Ok, need a little help here troubleshooting a no-crank issue with a SBC.  Buddy of mine dropped a mid-80s 350 in a Jeep YJ, full carb setup with HEI ignition.  Jeep was running fine, but completely died on him the other day while driving.  He hasn't been able to get the engine to fire, and all it simply does is crank over.  We've verified fuel to the carb, but spark has been an issue.  We pulled a plug today and grounded it to the frame, and only get a very weak, intermittent (if any) spark.  We are assuming the coil pack has gone bad, but not sure.  What is the best way to go about testing the coil pack?  Any other potential issues that may be the culprit?

Just get a new coil pack

and curse GM for putting the rotor at the fucking back

have a nice scar from a 454 distib post through my left hand

fucking cap and rotor at the back

Hate to state a simple thing but did you take the distributor cap off to check for cracks or dirty contacts?

Make sure all your connections are good, pull the electronic module below the rotor and get it checked

Cracked distributor?? Had that happen on a ford with the same symptoms. Not the cap but the actual distributor. Good luck!!!

You are trouble shooting a "Crank- no start" not a "no crank".
Pull the spark plug wire off any plug.
Stick a screwdriver in the end
Hold it 5/16" away from any ground.
have an assistant crank the engine at least 2 revolutions.
Does it have spark or not?

If no-
Use a test light hooked up to a ground to check for power at the coil during "key on" and "cranking"
Use a test light hooked to power to check for dwell signal at the coil negative terminal during cranking.
The test light should dimly blink.

If you have both of these, but no spark- you need a coil or your cap and rotor is trashed.
If you do not have dwell signal- either the ignition module is bad, or the pick up coil is bad. Buy a complete rebuilt distributor- its cheaper than guessing and getting it wrong.

Chevy small blocks 101.
ETA: sorry, that sounded kind of arrogant. Good luck OP. I always kept a spare complete distributor in my truck (if it was chevy HEI or Ford thick film) when going into the desert or long distances.
ETA#2: If you use a jumper wire and briefly jump the coil's negative terminal to ground (while the key is on, or the coil is otherwise powered up) you will get spark out of the coil if it is good.

"Coil pack"? Is it a coil in cap HEI? One of those MySparkDied small cap HEIs with an external coil? Need further info to diagnose properly.

The last time I had problem with a chevy SB was due to the prior owner replacing a distributor and noyt indexing it to TDC

make sure you establish TDC and avoid "better" components delco plugs wires distrib = no worries

plain old copper

something catastrophically failed in the ignition.  It would still fire up with a couple cylinders down.  So you probably have a bad coil or adjacent controls.  if everything else is good and hasn't moved out of timing.  Can you turn the distributor with your hand?  Did the fork holding the distributor in place loosen up.

JFC, guy swaps engine and doesn't know the very basics of the most popular motor ever.

"Coil pack" probably isn't the correct term, and I believe its as you described (coil in the cap).  I know its not an external coil, as we had to pull the top of the distributor cap to remove.

I like the small cap HEI better- easier to diagnose a bad coil when you dont have to remove it. They seem just as reliable- if not more so.
OP, you probably have a bad ignition module if indeed you have no spark.
ETA: the module is the doohickey mounted under the rotor with 2 connetors on it.

Google "Chevy HEI coil Ohm test"

Check cap and rotor first then move on to other possible causes.

On most chevy trucks where the darn cap is buried and you can never find the right length screwdriver to get it off, its easy to check for power and ground first. Also, logically, its step one- verify inputs and outputs.

I had a "Pickup coil" go bad once on my old 85 GMC. Not a super common problem like the actual coil failing, but it happens. Drove me nuts for a couple of hours. I had it tested at an auto parts store, but that was back in the 90s.








 

most likely it is the pickup coil..since it does spark some..they tend to break the wire in the pigtail that comes out of the PC and connects to the ignition module..if it is, easiest way to fix it is replace the whole distributor(gotta pull the distributor to change the pickup coil anyway)and it will be the cheapest as remaned dist includes the ignition module as well.. make sure you know how to change a distributor before you pull it(its timed to the motor)...easy job if you pay attention.......

Billet HEI complete distributors are about $45 on Amazon and Ebay.  I am running three of them in different vehicles.

I am willing to bet the HEI module died.  They most likely look like the top 2 in this pic.

HEI distributors are easy as pie to diag and rebuild...new coil, pick-up and module cost you under 100 bucks...and a couple  of hours.

Completely forgot to update this thread...issue turned out to be a bad coil and ignition module.

This is my suspicion as well..  



rip it out and get an MSD 6A



 

It's your coil, low to no spark, easy fix.

Control module.