Hi everyone
My Vette drove fine after replacing the old ignition module in the 77 HEI distributor.... but after driving about 100 km it won't start... Again!

I will replace the ignition coil (the only part I didn't replace). There are a lot of different ign. coils around (from $17 - 69$).
I prefer to buy this part on Amazon, but I can't find the original GM #1985473 or D530, so I'll need a subtitute part...

What would be a good choice? I found these:
- Walker Products 920-1003
- Standard Motor Products DR31

Maybe you guys have other recommendations?

 

MSD is another option.

 

I would be inclined to suspect the ignition module again. The quality of the parts we are getting these days is awful. It would not surprise me in the least that it had failed again. You did put the required grease under the module when you installed it?

 

Do you know the part number?

 

Yes I put the grease on the there (the proper way). The part was from AC Delco (box) and there was a 'GM' sticker on the module...
I can't believe it would be the ignition module again. Do you guys always have to replace the module after 100 km...

 

Ngk rockauto
https://www.rockauto.com/en/moreinfo...166832&jsn=295

dont throw away old module or coil..
new modules are sketchy imo..try ebay for module
make sure module has correct ‘grease’ for heat sink...

 

I'd be tempted to agree, it's usually the module rather than the coil.
FWIW, the MSD coil for a stock hei is the 5525.
If you are really smoking coils I'd try to see why, they don't like heat and running the stock shielding over top might be a concern, you could look at an external coil
M

 

Part Number: MSD-8225 This is the upgrade to the 5525.

 

Can a bad timing a carburetor tuning be the problem? (=>extra heat)

 

Control modules use heat sink paste that is thermally conductive, but some I've seen come with clear dielectric grease and that's not what they need.

HEI coils, there are two polarity types, red/yellow and red/white. Think my 77 C3 stock one was red/yellow. Not long ago I pulled the coil in the cap that I took off at 33k because I am gonna use my old C3 modded HEI in my project truck BUCK and wanted to buy an aftermarket in-cap coil. The stock coil still looked new. Only pulled the stock cap/coil because I went with an msd control module & external coil for awhile and then later put a total msd setup on my C3

MSD's HEI dist come with an external ground because most of their failures were due to alum intakes poor grounding as alum surface corrodes fast. The HEI grounds thru the housings contact with the intake, cam gear and oil pump none are ideal grounds. I've read of others having problems after installing an aftermarket coil or going thru multiple control modules and resolving it by adding a dedicated ground from the housing to the block as a poor ground increases resistance and heat. I'm sure it depends on your climate/weather/storage/use/vehicle age n so on to determine if your ground is sufficient.

Interesting side note, when I bought my 86 C4 with 89k, I drove it home with a melted cap, the coil bushing had fallen thru and it was on top of the rotor. Drove fine!

I could go on bout the HEI or ignition stuff(not that I'm an expert) but think I've already provided more than is needed LOL Prob just as mentioned the replacement module died.

edit: HEI housing also touches/grds thru the block where it passes thru but still oily and not ideal. Grounding points are usually fine for normal use but for performance wise it can be better.

 

Would an MSD ignition module be of better quality than the AC delco part?

 

Sad part is if you can find module out of a wrecking yard from the 70's it'll likely last forever, new ones seem almost hit and miss
M

 

The one I installed was years ago and was new old stock at the time, a green module. These days anything MSD is questionable, their current coils are known to fail, I had one die after 40 miles. I'm not a MSD fan these days but I have several of their ignition boxes since their pretty much the only game left in town.

OEM stuff was well made to last, much of the aftermarket isn't. They don't have the testing or massive bulk material buying to offset cost. I couldn't name any brand that is foolproof these days, just buy two and keep the tools needed to swap it out if it happens again. If that's the problem. Wish I had brought my old coil n some tools when I put the msd coil in.

 

My experience with MSD has been favourable. Several years ago I bought their HEI upgrade kit which included the module and a rev limiter function. Ran it for a few years with no issues. I now have the MSD programmable box and would never go back to weights and springs. Way too old technology for my liking.

 

Yes, heat can be an issue. What is your timing set to ? Can you measure your underhood temps or upper radiator hose with an IR thermometer?

A bad alternator can fry parts, too. Do you have a friend with an O-scope?

I'd still suspect the module first, but look for a reason why it is failing.

 

I just changed to an HEI on my ‘71. First thing I did after getting it running was ordered a spare coil and module from Rock Auto. I’ll make a little styrofoam box to carry them in the car.

 

As I recall, the modges were notorious for failing at 60,000M. GM knew that, but back then (1976) that was a lot of miles. That was getting close to junkyard mileage.
My '76 Monte Carlo made it to 61K before biting the dust. A ziplock bag of ice on the dizzy cap got me back home for a repair / modge swap.

 

I will replace the module (again) + install a new coil. I'm also going to check the timing and carb tuning.
Hopefully it was just bad luck...

 

Picked up an MSD coil.

 

You can check your old coil with a multi-meter to see if the ohms are within spec. I don't what the readings should be but you can google. Maybe the module can be tested also?