Cart only runs with Voltage Regulator green wire disconnected

[Uisce]

I've had a charging problem for a few years, so I replaced the voltage regulator. When I put the new regulator in, the starter would spin the engine, but it wouldn't fire. I confirmed that the problem was no spark at the plugs. I disconnected the green wire from the regulator to the DF post on the starter/generator, and it started just fine, but obviously can't charge.

With the start/gen on the bench and the A-F jumper wire removed, I have good continuity between A1 and A2, and between F1 and F2. I get 5.5 Ohms between the F posts and DF, which is apparently in-spec. There is no continuity from any post to the case, and the brushes and commutator are in good condition. With the start/gen in the cart and the DF post (green wire) grounded, the cart will crank but not fire (same symptom as connecting the green wire to the voltage regulator), where I would expect to see 17+ volts.

I have now swapped the starter/generator, the voltage regulator, and the solenoid from my neighbor's cart, with no change in behavior.

If I unplug the green wire from the voltage regulator, I get good spark and the engine runs (but obviously can't charge the battery). If I connect the green wire while the engine is already running, it continues to run, and I suddenly get 14+ volts at the battery, but as soon as it stops, it will not start again until I disconnect the green wire and start over.

I suppose that I could wire a toggle switch in the green voltage regulator wire, and flip it once the engine fires, but that doesn't resolve whatever it wrong with it.

I put the battery on a load tester, and it shows good, but I'm planning to swap the battery with a known-good one when I get home tonight.

I've done a lot of searching on testing voltage regulators and such, but I've never seen anyone say their cart would ONLY get spark and run if their green wire was disconnected.

Any help would be greatly appreciated!

[robmartinez]

Did you ever get this resolved?

[Uisce]

Originally Posted by robmartinez

Did you ever get this resolved?

Yes! Tonight in fact.

I swapped the coil and ignitor for a borrowed pre-MCI (all I had access to), and it really didn't like that. The timing was way off. I suspect the pre-MCI ignitor is expecting the negative pulse before the positive from the transducer (pulser coil). I only ran it that way for about 3 seconds, but it was enough to cause some pretty bad knocking. Great. I swapped the black and red wires from the transducer, and it ran better, but still not quite right. I didn't run it for long enough to check voltage at the battery, but it started with the voltage regulator green wire connected, which was a nice surprise.

I needed to give the borrowed parts back, so I put the MCI ignitor and coil back on, and the behavior was back to the original problem (crank but no fire with voltage reg connected).

The MCI ignitor is several hundred dollars (BU has them for $575!), so I went to AutoZone and picked up an HEI ignitor (part # DR100, about $25). I told them 1977 Blazer 350, but it was used for a ton of vehicles.

I wired the HEI terminal B to the D post on the solenoid (the small hot post), C to the white wire to the original MCI coil, and the red coil wire to the D (small hot) post on the solenoid. For the transducer, I ran W to the red wire and G to the black wire (HEI expects negative pulse first, also).

It started easily with everything connected, so I drove it around for a while. It runs just fine and I've got 14.5V at the battery while running. Problem solved for about 4% of the price of the factory ignitor. Just be sure that you mount the HEI module so that the metal plate on the back is in firm contact with something metal to use as a heat sink. I just drilled a couple of holes and bolted mine where the factory ignitor was.

I've seen that some people have issues with the HEI setup. I can't speak to that, but not all HEI modules put out the same voltage on the W terminal. The DR100 I have is about 1.4V, and it works nicely for me, so if you're looking to do the swap, I'd specify that part number. I also don't know how it works with pre-MCI or GM coils, but it works well with my original MCI coil. If you need to replace the coil, too, the C849 coil should be a good match for the DR100.