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Resolved Alternator Shot or Wiring Issue?

brandnew161

10+ Year Contributor
215
2
Mar 30, 2009
Horseheads, New_York
I've been working on this 2g for a few years now. I'll add some photos but essentially this car has been gutted. No longer using anything factory really. Just started the car a couple days ago and got it to idle fully warmed up today pretty well. I logged the battery voltage since I assumed my aftermarket gauge was faulty. Appears voltage is dropping and the alternator is not charging the Optima red top.

The only wire connection I have going to the alternator is a power cable. The cable goes to a fuse block then to a Quickcar 3 terminal battery disconnect and then to my battery.

I assumed that the alternator would be supplying voltage automatically via the accessory belt. Is one of the wires in the factory harness required to be pinned to the ecu to tell the alternator to "turn on"?

This is a factory 2g alternator that's been relocated. (Dont mind the wiring, work in progress!) Thanks

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steve

DSM Wiseman
14,717
1,587
Feb 3, 2002
Boulder, Colorado
You need to provide energizing field current to start the alternator working. That's provided on a stock car by the the alternator light in the cluster or by the alternator "relay" (they are in parallel). You may also need to do something with the sense and the ECU controls of the alternator that exist on a 2G.

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According to the 2G DTM the FR Terminal of the generator inputs the ON/OFF state of the generator field coil to the engine control module. In response to this signal, the engine control module senses the generator output current, and drives the ISC servo according to the output current (electric load). This prevents a change in idling speed that may otherwise be caused by the electric load.

* The generator generates power when the power transistor in the voltage regulator is caused to be ON to supply a current (field current) to the field coil. When the power transistor is caused to be OFF, the power generated by the generator rapidly decreases. The size of the generator output current, therefore, depends on the ratio that the power transistor is ON (ON duty).

The Engine control module voltage at FR terminal is low when the power transistor is ON, and high when the power transistor is OFF. Therefore, the ON duty of the power transistor in the voltage regulator or the generator output current can be sensed by calculating the ratio that the voltage at FR terminal is low. When the generator output voltage reaches the regulated voltage (approx. 14.4V), the voltage regulator switches the power transistor from ON to OFF. When the output voltage falls below the regulated voltage, the voltage regulator switches the power transistor from OFF to ON. In this manner, the generator output voltage is maintained constant.

The engine control module limits the generator output current by duty control of the continuity between generator G terminal and ground. When there is no continuity between generator G terminal and ground (let this be 100% duty), transistor No. 1 (TR1) stays in the always ON state. When the voltage at generator terminal S reaches 14.4 V, the power transistor is forced to OFF to adjust the generator output voltage to 14.4 V. This operation is the same as that of the conventional generator.
 
Last edited:

brandnew161

10+ Year Contributor
215
2
Mar 30, 2009
Horseheads, New_York
Thank you steve!! I know what I need to do now. I remember having difficulty deciphering what those pins on the ECU were for (33 &41). Thankfully I've saved all the harnesses for that Alt plug. And I am assuming that the 'power transistor' being spoken of in your post is the same power transistor/PTU located near the coil pack on the factory manifold?

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