Need help with "Poor Man's HEI"

[Baskinator]

I've been trying to upgrade my ignition module with the GM 4-pin HEI module, written up by shaggimo here: http://forums.amceaglenest.com/index.php?topic=31827.0;all
and originally posted here:
http://www.junkyardgenius.com/ignition/jeep/HEI01.html

I used a junkyard stock GM module, which I bought immediately before finding them brand new on Autozone's website for $5 more, so I'm hoping that's not the culprit. Everything is wired up correctly according to these write-ups, and I have a very large aluminum heat sink (sourced from an Xbox 360 processor) attached with heat sink compound sandwiched in. I soldered the diode in correctly, trying to avoid heating it too much in the process, and wrapped the connections up. The only thing I haven't actually made yet is a bracket to bolt it in.

For a further reference point, I've been running well with the TFI upgrade for ~1000 miles, and recently bypassed the ballast resistor to install my new 3.0ohm Pertronix Flamethrower coil. It's been starting and running even better since. I do not know if the ECM Test has been performed, but it ran a feedback Carter originally and now has a non-feedback Carter, so I'm guessing it has.

Anyway, this is for my '82 SX/4 which has a third connector for timing control on the stock module. Of course, the HEI module doesn't control the timing, so this could possibly be a problem. When I connect everything (disconnecting that third connector) and go to start the engine, it struggles much more than the stock module to fire up. Once I can actually get it going, it loses a little bit of vacuum every few seconds for some reason and usually dies. I have a vacuum gauge attached to the manifold which shows the needle at "late on timing", no matter how I adjust the distributor. I've had it running well enough to drive, but it was scary when it almost died accelerating into a couple intersections, so I switched it back.

I haven't fine tuned the carb or timing together yet. They are probably off a little bit, but it runs well enough normally and I would think it would need adjusting after an upgrade like this anyway. Any thoughts? I especially love how this is plug and play, so I can just switch the old connectors back in a few seconds if need be.

[shaggimo]

It very well could be the module, some are picky believe it or not. One that works perfect in one car, may not work at all in another (experienced 1st hand, lol). Have any gm buddies that would let you test one they have or test yours in their distributor? Most places cannot test hei modules, but there are a few chain stores that can, advance maybe?

[captspillane]

My vaccuum gauge has those notes on it too, where it tells you in this range do this. Don't remotely trust that. It has nothing to do with what you should actually do. The only helpful indication I got from trying to use that while tuning is that the needle should be steady when you idle. If it bounces erratically there is a problem to be found. The problem isn't always timing or even fuel mixture like the words on the gauge imply. 

[Canoe]

If you're driving the HEI module from the distributor, then G and W get the wires from the disributor and ground goes to ground (if running rough, swap them). These wires need to be twisted to cancel/minimize interference from the high voltage wires.

If you're using the Eagle ECU, then G gets the signal from the ECU and W goes to ground.

I read to watch out as not all HEI modules have the same ground, as in: one or both of the round shafts through the module may not be connected to the ground of the module, which is expected through the base plate, which is also the heatsink surface. With all wires disconnected, use an ohm meter to check continuity between the ground plate and the through holes. Establish your ground as appropriate.

If the 12 VDC to the stock ignition module still gets 12 VDC when starting, then you don't need to vampire power from the Start signal through a diode (which will also cause a voltage drop to the IGM supply voltage). The diode prevents the normal 12 VDC IGM supply from causing a false Start signal to the ECU when running.

[Baskinator]

So I had the module tested at NAPA today and they told me it was still good. At least it ruled that out, and won't cost another $25.

Dave, I figured it wasn't extremely off or anything since the engine runs well normally with the gauge reading "late on timing". However, it does have a vacuum drop every couple seconds, maybe going from 18/19 down to 14/15 on the scale. It's weird because it's not always the same, sometimes it runs good for several seconds and then drops, while other times it will drop every two seconds and then die.

I'm assuming it's using the ECU, as I haven't touched the wires from the distributor, and followed those write-ups almost exactly. All the wires go into those two connectors, which I sourced from an old duraspark module.

I'll wait to remove the diode if necessary, but I don't know exactly how to test the voltage to module. I guess the "false start" signal wouldn't be a problem then without the diode, as long as it gets a full 12 volts? I'll admit, I don't know a ton about electrical systems.

How would you go about establishing the best ground from the module? I believe this is probably the culprit, or at least part of it.

[Canoe]

The writeups don't necesarily cover all eagle model years. Most are for jeeps.

My eagle supplies 12 VDC to both the IGM and the ECU from the same swtiched line. No point in pulling the start signal dropped down through a diode, as it already has 12 VDC.

My '86 only has three of the four wires of the x4 connector, so that leaves the W hanging with nothing. It has to be grounded if you're using the ECU, or it gets one of the distributor wires if you're bypassing the ecu.

You have to use an ohmeter to see what is grounded. See what I wrote above about grounding.

[Canoe]

...I'll wait to remove the diode if necessary, but I don't know exactly how to test the voltage to module. I guess the "false start" signal wouldn't be a problem then without the diode, as long as it gets a full 12 volts? I'll admit, I don't know a ton about electrical systems...

You don't remove the diode. You remove the whole connection to the "start" power.
You should only need the one power connection, the swtiched 12 VDC.
You can test easily: disconnect the wire to the starter (so it won't turn over the motor while you do this); with the ignition on, measure the voltage supplied to the IGM plug to find which one provides 12 VDC (you'll connect and power the HEI IGM to this 12 VDC); have someone turn the ignition to "Start" and you confirm that this same IGM plug connection still gets 12 VDC durning "Start". If it doesn't, THEN you need the second connection through the diode.

Consider doing this at the same time: ECM Test
http://forums.amceaglenest.com/index.php?topic=38916.0
make sure you twist the wires from the distributor so there's less interference from the high-tension wires.

[Baskinator]

I kind of cheated, I just tested it with the single power connection (four wire connector). Still nothing, wouldn't even start.

Wish I had looked at this earlier. I took a trip to the salvage yard today and got a spare Duraspark module, this time with all three connectors like my stock one. I would have grabbed the male connectors had I known about this version of the ECM Test.

It stinks that I got all this together and can't get it to work. I feel like I might just stick with the stock module for now, and I have a spare in case anything happens. Hopefully the HEI will work after I can get the ECM test done.

Luckily the car starts up pretty easily every time with the new Pertronix coil and resistor bypass.

[Canoe]

I kind of cheated, I just tested it with the single power connection (four wire connector). Still nothing, wouldn't even start.

Yeah. That wouldn't work.
The two wire connector is what powers the module. Without power...

[Baskinator]

I guess I misunderstood your explanation then. If in fact this is the problem, how would I keep the diode connection intact without actually removing it, and still retain the 2 wire connector? Would the ECM test solve this, or do you simply mean that I have to disconnect the white wire with the diode in it?

[Canoe]

Look at the diagrams. Take the time to understand them. Most are done for jeeps.

The two wire connector powers the IGM. The stock IGM stakes both and handles them internally. The ballast resister for the coil limits the current to the coil so it (and the stock IGM) doesn't burn out.

The HEI-IGM needs/takes a continious 12 VDC to power it, doesn't require a ballast resistor as it uses current limiting internally (you always have the highest coil voltage possible). It has a single power input connection. Depending on the wiring of the starting solinoid, you need either:
- the switched igntion VDC that powers the stock IGM and the ECU (available as one of the two wires in the two wire connector) - use this method if this connection is live with 12 VDC when both swtiched and "Starting",
- or, like some jeeps, you might also need the "start" feed (that's the "start" signal to the ECU that also bypasses the coil ballast resistor and provides the maximum available battery VDC to the coil while starting) to power the HEI-IGM when starting.

In the second case, as the HEI-IGM takes a single power input, you need to isolate the "Start" feed from the swtiched feed, so the switched feed 12 VDC doesn't appear as a false "Start" signal to the ECU. This isolation is acheived by the diode.

[ammachine390]

I guess I misunderstood your explanation then. If in fact this is the problem, how would I keep the diode connection intact without actually removing it, and still retain the 2 wire connector? Would the ECM test solve this, or do you simply mean that I have to disconnect the white wire with the diode in it?

Since yours in an 82 model, the wires from the distributor should plug directly into the ICM harness. But your original module had the third connector, if you just replace your ignition module with any regular non computerized ignition module, such as the HEI one you are trying to use, that should take the ECM out of the loop without doing any other wiring modifications.

[Baskinator]

So I looked back over the Jeep write ups, wiring diagram, and all the suggestions. Canoe, I saw what you meant and found the exact same suggestion on the Junkyard Genius page. Don't know how I missed that, but I pulled the white wire from the terminal and wrapped the end so it wouldn't contact anything.

I also somewhat understand how the ECM test eliminates the computer, taking a signal directly from the distributor. With my stock module, the computer advances distributor timing, but the HEI does not. I've noticed a clear difference when swapping between them that the distributor timing must be manually advanced for the HEI module.

However, the HEI module still has great difficulty starting even after timing adjustment, whereas the stock module starts instantly. I feel like this might be remedied with the ECM test. I still need to get the connectors from the junkyard, but it will probably be a while since I don't even have gas money. On the other hand, I noticed the HEI helps the engine run significantly better once it actually gets going. Can't wait to get it working correctly.

Thanks for all the help guys!