Hey guys. This is actually for a GM truck application, but I know the experts are here. I hope it's okay.

I have a 1983 K5 Blazer that I converted to 7747 TBI with the help of a long defunct vendor (7747 since upgraded to EBL). Somehow along the way we swapped in a computer controlled distributor base, but kept the coil-in-cap setup. The wiring is somehow adapted to this setup. Now that everything is getting old and I'm starting to have some issues, I really want to put in a "normal" distributor: 2 and 4-pin connectors exposed at distributor base and external coil. I could really use some help figuring out how to map the wires I have currently to the 2 and 4 pin connectors (and coil).

This is the kind of distributor I'm thinking about:


This is the wiring I'm aware of:

But when I open up my current distributor I see this. I have the 4 wires on the left, which presumably would hook to the 4-pin connector on the new module. But on the right I have 3 wires entering the distributor instead of two. One appears to simply be grounded, but there's also that big capacitor. Is it not needed in the newer/other setup? Would I just ground the wire that is grounded externally to the distributor? I guess more generally, if someone recognizes this distributor, I could try to find a wiring diagram and maybe that would help.



This thing looks like it's an adaptation of a non-CC distributor since it appears to have spots for springs and weights. So I don't know what that guy stuck me with here, the more I think about it. If anyone could help get me on the right track, it would be greatly appreciated.

 

Thats an older HEI adapted to a CCC or early TPI ignition module. My 1988 307 Olds had the same style module.

A standard TBI distributor could easily be exchanged although I like the coil in cap HEI setup better. Davis Unified makes a really nice replacement but it is about $300 when said and done.

The capacitor is the condenser and it needs to be there to prevent the module from being killed by the voltage spike of the coils field collapsing.

I do not see anything wrong with the way this one was modified. Vacuum and centrifical advance seem to both be deleted and locked in place. I had one just like this on my G20 van, I swapped the main shaft to a TPI Corvette one I had from a damaged housing to delete the centrifical advance. I used a quick adjust timing advance **** for the vacuum advance lockout. Back when I was tuning with UV Erase proms it allowed for easier base timing adjustments for dyno tuning total advance. I remember well that 1/2 turn of the **** was 1° and it was so accurate once I had the base timing adjusted, it was very easily to accurately tweak the base timing for more or less total advance.

 

Thanks. If I go with a standard TBI distributor, I can just make the connections per the wiring diagram, no capacitor, no extra ground wire, etc.?

In general, it would make my life easier to have my setup match a factory wiring configuration so when something goes wrong in 3 years I have resources to refresh my memory on how things are supposed to go and what parts to buy. It's worth some money to make that happen. New distrib plus coil would be about $300, like you say, for aftermarket performance items, or maybe $150 or so for factory style replacement.

 

Buying a "new" distributor is crazy when the Treasure Yards are full of '87--'95 pickup trucks (and other applications) with distributors, coils, and the Weatherpack connectors you need, probably for $50 for the whole works including plug wires, usable cap 'n' rotor, etc.

Beware certain B-body distributors. They may have housings that aren't compatible.

 

Thanx for sharing...I need to see pictures like that. Just a couple of days ago, I unwrapped the nib Pontiac HEI distributor housing to see what needs to be transferred from a Chevy HEI for a TBI retrofit on a Poncho engine. Nice to see the single screw to lockout the advance as I was looking at the 2 holes maybe nut and bolt as long as the head of the bolt is big enough to run interference.

Ironically I need to go from small cap to big cap.
https://www.corvetteforum.com/forums...-for-87-a.html

 

"Nothing" needs to be "transferred". None of the Chevy TBI distributor parts are compatible with the Pontiac housing.

You need a computer-controlled (no vacuum advance, no centrifugal advance) distributor from a 1980s Pontiac. This will have a 7-pin HEI module, not an 8-pin or 4-pin module. Drop it in, splice in the wire harness. I think the 7-pin module will work if the wires are connected properly.

Worst-case, you'll need the 8-pin module from the Chevy housing, you'll have to figure-out how to mount it 'cause it won't fit the Pontiac housing. You'll have to get clever and figure out how to connect the Pontiac pickup coil to the 8-pin module. And you'll want the 2- and 4-pin connector bodies with pigtails to plug into the module, and splice into the vehicle wire harness.

 

The last year of the 301 had a computer controlled carb.