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Old 06-07-2005, 08:37 AM
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HEI Woes

Hi all,

I've been a Ford guy all my life but have recently taken on a Pontiac project. I've gotten a 79 T_Top Trans Am with a 301 4v. The engine was missing on 2 or 3 cylinders when I drove it home so I figured a tune up was in order. I've replaced spark plugs (gapped at 60), plug wires, dist. cap, coil, rotor, dist. module and pick up/trigger coil. I even went to a salvage yard and picked up another distributor. My problem is that I still have 1 or 2 plugs that wont fire consistently. They don't even want to fire outside the compression chamber while holding them grounded to the motor. I place a timing light on all eight plug wires individually and some fires regularly and at least three are consistently missing. By placing pressure on the distributor cap towards the drivers side I can make the problem worse. While pulling the cap towards the passenger side the missing will tend to go away. As soon as you turn loose of the cap the problem begins to return. This occurs to two caps. With the distributor out, there seems to be little or no movement of the cap on the distributor mounting plate. This problem has me baffled. All I ever hear about the HEI distributor is how good they work and trouble free they are. I regapped the plugs down from the spec of 60 down to 50. There may have been an improvement but at least one plug still consistantly misses. Is the stock HEI coil capable of firing a plug gapped at 60? Do I need to regap the plugs down to maybe 45 or 40? I'm at a loss. I work with electronics and computers every day and stumped. I plan on pulling the motor for a stock rebuild but would like to solve this little problem first. Any help would be appreciated.


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Old 06-07-2005, 01:15 PM
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You may have gotten a bad distributor from the salvage yard.DUI recomemends a gap of .050 to .060 on their high aoutput HEI distributor. All HEI's I have used in stock trim were running a gap of .045.
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Old 06-07-2005, 04:07 PM
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Testing HEI

Doc here,

I have always run mid 70's to mid / late 80's plugs and HEI at 45 and never had a problem with it.

I would First Check the Cap, BE sure it is right for the dizzy...slight differences in the tower width can occur, even though the cap fits on properly..

If the PN checks to the dizzy (which MAY not be the PN for the car), Then pull the module, take it to the auto parts store and have it checked several times to "Heat" it up...If it fails...get a new one, and have it also checked before you leave the store...(about 1 in 5 new are bad...) When you re~install either module, Don't forget the heat sink compound or it will soon die..Be sure all the module wires are making good connection, not shorting or chafed or intermittent before calling it all good...

If the problem still exists, then test or replace the mag pickup inside the dizzy..It may be going intermittant...and this will be hard to test from ohm readings alone...so I suggest replacing it..Before you do inspect the magnet (star Cam) to be sure you don't have filings stuck to it..this will give "False triggers" You have to pull the distributer and disassemble the drive gear to get the mag pickup out...

Also inspect the cap for carbon traces slung around between the towers..however, with 2 caps tried, I should think this is remote.

You first EASY test is try a re gap at 45...

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