GM HEI Ignition Conversion

Introduction

This conversion replaces the factory computer-controlled ignition with a simple standalone system using mechanical and vacuum advance. Replacing the Ford 2.8L TFI ignition with a Duraspark ignition is a common conversion. The main advantage of using a GM HEI module over the Ford Duraspark is its extreme simplicity and compact design. While both are reliable electronic ignitions, the HEI is a “one-component” solution that is significantly easier to wire and hide in a clean engine bay.

Parts Needed

4-Pin HEI Module for a 1974-1987 Chevy Camaro

GM Aluminum Heat Sink

2.8L Duraspark distributor for a 1975–1979 Ford Pinto or 1975–1978 Mustang II 2.8L

Key Advantages of GM HEI

Integrated Design: The HEI module is small enough to be mounted directly inside the distributor or on a small external heat sink, whereas the Duraspark requires a large external box.

Simple Wiring: HEI typically only requires one “hot” 12V wire to run. Duraspark involves a multi-wire harness between the distributor, module, and coil.

Better Dwell Control: The HEI module is often cited for having slightly better electronic dwell control across the RPM range compared to the older Duraspark design.

No Ballast Resistor: HEI runs on a full 12V, eliminating the need for the resistor wire or ballast resistor often found in older Ford ignition circuits.

Availability: You can find a replacement GM 4-pin HEI module at virtually any auto parts store in North America for a very low price

Heat Disadvantage

The biggest “con” of the GM HEI module is heat sensitivity. Because it is so compact, it must be mounted on a flat aluminum surface with plenty of heat sink grease (thermal paste). If you mount it directly to a hot engine surface without a heat sink, it will “self-cook” and fail prematurely.

You should consider using a GM Genuine Parts 10474610 Ignition Control Module Heat Sink to mount your HEI ignition module to.

Engine Prep

Find TDC: Set the engine to Top Dead Center (TDC) on the compression stroke of cylinder #1.

Mark Position: Note exactly where the current rotor is pointing before pulling the old distributor.

Remove Old Unit: Unplug the wires, remove the 13mm hold-down bolt at the back of the manifold, and lift the old distributor out.

Duraspark Distributor Installation

Drop-In New Distributor: Align the rotor with your previous mark. As the gears mesh, the rotor will rotate slightly.

Seat the Oil Pump: If the distributor won’t seat fully, the oil pump drive hex shaft is likely misaligned. Slightly bump the starter or turn the crank by hand until it drops.

Install Cap: Once seated, put on the cap and ensure you have enough physical clearance from the firewall and air cleaner.

Wiring The HEI Ignition Module

The wiring is fairly simple. The GM HEI module has four terminals labeled:

W = Input Signal Negative

G = Input Signal Positive

C = Ignition Coil Negative (-)

B = Battery Positive (12V Key On)

The Orange (sometimes appears yellow) wire on the Duraspark distributor connects to the ‘W’ terminal.

The Purple wire on the Duraspark distributor connects to the ‘G’ terminal.

The Green wire from your ignition coil will connect to the ‘C’ terminal.

The Red / Green wire (12V Key On) that goes to the positive (+) side of your coil will get spliced and connect to both the coil and the ‘B’ terminal.

IMPORTANT: Make sure the wire has 12V when the key is in both the ‘Start’ and ‘Run’ positions. On the 1985 Ford Ranger there are two plugs on the driver’s inner fender that have a Red Wire / Lt Blue wire. This is the starting circuit (power in key ‘Start’ position) and need to be wired together. If you do an ignition conversion and the engine doesn’t turn over, the problem is most likely in the Red / Lt Blue wire. Also, your original connector may have a Brown / Pink wire that connected into the same terminal as your Red / Green wire. The Brown / Pink wire has 12V ONLY when key is in ‘Start’ position. The Red / Green wire has 12V when the key is ‘On’. They would both need to connect to the ‘B’ terminal on the HEI module and the (+) on the coil.

See the diagram below.

Grounds

The remaining Black wire on the Duraspark distributor will go to ground.

The HEI module must have a solid ground through its mounting surface. It should be mounted to a clean, bare aluminum heat sink with thermal paste. For best reliability, run a dedicated ground wire from the heat sink to the engine block.

CAUTION: Double-check all wiring before applying power. Incorrect wiring can damage the HEI module instantly.

Other Diagrams

1983 – 1988 Ford Ranger / Bronco II Ignition Diagrams #1

1985 Ford Ranger / Bronco II Ignition Diagram #2 (PDF)

1979 Ford Duraspark Ignition Diagrams (PDF)

Carburetor

Your 2.8L will run with the feedback carb, but not well. I would replace it with a carburetor from a 1975-1978 Ford Mustang II / Pinto 2.8L V6. If your 2.8 is more performance oriented, or has headers and upgraded exhaust, you may want to use the 350CFM Holley 0-7448SA 2BBL carb. This carb comes jetted for a V8. A good jet size to start tuning a 2.8 with is #54 jets.

Fire It Up & Set Timing

Start engine

Set base timing (~8–12° BTDC to start)

Adjust for best performance

Removing The Old Harness

You can remove the old harness that went to the TFI module on the old distributor if you want. I would make sure that the engine and charging system is starting, running, and charging properly before doing so.

Additional Cooling

TRS Forum Staff Member ‘alwaysfloored’ did a similar conversion in a Ford Pinto and mounted a 12V cooling fan that he salvaged out of a computer over his HEI module. You can get one cheap from Amazon.

Troubleshooting

No Spark?

Check:

• 12V at B and coil +
• Good ground on module
• Pickup wires connected

Backfires / Runs Rough?

• Swap W and G wires

Starts But Dies When Cranking Stops?

• Wrong ignition source (no power in START)
• See the ‘IMPORTANT’ note under wiring

Related Articles

2.8L Duraspark Conversion

Powerspark Ignition Conversion

Ford Ranger / Bronco II 2.8L V6 Engines

2.8L Chevy TBI Swap on to Ford 2.8

Ford EEC-IV/TFI-IV Electronic Engine Control Troubleshooting