94 Wagon having electrical issues

[Chuckster61]

My 94 wagon started having intermittent cut-out engine quit problems. I noticed some weird buzzing and clicking under the hood with the ignition on and not running, and narrowed it to my fuel injectors. I just happened to wiggle the alternator connector, and found it related the buzzing injectors. When I disconnect the alternator connector, the problems stopped. Weird. Drove it home and started troubleshooting. This is what I did and got no fix:

 

Swapped alternator (thinking some kind of internal short) even though it was working. Tried to isolate a single wire problem from the alternator connector with no fix.

Swapped the ECU (four yellow connectors and located under the left drivers knee panel) no fix.

 

Inspected the main engine harness connectors. No apparent problems.

 

Now I’m confused by the Haynes manual referring to the MPFI and the ECU and wondering if they’re separate units? It’s as though the ECU/MPFI are acting as though the car was running when it just has the ignition on. I even noticed a pop and the engine rotate without going to ‘start’. (Like it’s getting fuel and ignition)

I’m stumped. Any tips would be appreciated

[Chuckster61]

Update on troubleshooting: I thought a faulty cam or crank sensor might be a cause, so I inspected them and disconnected them. No fix. I also disconnected the coil pack. No fix. The problem exists with the ignition “on”. And another thing, the tach jumps around in harmony with the clicking.

[doublechaz]

That sounds familiar like there was a similar thread here once...

[Chuckster61]

Update on troubleshooting. I decided to wring out the wires from the alternator. The charging wiring diagram shows a yellow wire that has a diode somewhere, routes to the ignition coil, fuse, and finally the ignition switch. I noticed the engine control diagram also shows the continuation of that wire from the charging system, and feeds back to the MPFI/ECU. To confirm the MPFI input, I connected my ohmmeter from the alternator yellow to the MPFI yellow, and had continuity. I'm going to disconnect it at the alternator connector.

Placed two jumpers to the alternator for the white and black wires. The car seems to start, run, and charge the battery!!! Don’t know why, but I’ll take it.

[doublechaz]

Something wrong with that diode? Bad socket if it is in a socket, or the diode itself maybe.

[Chuckster61]

Update on troubleshooting: I realized I had incorrectly jumpered the alternator wires, I had put the black/white wire to the yellow position. The charging actually occurred, but the original problem persisted. Turns out I need to power the alternator yellow connection and keep the black/white connection for the dash light. I got an alternator connector from the wrecking yard, jumpered the white and black/white wire, and powered the yellow connection via the A/C fuse. I used a ‘new circuit’ adapter and added a 15A fuse for the new yellow connection. All of the original symptoms have gone away! Problem solved by creating a new circuit which bypassed the ignition/diode circuit. None of the original harness was disturbed.