Alternator/battery problem?

[reddingcruiser]

I'm stumped. Everything was running fine, then gremlins attacked.

The 5.7 TBI won't run with alternator hooked up. Two wire alternator, if both are hooked up it will not start. Unhook either and it starts and runs fine (but won't charge, obviously).

It seem power spikes are shutting down the ECM, but I can't figure where it's coming from.

• New alternator has same condition.
• Have a spare ECM, same condition with either
• Battery grounded to engine, ECM grounded to engine, engine grounded to frame in two locations
• Checked solenoid
• Check engine light stays on with key on when running but no codes other than Code 12 (no faults)
• No arching when connecting/disconnecting battery, so assuming no shorts (at least external to battery)
• ECM and harness can be isolated from OEM harness by pulling fuses, engine ignition and starting circuits can operate separate with their own fuse panel. No difference either way.

I'm taking the battery out this morning and taking it to NAPA to test.

I hate automotive electrical systems!

 

[Curt]

Is the alternator and the voltage regulator in known working order?

 

[reddingcruiser]

Is the alternator and the voltage regulator in known working order?

New alternator fried. Literally been working with an electrical engineer (my neighbor) on this all day. Found a few issues but no smoking gun.

Alternator has internal regulator. We "rang out" every wire, found two loose connections but no dead shorts.

I had two fused wires on the FJ40 OEM fuse block that no longer serve any purpose on my rig so we removed them from the fuse block completely to limit possible issues.

I'll be headed to NAPA in the morning to pick up an alternator. I'm going to go to a one-wire alternator to eliminate one more circuit, a hopefully, the problem.

 

[honk]

Might be better to work on your truck while that engineer is at work.

 

[Curt]

If your running an internally regulated alternator have you bypassed the external regulator on firewall under master cylinder.

 

[reddingcruiser]

Might be better to work on your truck while that engineer is at work.

Nah, she has a vintage Camaro she plays with, so it's not her first rodeo.

 

[reddingcruiser]

If your running an internally regulated alternator have you bypassed the external regulator on firewall under master cylinder.

None of the OEM Toyota ignition is in play. Starting and charging are pretty much all GM. Exciter wire came from key--on fused power and power returned to battery.

Power enters the harness through the original white wire via the ammeter, or key through original light blue and red, or black and yellow.

Rubithon gremlins are in all-out attack.

 

[reddingcruiser]

I am still trying to resolve this problem. I've had two different ignition/ecm harnesses installed with the same result.

Completely removed the OEM Toyota harness with the same results.

Wired ECM direct to battery with the same results.

Now have a one-wire alternator, with the same results.

I'm trying rationalize how engine sensors could be affected and create these symptoms.

Some rocket scientist out there must have seen this before. Remember, this thing starts at the touch of the key and runs perfectly - without the alternator hooked up.