[GoGoat]

I have an aftermarket HEI distributor in my 69 Firebird. Seems like it goes thru a couple modules every year. I drive accross town and no start. change module and then starts and maybe goes 3-6 months. Is there a good brand out there I should be using? The original one lasted 4-5 years then this ongoing problem. Or should I look at the coil or replacing distributor. I added an extra ground into the base of the distributor. I cleaned and reinstalled all ground straps also. Thanks for any input.

[78w72]

best HEI module is a factory original GM unit. probably still able to find some in junkyards for a few bucks, i have a bunch of them i pulled from junk cars over the years. a GM module will outlast any aftermarket china crap module. when i had member "suntuned" rebuild an HEI a few years ago i sent him a few GM modules to test & they all tested good to 8000+ rpms. in 30+ years of owning HEI pontiac cars i have never had a GM module die.

grounds are good to check but also confirm you have proper running voltage to the dist. older cars that didnt have HEI usually had lower volts or smaller gauge power wire that wont work reliably on a newer HEI.

[george kujanski]

The pickup coil wires may also fracture over time due to the vacuum can rotating the pickup constantly. replacing the module also moves the wires so if they are defective, the process may temporarily fix the issue, rinse and repeat.

George

["QUICK-SILVER"]

Did that distributor come with a, low resistance, high powered coil?

Clay

[25stevem]

How much voltage is the Alternaor putting back into the battery at rpm's above 2500?

Also the gauge of wire that was used to bring voltage to the stock points type coil wil be encifient to carry the current needed to power a HEI.

The same poor current transfer could be taking place in the system where you crimped on connectors that now are not gripping the wire good enough.

[Half-Inch Stud]

HEI:

Be sure a copper wire from the fuseblock feeds the HEI. Stock 64-72 has a nickel steel resistance wire.
Be sure the center button is a 3 Ohm item, not a 6000Ohm button.
4-Pin GM Module works best, but after market modules mostly work well : check dwell vs rpm to see dwell change with off-idle-to-3000 rpm. if dwell walks with rpm then you got a proper module.

Use Cap with Brass tabs in Cap, not aluminum.
Wire can be just about any8 mm silicone, and most 7mm silicone. measure resistance to be < 25K Ohm for good performance and reliability.
gap plugs at .040-.045"

Ground wire from HEI base to head is a very good upgrade.

[Cliff R]

The factory "990" modules are excellent as are factory coils. I've never had any success whatsoever with aftermarket modules. Some work fine, but they ALWAYS fail sooner or later and I found myself going back to a factory used 990 module.

Right on the dyno I back to back tested my stock Pontiac HEI against an MSD billet distributor with a 6AL box. The dyno sheets were very close but showed a slight power improvement using the HEI. I attested this to the more accurate "knife" edges on the pick-up vs the wide style on the MSD.......

[Bermuda Blue]

Heat sink paste (not grease or rtv) must be spread thinly across the bottom of the module prior to installation or it will overheat and fail prematurely.

Make sure the mount surface on the distributor is smooth and flat for good heat transfer.

[Half-Inch Stud]

Originally Posted by Cliff R

The factory "990" modules are excellent as are factory coils.........on the dyno I back to back tested my stock Pontiac HEI against an MSD billet distributor with a 6AL box. The dyno sheets were very close but showed a slight power improvement using the HEI.......

I attribute HEI performance advantage to the variable dwell which enables to Coil to deliver high energy sparkings across rpm.

magnetic coil over-saturation from Points or fixed dwell cannot deliver such high-energy vs rpm.

[Schurkey]

The usual cause of repeat module failures is a defective ignition coil.

The ignition coil internal insulation fails, the windings short-circuit. The output voltage drops, the resistance drops, current draw increases, and overloads the module circuitry. The engine may run just fine with a wounded coil; at least under light or moderate load, and until the module can't take it any more.

One module fails, replace the module. Module fails again, you'd better test the ignition coil. An ohmmeter can tell you if a coil is defective. It cannot tell you that a coil is "good". However, if a coil passes all the usual ohmmeter tests (primary resistance, secondary resistance, primary-to-ground, and secondary-to-ground, and on most HEI coil-in-cap coils, primary to secondary isolation) AND does not have obvious carbon-tracking on the exterior plastic around the terminals, AND will fire a spark-tester calibrated for HEI, the coil is most-likely good.

Given the state of the "performance industry", a person is generally better-off to go ignition shopping at the Treasure Yard than at the Speed Shop. High-failure Communist Chinese coils are epidemic.

I'm not saying that the only cause of module failure is the ignition coil. Insufficient supply voltage, and the pickup coil has already been covered--although broken pickup coil wires are not the only way the pickup coil can fail and cause module problems. HIS has touched on the magic of variable dwell; and that's accomplished in the module and pickup coil interaction. Both parts have to work right for the variable dwell to work right.