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· Registered
18 Posts
Discussion Starter · #1 ·
what are the signs of a failing HEI ignition module?

or is it: they work or they dont?

car is 76 vette w/ 350cid stock dist

my tach breaks up over 4000rpm
im going to replace the inline tach filter but
wanted to know if you can trouble shoot an ignition module before it fails ?


· Premium Member
6,794 Posts
i would yank the whole thing and get you a mallory performance HEI. I just put one in my (77) firebird and couldn't be happier. Why buy an aftermarket module, aftermaket coil, curve adjust kit and an adjustable vacuum advance along with a performance cap and coil when you can get them all for 150 bucks ON TOP of a brand- new, no slop BILLET distributor.

Best money I spent in a while. Looks cool too!

p.s. theres a pic of the thing in my photo gallery, click on the orange hemi pic under my name-


· Registered
761 Posts
Personally I think for most street applications the hei is the best choice and the aftermarket are kinda a waist of money. The hei gives as much voltage as you will ever need, is dead reliable and dirt cheap what more could you want

· Registered
7,716 Posts
HEI Repair

Doc here:pimp:

Your in-line filter will give you both Tach malfunction, and Miss-fire, On the newer Vettes 80 and up, CCC's And CCCC, will also throw codes and May or may not run Depending on how bad the Filter is.

If The Coil going out, or having dirt "Arc~Over"under the Coil Cap will also cause this.

Also insure your Tach is hooked up on the FILTER side, not the HEI side or you will Damage the Tach on the Vette. It is a "Buffer" or wave shaper for Tach and for Computer controlled Cars.

If you STAY with the stock HEI, The module , and If it is failing, USUALLY They Will start to malfunction under heat...The best thing to do is take it to the Auto parts store and test it, several times to heat it up...Don't forget lots of heat sink grease on the Module or new one when you replace it. But these usually are "It is" or "It Ain't" issues. Also the Cowl Cover over the Distributor Acts as a heat deflector, so don't forget to replace that when your done...You'll get more life out of the module.

Another malady, Is the Cap Rotor Button, Spraying Carbon all over the inside The Cap and rotor. Debris and moisture will also get into the coil well under the coil(This happened on my 78 Vette, Ran like Crap in a can until I cleaned it up with Electrical cleaner!) And Cause Shorting points at higher voltages.

IMO, Get a new module, Filter, and Clean or replace the inside of the Cap and Coil well. Replace the Carbon Rotor Contact and Boot. You may want to also replace the Coil at this point.

That should Fix the problem, If not, Replace the Wires with GOOD 8 MM or better spiral core wires...USE the Stock Wire runners that Corvette provides, these are also heat Shields. This is best done from Below.

Hope it Helps!

Doc :pimp:
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