A long time ago I bought a 7747 kit from a business called CustomEFIs to convert from carb to TBI. The kit came with a new distributor to drop in, and I hooked it up to my large (coil-in) cap and have been running it ever since. I'm now coming to realize that this is an unusual setup, and that most all TBI setups have a separate coil. It's no big deal, but I'd like to understand what I have. Are there any factory setups like this, or do I have a one-off custom thing?

Here's an old pic I took of the distributor before I installed it. Looks like 5 wires to the distributor itself and another connector to hook up to the cap. Can anyone shed some light on what I have going on?

 

Same as you, I've never seen a large cap distributor used in a TBI set up. Although there could have been one.

The large cap distributors were used in many CCC and EFI set ups, such as the early MAF TPI f-bodys, and the entire line of y-body TPI set ups. So it will work in your application.

The pre-TBI CCC trucks (E-q-jet) also used the large cap distributors.

RBob.

 

I went out there and started poking around, plus refreshing my memory of how the connections work on a coil-in-cap distributor. On my original carb setup, there were three wires from the dist base to the cap, these are coil+, coil ground, and coil-. These go to a three pin inner connector at the cap. The outer connector has two pins which are electrically in common with coil+ and coil-, the coil+ being +12 ignition input (the module taps ignition power here) and the coil- being the optional tach output.

So in my new setup, the TBI distrib has two wires at the base which are just coil ground and coil-. The guy who built my harness maintained the third connection at the inner connector as a means to get ignition +12. Additionally, there's the normal 4-pin connector to the module.

So in the end I guess it all makes sense. The system doesn't really care where the coil is and I've simply got a few things routed to the coil-in-cap connector. It's a clean setup and I've got space for it, so I think I'll stick with it.

Thanks for chiming in RBob, this is what I'm using with my EBL-Flash setup now.

 

If your keeping the Large Cap HEI, then there will be some
"SA - Spark Latency Correction" adjustments needed as well.

 

What does that do?

 

The only TBIs I can think of with the large cap HEIs were actually crossfires.

 

CCC HEI are compatible with TBI. Just have to re-do harness ICM interface plug from a compact plug to a flat 4 pin plug. Very common when converting CCC car or truck to TBI. One less thing to buy. IRC I've posted a detailed write-up few year ago.