Swapping carb disty with FI disty

[tooldude]

Has anyone swapped out the carb model disty with a FI model disty? I would like to change out because that carb ICM seems to sell around $180. If there is information on this it will save a lot of research. It looks like the critical point would be whether there is an appropriate voltage coming from the FI disty. Both are sending a PIP signal to the processor with a one wire setup, and both are creating that signal from transistorized circuitry (maybe the same final transistor), and it's just a voltage pulse anyway. I'm venturing a guess those signals are the same/close. Why? because all the ECAs have two tables: the base tables, common to all, and the specific calibration tables for each model. I don't have a running FI car or a scope to compare. The voltage on the PIP signal MAY can be successfully checked with a DVM on MIN/MAX setting, but the scope should be definitive. The other consideration is the different advance curve, which may actually run OK though. Although I haven't compared yet, I'm venturing another guess that the advance mechanisms will change out. Anybody have actual knowledge on this?

[drddan]

Well the carb icm is in the disty, the efi ecm is outside the disty. I suppose anything can work, especially with the elec knowledge you have!

I have bought carb icm's on ebay for under $50. I also take them out of jy festy disty's once in a while
Swap it out with the one in my disty for testing. If its good I just leave it in there and put away the one I pulled.

You can also put a MSD ignition in a Festy!! Just run the wires from the MSD unit into where the festy icm plugs in. Voila! No more dieing icm's.

The carb icm reqires a 3 ohm coil. Using an aftermarket coil, which is usually 1.6/1.8 ohms, will burn out the icm prematurely.

[tooldude]

Thanks for the tips. I just try to keep my vehicles running and dependable so no experience with modifying things. I was just recently glancing over the MSD site to see if there is something to run off that armature and ideally have programmable spark advance. It was a quick look, I didn't see anything. Is that the setup you're refering to? I was dreading this might take all kind of modification without something aftermarket and then be better to just go on to the FI switch, which I don't want to do at this time.

[1chrisapple]

tool dude I just got done swapping over my b3 to run msd 6a that I found used for $20. I took the bad ignition module I had and took the aluminum backing off.gutted the insides out and soughtered some wire onto it and its doing great so far. if u wanted to send me ur bad module I could do it for u for like $10

[Banana Bonanza]

If you have a carb Festy, you need vacuum advance The FI Festy distributor doesnt have one and is not made so you can add one. Computer controls ignition advance on FI Festies. The vacuum advance controls ignition advance on carb Festies.

You will need to either repair what you got or find a good junkyare carb Festy distributor.

The carb ignition module is available separately for around $50 on ebay I think. Personally I have adapted the $20 four prong GM modules from 70s era on various make cars with vacuum advance distributors with good luck and probably try that if module goes bad in my Festy.

I did replace the faulty vac advance on my Festy distributor with aftermarket one made for GM V8, its the adjustable kind. Gave like $10 on ebay. Had to custom make bracket to hold it. Alas FEsty vac advance no longer sold separately.

And lastly reluctor and pickup coil that signal the ignition module could go bad. They used to be available separately, but not any more. You'd really have to get lucky to find ones from something else that would adapt. So at that point you either find a junkyard distributor or pony up for the rebuilt one. Though you might check around at Mazda dealers just in case they had some from old carb 323.

[WmWatt]

drddan: Haynes manual says coil primary winding resistance should be 0.8 - 1.6 ohms for 88-93 models.
Are you saying 0.8 - 3 ohms for 88-89 carburetted models?
Thanks.

[drddan]

Well .... according to Jim, not the TV show! but FB71 on here was a ford techician and he has stated the coil needs to be 3 ohm for proper operation and longevity.

My Haynes states the same as yours does WmWatt..... but if you look it up, BWD has a coil that is 3 ohm and states it is for our application. It may be the 88-89 carb models years only, I am not sure about that.

I have a Mallory hi-output coil, reads about 1.6 ohms. Didnt have it in long at all and ECM burned out. Thought it was just its time, and got another ECM.
Wasnt long and poof, it went too.
Jim suggested using the stock coil because of the ohmage. I did and it has ran for years. No ecm fails since. Coincidence!? I think not.

[drddan]

Come to think of it, I would bet money that it is that 88-89 carb ecm only. It is a different creature than the rest.

Here are some amazing little known facts about the carb'd festy's:

The 88-89 carb choke wire from the alt only puts out 7 volts. If you switch to a Weber carb, you will need to find a 12V key on source for proper operation of the Weber choke

It is suggested to use "Heat-sink Paste" under the carb ECM, as the enemy for the ECM is heat. White heat sink paste avail at radio shack
Again, according to JIM, the lower ohm coils cause more heat, thus killing the ECM.

I pulled out an ECM, about 2 weeks ago, from what looked like a new disty at a JY and guess what? There was fresh white heat sink paste under the ECM!

My original ECM that died, had hard, dried up, brown looking paste under it, thus not doing its job of helping to keep the ECM cooler.

[WmWatt]

Thanks for the info.

White heat sink paste cheaper at electronics stores. The local store here has a container of them on the sales counter by the cash register, $1.25 ea and good for two ignition control modules.

[Banana Bonanza]

The 88-89 carb choke wire from the alt only puts out 7 volts. If you switch to a Weber carb, you will need to find a 12V key on source for proper operation of the Weber choke\

My Weber has a coolant heated choke! Last I knew, coolant choke doesnt need 12V to operate.

Or the true die hards can do a manual choke. I am getting old and appreciate an automatic choke myself. Keep forgetting to push the choke in on cars with manual choke.

I actually like the hot air chokes used on older american cars. They were quite effective until the tubing rusted. But bit of new brake line solved that in short order. The hot water chokes next, though they can corrode and start leaking. But really suppose auto chokes are just laziness. You get a decent choke cable and keep it lubed and manual choke will last life of the car. I even had a 1972 Courier with an ingenious little spring loaded dohicky to retract choke cable once you are at higher speeds if you forget to manually do it. It was a so-so compromise for sure (tended to open choke too quickly), but it kept me from heading down hiway puffing out clouds of black smoke.

[tooldude]

Lots of good tips here. Thanks everybody! I don't have a running FI to make checks. I completely forgot what I had researched about that advance, back when I was not getting sleep. That coil resistance is very important, because in a DC circuit cutting a resistance in half will double the amperage and that can generate a lot of heat. In old cars you could mistakenly put a 6V bulb in a 12V application and sometimes they would last a short time, burning so bright you would immediately know what happened, then pop out.

[drddan]

My Weber has a coolant heated choke! Last I knew, coolant choke doesnt need 12V to operate.

Ha! You're right there!
.... and I dont think the coolant and electric would play well, either!