'69 to late model GM HEI
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,438
Likes: 2
From: Melrose Florida
'69 to late model GM HEI
I know this has been thrashed out comepletely, but a slightly different question:
Will a stock GM HEI unit with the 3-wire pigtail out of the bottom (computer?) work? What I don't know is if these wires control the spark generation/distribution in any way, or if they are just outputting information to a computer on a car so equipped.
I know all about the dedicated 12v to the coil, and the other coil wire can be used for an electronic tach.
If I can use a distributor w/this additional pigtail, do I need to do anything to the wires, or just leave them hanging.
Thanks in advance,
Steve
Will a stock GM HEI unit with the 3-wire pigtail out of the bottom (computer?) work? What I don't know is if these wires control the spark generation/distribution in any way, or if they are just outputting information to a computer on a car so equipped.
I know all about the dedicated 12v to the coil, and the other coil wire can be used for an electronic tach.
If I can use a distributor w/this additional pigtail, do I need to do anything to the wires, or just leave them hanging.
Thanks in advance,
Steve
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
If GM HEI has 3 wires out side at bottom ... it's not for computer ... that 3-wire pigtail plugs directly into large, coil-in-cap distributor cap. Your 12v power also plugs into cap at BAT+ terminal and a tach signal for ELECTRONIC tach exits cap at TACH terminal. As you probably know, standard plain jane GM HEI does not have crossgear/tachdrive to operate your 69's OE mechanical tachometer ... but some aftermarket HEI do have tachdrive for mech tach.
Thread Starter
Drifting
Joined: Feb 2005
Posts: 1,438
Likes: 2
From: Melrose Florida
Thanks, Jackson. The junkyard distributor had that pigtail flopping, so I thought that it went external.
Steve
I know I won't have mechanical tach drive, just trying to get running at this point.
Steve
I know I won't have mechanical tach drive, just trying to get running at this point.
Tech Contributor
Joined: Aug 1999
Posts: 14,382
Likes: 6,401
From: At my Bar drinking and wrenching in Lafayette Colorado
If the HEI you have has a vacuum advance control unit on it, it's not an ECM-controlled HEI. The 3-wire pigtail plugs into the cap. If there's no vacuum advance, it's an ECM unit, and should not be used without the ECM since the computer fully controls all advance functions.
