Jvette73

This is not a question on my vette but on one of my other Chevy powered vehicles. Since many other C3 vettes do use HEI I thought it a good idea to ask this here. im having an intermitent ignition(spark) failure that I believe is being caused by a faulty module. Heres the q's.

1. Are there better and worse quality modules available?

2. What are some brand names of good quality modules?

3. The distributor in the said vehicle is likely to have been swaped at some time in the past. Can I verify what year the dist is by looking at the number stamped on it?

4. What if any, are other problems that could be present that could lead to pre-mature failure of an otherwise good module?

Paul L

Go with GM, for the year and for the engine. Give me the number and I will tell you what that is.

page62

I'm pretty sure that car didn't originally have HEI. I think it was around '75 or so...

Paul L

I missed the obvious. Quite true; it was 1975. But the module should still match the distributor.

Jvette73

The vehicle in question is a 84 K5 Blazer. Ill get the #'s asap and post back. Thanks for the help so far. So will I need to go to a dealership for the GM module? The motor in the truck is a balanced 355 from a 70 Camaro. Its very smooth and idles real slow without the slightest stumble. Thats when its actually running with a good module. :D

Paul L

Or AC Delco outlet.

Pete79L82

All 8 cylinder Chevy HEI (non-computer controlled) distributor use the same module. The Delco # is D1906, The GM # is 10482820.

Jvette73

This dist in the truck has a second plug in harness comming from the other side that has at least 5 or 6 wires in it. Its probably a computor controlled model then huh? Although I do believe that the computor has been rendered inactive with all the parts swaps that have been done to this vehicle. As for all those other non-computor controlled models, you say they all use the same module. How many pins are on those modules. Im not totaly sure cause I havent yet removed my module, but I think mine has 2 pins on one end and 3 on the other for a total of 5. The original dist that was in the truck had no mechanical advance weights or vacuum can and was getting no spark advance. A long time ago I replaced it with the current unit that had the same harness plugs but does have the advance weights and vacuum advance. So as you can see with this melting pot of swaped in parts I really have no idea what year or vehicle this currently used dist is from. I will post back with the #'s when I get to it. Thanks again for the inputs

Ki m Le

Jvette73,
The HEI module with 4 pins is the machanical/vacuum advance design. The 5 pins module is the first generation computer controlled. The 7 pins module is the second generation. All computer controlled modules designed to have better gas milage and emission stuffs.

Since the system has been hacked, it's difficult to bring it back to the original setup. I would use the distributor without computer controlled unit from the junk yard, and make sure the carb is none computer junk either.

You will get a better trottle respond and performance out of it, but more gas and bad emission, if you don't have to worry about emission law.

Stick with GM HEI Module! As the fact, I'm running 4 pins HEI mod in my 68 with TI distributor for two years now, no problem!












[Modified by Ki m Le, 7:49 AM 12/20/2002]

Smokehouse69

Make sure when you replace the module, to apply heat sink grease under the new module. Heat is what usually kills HEI modules and the heat conductive grease will help dissipate the heat to the rest of the distributor.

Jvette73

Yes that is an option I have been exploring to switch to a non-computor controlled unit. If I find that the GM module I need for the current dist is expensive enough, it might be worth it to get a whole complete new dist from summit or jegs. Hmmmmm decisions decisions.... I might even have a 4 pin unit around here somewhere. Also, would it be possible to change the harness and convert the 5 pin unit to a 4 pin unit and toss the computor harness out? How about the summit HEI units? Are they reliable? Anyone using one? Anyway, what ever I decide Ill let you all know. Thanks everyone for all the help. :cheers:

Smokehouse69

Ki m Le,
It looks like from your picture that you have an HEI module hanging out of your TI distributor! I've heard of the conversion, but I've never seen how it was done. What did you have to change in the TI distributor in order to use the 4 pin HEI?

Ki m Le

Smokehouse69, this distributor is un-touch. All I did was to swap out the amp box with the HEI module and modified the wiring harness from the HEI distributor to match with the ign. Power/Gnd, dist and ign coil!

Jvette73, Swap out the HEI module and wiring harness is fine, but you also need the dist shaft with mechanical advance for the engine to run correctly!

Summit HEI? I never had one and don't know. I like to stick with GM's on Electronic parts.







[Modified by Ki m Le, 2:59 PM 1/3/2003]

mrvette

jvette, IT IS VERY DOUBTFUL the module is bad at all.....

I have found no differances among modules, as long as a brand name is on it....neihoff, napa, b/w....whoever....not some gypsey thing....'

NOW, the problem probably lies with the coils.....the spark coil in the cap has crimped wire ends on it....they need scraped and soldered...I have caught one of them pants down with open wire where corrosion/heat/whatever caused the quick cheap crimp over the formvar wire coating to loose connection....solder them both....red/wh/yel....any of them....

second off, the sending unit coil under the rotor assy....you have to see the two small green and white wires coming from it....need pull dist completely apart to change that damn coil....it's the FIRST thing in the housing after the bushing/bearings for the shaft....so gear comes off, snap rings next, then 3 screws usually 1/4 inch hex cap...then the coil is yours....finally....
they have been known to open up irratically...no pulse....

GENE

Jvette73

Update: I got to workin on it and broke one of the pick up coil wires right where it goes into the pickup. I hardly even pulled on it so it had to be ready to go anyway. Looks tough to fix so decided to remove and dis-assemble the dist to get a new pickup coil and module. Im glad I didnt buy those parts yet because the whole thing is muffed up now. Old coil, funky module, broken pickup coil wire, worn cap and rotor..yadayadayada. There was so much gunk built up on the inner shaft that is seems almost impossible to get the shaft out of the housing anyway. I drove it out and in the process the bushing was forced out on the housing. Anyhow, the solution is sitting in the box next to me right now. Its a new Summit Racing complete Non- computor controlled HEI ready to be dropped in. If this friggin rain would let up a bit Ill have it done in a snap. Again thanks to everyone for the all the help.

Jvette73

conclusion: I got the new summit HEI in yesterday and the truck is runnin smoother than ever. Its a nice dist although the mechanical advance curve is kinda short at only 14 degrees length. I just set the initial at 14BTDC at idle and hooked up the vacuum line and done. Its not a real performance setup anyway with a super low end cam making all its good power off idle to 4000rpm. Point A to point B, thats whats important with this one. Its doing that very well now. Thank again for all the help. :cheers:

72rdstr

1. Yes
2. MSD or Accel
3. Yes, google it
4. coil or bad voltage (high or low)
Todd