Wiping out Duraspark boxes.

[wyldstallyn73]

When I completed my current buggy, I was running a stock Ford Duraspark ignition with no issues untill I swapped in the stroker engine with a MSD dizzy and Digital 6+ brain box- all was good untill a couple of weeks ago when i went to load it for a work day at the local wheeling grounds and it wouldnt start. After determining that the Digital 6+ box was no longer functioning, I just loaded the spare beater rig and left. Now with Labor Day weekend wheeling coming up fast, I decided to just go back to the DS setup because the magnetic pickup unit in the MSD dizzy looks to be the same as the one in a Ford dizzy. My original DS box and wiring was still on the rig, so it was fairly easy to do, but I had to do a partial disassembly on the MSD dizzy for some corrosion cleanup and splice the ford harness connector to the msd pickup unit- there's also a third wire on the ford harness end that grounds to the inside of the ford dizzy, but I clamped it to the outside of the MSD dizzy. It ran fine, even better for throttle response I would say, but the next day when I went to move it from the shed, it would not start. Found that the DS box was dead- changed it out with the spare I was still carrying in the rigs tool box and all was well again untill I wanted to load it on the trailer today- that box was dead WTF!!!! Granted, they are used boxes from my parts stash, but what are the odds that they were both just ready to go?? I have always ran the DS system in the past with outstanding reliability- a dead box few and far between. I changed the dead box out again for my last used box and loaded it on the trailer- we will see if it works tomorrow, and round up some more from my personal junkyard. The cap terminals inside the dizzy were pretty damn corroded, and I did a quick and dirty job of cleaning them up with the intention of getting a new cap when I go to town Friday morning.

Any ideas what's causing this?? maybe whatever is knocking out the DS boxes took out the MSD too??

351W bored and stroked to 420, running on propane
aluminum Trick Flow Twisted Wedge heads
Accel Super Coil (big yellow bastard) and wires.

I don't want to hear about going to an HEI dizzy- there's no time for that right now, and it might not fit anyway because the MSD dizzy was the taller one to clear the Edelbrock intake manifold.

[jopes]

the DS boxes are pretty strong little things. as for whats nuking everything, I got no idea.

things you could try are, swapping in a different coil, with a new DS box and be sure all the wiring is correct as well as nothing is shorting out.

I had a MSD take a shit, MSD would not repair it becuase it was a offroad box. Well I working on SEFI and in the mean time I swapped in a dizzy with points and a VW coil and goddam it woke the engine up with more power than the MSD ever had.

[Gremlinstien]

Add a ballast resistor to the power feed side of the coil.

[wyldstallyn73]

Originally Posted by Gremlinstien

Add a ballast resistor to the power feed side of the coil.

Not saying you are wrong on this, but that shouldn't make a difference. I used to add the ballast resistor on all my Duraspark wired projects, but others told me the basllast resistor was only required for a points distributor. One day when wiring up a project I decided to try it without the resistor- worked fine, and I stopped adding them ever since with no problems.

Can you give me a theoretical reason why I should utilize one??

[jopes]

don't quote me on this one because I have not looked at them much, but I do beleive the DS has a built in the harness ballist resistor, you would have to check the books on it.

[wyldstallyn73]

Again, not saying I am absolutely right about the ballast resistor being an issue, I am just skeptical.

On the old points distributor vehicles there was a calibrated wire in the harness going to the coil. I have gutted out a lot of mid-late 70's Ford cars when I was doing demolition derby and never noticed such a wire for the Duraspark, although admittedly I was'nt really looking for it. Could be a case of it having a different appearance than the older points type too.

[mikepotts]

Originally Posted by jopes

don't quote me on this one because I have not looked at them much, but I do beleive the DS has a built in the harness ballist resistor, you would have to check the books on it.

i have done several DS retro fits and have had several burn up on me with no warning...some have went months before trouble, then WHAM, ive been doubting the resistor thing, but in tracing the diagram i have seen one in the stock harness also....cant hurt to try. as for the MSD, if it requires one, MSD should have had it in their install diagram, which i dont think they do.

[FordFascist]

I've run them both ways, with and without ballast resistors and it hasn't made much of a difference in reliability.

I have two guesses as to what is killing your modules:

1) Somewhere these is an interruption in ground wiring which would cause an high-voltage back feed into the ignition module.

2) Constant or extended source of power to the coil and or module.

The easiest way to isolate this is to have both run off of separate relays or a diode so there is no possibility back feeds. I prefer relays because they are easier to find, as diodes can be difficult to locate when you need to troubleshoot. Occasionally stereo amps can back feed +12V through the ignition wire, energizing the coil and thus causing a power spike to the module.

[wyldstallyn73]

Originally Posted by FordFascist

I've run them both ways, with and without ballast resistors and it hasn't made much of a difference in reliability.

I have two guesses as to what is killing your modules:

1) Somewhere these is an interruption in ground wiring which would cause an high-voltage back feed into the ignition module.

2) Constant or extended source of power to the coil and or module.

The easiest way to isolate this is to have both run off of separate relays or a diode so there is no possibility back feeds. I prefer relays because they are easier to find, as diodes can be difficult to locate when you need to troubleshoot. Occasionally stereo amps can back feed +12V through the ignition wire, energizing the coil and thus causing a power spike to the module.

Would'nt scenario #1 result in the brain box dieing while the engine was running?? So far, the boxes seem to be fine while running, but when I try to start it the next day, it's dead (or perhaps it is nuking when I first turn the key the next day)

Could you elaborate a bit on scenario#2?? are you saying the ignition is getting power while the switch is off??

[Southern_Pride]

Ive given up on em. When I run em with no resistor I blow em in like 2 hours. With 2 resistors I could get about a week out of one. Never did figure the cause. But I have a factory electrical and vaccuum manual and it should have a resistor or ballast resistor wire.

[desteurm]

What about a RFI capacitor or voltage regulator, perhaps you are getting power spikes wiping out your duraspark? I remember reading somewhere that MSD makes a regulator that prevents this shite from happening.

Something like this

http://www.msdignition.com/product.aspx?id=4659

Page two top paragraph

http://www.msdignition.com/uploadedF...adio_noise.pdf

[jr4x]

My bet is a low voltage going to the box while the ignition is off (you think). I have ran duraspark ign's in circle track race cars that would go bad every single time I left the toggle switch on. Also had a van that for some reason would burn up a DS box every night till we figured out to unhook the battery. The steering column was messed up and would give power to the box while the key was in the off position. The ds box doesnt seem to like having power that it cant get rid of. Check the positive for the box and I bet you find residual power.

[emsoffroad]

There are two power wires going into the box.

I forget what color is for what. One red one white. The one gets the full 12v from the "I" post on the start relay. The other does not get a full 12 volt in the run. They did this two ways. The ballast resistor or a resistor wire in the harness, depending on year.

I would guess that if you took the MSD out, you hooked spliced the stock back in, maybe somehow you by passed the stock resistor wire in the harness.

[FordFascist]

Originally Posted by emsoffroad

There are two power wires going into the box.

I forget what color is for what. One red one white. The one gets the full 12v from the "I" post on the start relay. The other does not get a full 12 volt in the run. They did this two ways. The ballast resistor or a resistor wire in the harness, depending on year.

I would guess that if you took the MSD out, you hooked spliced the stock back in, maybe somehow you by passed the stock resistor wire in the harness.

Fords use a resistor wire to the coil. The DS box receives 12V power in the run position. I think it's heating the coil and keeping the box on when the key is off. It's entirely separate from the resistor wire in the harness.

On a blue DS module, red wire = run, white = crank.

[JGVABronco78]

My bet is with power to the box when ignition is off. Try unplugging the box every time you stop and see if it lasts longer. Next bet would be short on hot wire to coil, or possibly interuption to ground. I've always been told that the ignition voltage for the DS is 7 to 9 volts, and the white wire coming from the I terminal retards the timing in the box for starting, and the red wire is power from the key on position when running. I'm also told only the Motorcraft boxes have this feature and remakes do not.

[jr4x]

Originally Posted by JGVABronco78

My bet is with power to the box when ignition is off. Try unplugging the box every time you stop and see if it lasts longer. Next bet would be short on hot wire to coil, or possibly interuption to ground. I've always been told that the ignition voltage for the DS is 7 to 9 volts, and the white wire coming from the I terminal retards the timing in the box for starting, and the red wire is power from the key on position when running. I'm also told only the Motorcraft boxes have this feature and remakes do not.

All DS II boxes are 12 vlt. The early DS style were resisted to 8 vlt untill the new version came.

I put DSII in my jeep on a ford small block its wired up with only the 12 volt constant hooked to the red on the box. Nothing hooked to the white. If you put power to both those wires at the same time the box is smoked.

[JGVABronco78]

Originally Posted by jr4x

All DS II boxes are 12 vlt. The early DS style were resisted to 8 vlt untill the new version came.

I put DSII in my jeep on a ford small block its wired up with only the 12 volt constant hooked to the red on the box. Nothing hooked to the white. If you put power to both those wires at the same time the box is smoked.

12 volts to the box, but 8 volts to the coil unless I'm confusing it with something else. I know Ford chokes are only 6 to 7 volts by powering from the alternator stator, but I'm pretty sure the coil voltage is 8 volts by means of a resistor wire. Not 100% sure though. The main point I was trying to make is the white wire retards ignition, not reduce voltage as was mentioned, that it may not have 12 volts to the coil due to resistor, and that constant power to the box or a short could be frying the boxes.

[wyldstallyn73]

Pretty shure the theory of the box getting juice when the engine is not running was the correct problem in my case. While I did'nt loose any more boxes over the Labor Day Weekend, I had some quirky starting problems that make me believe contacts inside the parts store "universal" switch in my buggy arent lining up quite right all the time.

thanks for the help, and continue with the discussion of wiring the DS box if you wish- it is interesting hearing how others have done theirs and what their results were/are.

[dahoyle]

I have had a few of them go bad when I left the key on but the engine off while checking lights and such. It doesn't take very long at all. It wouldn't surprise me at all if that was the problem.

In my old Jeep, I carried a spare in the glovebox for just such contingencies. They almost give them away at the salvage yard I use, and it's cheap insurance,and only takes a moment to swap.

[JGVABronco78]

Don't know that much about the actual physics of the thing, but I wonder if it has anything to do with where the trigger stops in relation to the pick-up coil, or if they're just weak boxes prone to failure. I've left them on overnight, and still worked fine. I've seen people leave them on for 10 minutes checking stuff and poof, gone. I used to have one that had the sealer cracked in the back and wouldn't start when damp out, but I could leave the key on 10 or 15 minutes, then it would fire up and stay running. Then I started taking it in with me at night and leaving it on the top of the hot water heater so it be ready for a quick start in the morning no matter how cold or damp. That worked good for a couple of weeks till my coil fell on the block, shorted out, and blew the back of it slam off. (Really just all burnt up)

[Oatmeal]

I never had any major problems with the modules in my '74 (Ca.) Bronco but, I hated the fact that you always had to get the correct year (colored strain connector) module, that wasn't always available from the auto parts store.....that and the original wiring getting old and brittle over the years. I just wired in a Mopar module (Standard Motor Products LX101) and have been happy ever since--------Hans

[wyldstallyn73]

ChestonScouts thread reminded me that i should update what the REAL issue was on mine-was not the ignition switch, but it turns out it was the pickup unit inside the dizzy- some boxes it would run with, others it would not, changed it out and all is well. I will have to scrounge the DS boxes that I threw in the junk truck that I thought had fried and try them again.

[mj]

so you didnt get out your DVOM before you blamed the duraspark design huh?
my rebuilt dizzy had the pickup die 1 week outa warrantee, used the autozone website duraspark section to track down what died.

[solidrunner]

I was having the same problems and then I ditched the duraspark box all together. You can use the pickup in the distributor as the crank trigger for the MSD box. I used a stock duraspark distributor and 6al box for years with no issues. You only use two of the wires coming from the distributor (i don't remember which ones) and run them to the green and purple wires on the box. MSD's website should tell you which wires to use from the distributor.

[wyldstallyn73]

Originally Posted by mj

so you didnt get out your DVOM before you blamed the duraspark design huh?

Never blamed the Duraspark design to my recollection- matter of fact, I am a big supporter of it for the most part.