My stock points distributor to computer controlled HEI conversion

NAPA shows chevy 350 trucks from 1987-1995 as having the 8-pin HEI modules. I also know the f-body TPI engines had it too.

 

Here are some pics.
Pinout:
G: ground
E: spark timing
R: tach reference
B: crank override

+: +12v
C: coil channel

P: +VR (grey)
N: -VR (green)


So what computer controlled ignition are you running to control the 8-pin HEI module? Are you currently running a 4-pin with the MSD box and magnetic pickup?

 

Thanks for the pinout, that helps! My current distributor is a points-type that was converted to a magnetic trigger to fire an MSD box. Dave at www.davessmallbodyheis.com did it. I've had the gear to put in a 4-pin module as a backup in case the MSD box failed, but never used it.

I'm about to make the jump from Q-jet to Holley ProJection 4Di, which will also control the ignition timing - thus the questions about 8-pin modules. :beer

Since I'm going to need a new coil, and I'm going to have to lock out the mechanical and vacuum advance, and my old magnetic trigger may not be the best for an 8-pin module...I may well end up selling my current ignition setup and doing like you did - convert the guts out of a newer HEI distributor into a donor Buick distributor body.

Hmm....looking at the Megasquirt page (http://www.megamanual.com/ms2/GM_7pinHEI.htm), looks like you feed power to the whole system through the "extra" connector on top of the coil, and the other "extra" lead goes off to a tachometer (and the ignition system gets its tach signal from the "R" pin on the module).

The "B" pin wants 5V while the engine is running, but 0V while cranking (so you have no advance I suppose). So where do you pull that switched signal from on an older car (I've gone blank on ignition switch wiring at the moment....)? And could you hook it up with everything but the E, R, and B leads and have it work like a 4-pin module - just for troubleshooting?

 

Yes, you could hook up everything but the E, R, and B pins and it should run with the module's built in 10 deg BTDC locked timing.

As far as hooking up pin B you can just hook it up as shown in the diagram on the megasquirt page you listed. That relay can be hooked up with it's coil connected to something on the car that is off while cranking but on while running. Maybe the AC blower circuit? I'd have to check my 69 buick manual to get a hint on that. And the contacts of the relay should be able to use the +5v reference from your Pro-Jection system. I tried to look up the 4Di on Holley's site but could not find it. It doesn't look like their 2D system control ignition?

And yes, that bare pink wire in the pictures is the main +12v feed for the coil and it gets passed through to the module as well. And the other white wire with the single pin connector is for the dash tach I believe. But if you want to run a regular coil you can just hook it up as shown in that megasquirt diagram.

 

Great. Didn't know about the 10 degree timing though, thanks for the info.

Yes, the blower and most every other accessory. I went blank on it, but my wiring diagram gives me some ideas.

Yeah, Holley doesn't want to be helpful in supporting this "old" system of theirs, they'd rather I spent $1K and got the Commander ECU - but I'm a thrifty Scot, so there ya go! :laugh:
Anyways, I can't find a good schematic of the 4Di either, but I'm pretty sure I can tap into the TPS. The Holley manual mentions disconnecting the TPS to set the base timing advance. Odd, it talks about connecting to a GM module, but they're conecting a 4-pin connector to a 7-pin module (which would be the less-common 'small' 7-pin module). They don't mention any other GM ignitions, grrrr. Have to do a googlesearch on '4Di pinouts', I guess. I'd think the 4Di is very similar to the 2D system, as well as the Commander - as far as the wiring, since the 4Di can be upgraded to a Commander ecu.

Excellent! Now that I'm taking a good look at the GM HEI 8-pin setup, I'm liking it more and more. Looks like a good powerful, reliable, accurate system. I think I'll go with a matching hei coil, just to keep all the ignition parts the same-generation.

I wonder if there's a way to get the Ch*vy dist body hooked up with a Buick shaft, or so it'd drop into a Buick block...hmmm...not without cutting welding...prolly not. Hey, I've got a machinist friend, maybe he'd have an idea.

 

Actually, you'd be looking for a Buick lower distributor body and lower shaft cut 'n' pasted to a small-diameter Chevy upper shaft and upper body.

Seems very do-able to me IF YOU CARED ENOUGH. I wouldn't bother; splicing some wires and external mounting of the module would be satisfactory for me; and would eliminate the whole issue of aligning the cut 'n' welded pieces.

 

Yes, I have seen this done and it worked fine.

 

Looking under my hood this afternoon, I think I'll stick with the Buick distributor and mount the module either under the distributor body (like IgnitnionMan Dave does) or back on the firewall - maybe inside the now-unused voltage regulator box (I converted to internal-reg. alternator). Probably mount the coil in or near the stock coil location as well.

Now if I could only find a good, detailed wiring diagram for the Pro-Jection 4Di, the one in the kit isn't that helpful with the ignition. :rant:

 

Wayne,

How did your reluctor and rotor phasing go?

Any tips or data to speed along setup with the 8-pin HEI module?

Thanks,

ElectraJim

 

I used an odd fire v6 HEI body, then took the reluctor off an Olds V8 HEI and put it on the v6 shaft, pinned the mechanical advance, new V8 pickup coil, the whole 7-pin module assembly in the original 4-pin body. I didn't pin down the pickup coil so I had some adjustment on the trigger angle in the MegaSquirt software. I still haven't pinned the pickup coil, and after a few thousand miles on it, it hasn't moved..... But now I'm going for a crank trigger and going back to a points distributor with an MSD box. Ideally I'd find a 3.8L-4.1L seven pin distributor body, and an Olds' 7-pin reluctor, then v8 pickup coil, etc.

Base timing is set at 15* while cranking (and default if I loose the module), then MS2 controlled after cranking (I've taken it up to 65* advance as a test :eek2: to spot check the commanded timing vs. read on the balancer)

(I had a picture but it won't let me post it because my post count is low..)

 

Interesting. Buick spins the distributor clockwise, like Chevy and Cadillac. Olds spins counterclockwise same as Pontiac. I've never swapped reluctors between CW and CCW applications--I thought the reluctors were different; and would have screwed up the rotor phasing. Gonna have to check that out tomorrow.

'Course, rotor phasing also depends on how the pickup coil is positioned, too.