New alternator, turn headlights idle drop and CEL. No actual CEL recorded.

ASSISTANCE Electrical & Entertainment Systems
1

Car is a 92 GSR.

Installed a remanufactured alternator (70A) from Advance Auto and started the car up, turned my headlights on and idle drops (but stablizes, may not be an issue) and the check engine light comes on.

I have jumped the connector and all I get is a solid CEL.

Turn the car all the way off, start it back up with no headlights or load, no CEL.

Have checked the battery at a full load test, 14.20V, and at a no load test, 14.4.

I do have a grounding kit system to the alternator casing so my next troubleshooting is to remove the grounding kit.

Let me know what you guys think it may be.

2

well, a solid cel points to an issue with the pcm. the pcm regulates alternator field strength through a reference voltage received from the ELD. judging by your description, it’s quite possible that the pcm is at fault.
you can test the eld, with engine running and all accessories off, by back probing the red/grn wire across the black wire. take note of the voltage output. now, turn the lights and accessories on. the voltage should have increased. if it stayed the same, or voltage is erratic, the eld is faulty. usually it would throw a code for it though. it sounds more like the pcm is the cause to me

3

Ditto the above ^^^, solid CEL = PCM problem. 94

4

Thanks guys, will definitely check what you two suggest.

Odd thing was is that with the old alternator a CEL did not come on with the lights.
(Should have stated I also have a PnP 35W HID Kit)

What " red/grn wire across black wire" are you referencing to?

5

Okay, so I did some research and looked at the schematics diagram in the HELMs.

Found that the ECM and Alternator are connected through these wires. 1-D blue, and 12-B (No clue where these wires are located)

SO, I figured maybe with the turning of the headlights on there would be, for a fraction of a second, insufficient power to the ECM and therefore cause a CEL to occur.

Dont know if thats the same thing as welfare suggested…

schematic 1.jpg
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6

the ecm provides power to the field windings through the blue wire. you can see the diode in the diagram indicating the direction of current.

strange that the old alt didn’t set off the cel. i kinda wanna say take it back and try another, as i’ve heard of aftermarket alts illuminating the batt light etc… but i know it’s a bit of a cunt to re&re. anyway that you can get a hold of a test ecm? cuz that would be easier to try. even just a p75 or obd1 pr4. just to see if it throws the ecm code still

7

Okay will try some troubleshooting today, checking my grounds and grounding kit, ecu plugs ,and with an auto Pr4 ecu.

Thanks for the help welfare.

NOTE: with all accessories on it will not cause a dip in idle or cause a CEL to come on but until I turn the headlight on it happens. I’m thinking its a headlight+power+alternator issue.