms 38723

 

If this truck was indeed originally a durspark II system, and the original harness is in place, then yes the resistor is in the harness. If any wiring has been bypassed or replaced, then the resistor might not be there(it was a special resistance wire in the harness).

The resistor does not do it's job unless there is current flow through it. So if you take a reading on the wire with it just hanging in the air, you are going to get 12v. It's best to take a reading when the engine is running. That way the alternator is putting out around 14v, the voltage should be up everywhere, and when you take a reading at the coil +, you should get something lower, like 9 volts or somewhere in that ballpark.

Your voltage readings during cranking will vary, depending on how charged your battery is, and how hard it is to the turn the engine over. If you are cranking slow and only have 8.5v at the solenoid when the starter is turning, then of course you are only going to have 8.5v over at the coil also. That's why bypassing the resistor helps out during cranking.

Also, if this does have the original harness, and your solenoid does not have the two small terminals but only has one small terminal, then that means you have the resistor bypass built into the harness at the ignition switch. This is the way they did it on the later trucks. But that's ONLY if the harness is wired original and proper. If it has been redone and you don't have this feature anymore, then you can buy a older style solenoid with the two small terminals and wire in the bypass yourself.

 

Thanks for the clarification.

Does have the two prong solenoid------but don't know what is original wiring and what has been changed. I bought the truck used and the engine had recently been changed out. Whoever changed the engine out mangled/botched the wiring when installing the new engine. But I am satisfied that it came from the factory with the Duraspark II system------might well be that the resistor is still in place and he is working through it.

Earlier-------I had gone with the by-pass set up with the Chrysler resistor and had it running fine. Then the mice encounter-------after which I left it up to my helper to rewire. He didn't like the Chrysler resistor set up (saying the voltage was too low) and did away with it------truck seemed to run good; but have had to change out several coils at various usage time. Last time----------about 10 minutes (so something ain't rignt). And-------we also apparently burned out the distributor pick up module at the same time.

Definitely need to get cranked off---------so we can get some true electrical readings.

Also--------want to check the ignition switch out; make sure we don't have any shorts or cross feeds coming from it. Just about to get my helper convinced to go back and start from scratch with a simple by pass of all of the ignition wiring and use the Chrysler resistor. That way-------we are dealing with clean wiring and know exactly where and how much the resistance step down is-------and may be dodging other hidden wiring problems at the same time.

My helper is old school-------has some preconcieved ideas sometimes----a little bit hard headed; ---------but has the reputation of making the older stuff run when nobody else can. I am 70 with a pile of health problems-----he is 10---12 years younger-----but has some old buddies that he confers with on a regular basis. Finding someone willing to tackle these older vehicles with the early electronics is really getting to be a problem.


Will keep you posted--------and maybe others will be able to pick up helpful information off of this thread. ---------thanks.


Delta Dirt
Avon, Ms 38723

 

Could you please name the duraspark II coil you are talking about. I have looked all weekend and found no coil that is earmarked duraspark II coil. So a model number, make or anything less vague would really really be helpful as I broke the front plastic off on my 1981 ford f100 duraspark II coil and need to replace it, cause that plastic front held the green wire connector onto the button.

Am I still in the 1980-86 forum?

 

Autozone part number C832VC $22.99 or the better quality one is C832 for $28.99 See it has pins instead of threaded studs. They also sell the connector that slides on to these pins.

 

I just replaced the coil in my 81 F100. Went to Autozone, told them what I had and took the DuraLast model. Don't know how long it'll last but it was the one I needed.

It sounds like you're talking about the horseshoe connector that holds the two coil wires, no? I also picked that up at Autozone. "Coil connector" for about 6 bucks.

EDIT: What he said.