Strange electrical problem

[diso12der]

Ok, first off, I have been a lurker of these forums for quite a while now. I have already searched numerous threads for an answer, but I can't seem to find it.

I have a 1997 GST, lightly modded.

K&N Filter w/ dejon pipe
Greddy Type-S BOV
Profec B Spec II Boost Controller

In any case, I've had a low voltage problem ever since I've had the car, but as of late, it's been getting worse. At idle, with some accessories on, the voltage would drop to the low 12's or high 11's.

At first I thought it was battery, but that checked out fine. I then replaced the alternator and put in a 135 Amp one from 4alterstart. I thought that would solve the problem, but there was no noticeable change, and in fact, the voltage seems to be worse now. (Low 12's at idle with all accessories and headlights off).

I checked my fuses and they seem to be fine, and I measured the voltage between the alternator outputs and the battery, and that seems to check out ok.

Could there be something else that's causing this? Bad ECU? Bad sensor?

I have one reoccuring P1400 code on my car (differential pressure manifold sensor), but could this have an effect on voltage levels?

This problem only occurs at idle. At anything above 1500 RPM, the voltage is fine. (about 14.0+)

Has anyone ever encountered this problem, or have any idea what else could be wrong?

Thank you very much.

 

[nutshot]

What are the symptoms? Are you gauging this solely off the factory gauge? How did you test the battery? How clean are the connections at the battery? Do you have any aftermarket lights, stereo or accessories?

 

[diso12der]

Oh, I'm basing this off my own voltmeter that comes with my turbo timer. I also used a multimeter on the battery to double check the voltage.

Not much in terms of aftermarket audio. I have an Infinity Basslink system, a boost gauge, and that's about it.

The boost gauge, basslink system, TT, and boost controller are really the only things that are drawing extra current from the alternator.

In terms of the battery, I even tried isolating it from the system by totally disconnecting it and jumping the car with a jump pack and then looking at the voltage.

Battery connectors are fairly clean.

Basically the symptoms are:

At idle, there just doesn't seem to be enough juice generated by the alternator.

It normally stays at low 12 or high 11, and after a while, the ABS light will pop on and the car will stall out moments later.

Like I said, brand new alternator, just installed a few days ago as well. 135 Amp version.

Thanks again.

 

[nutshot]

So, even with the battery isolated the car is stalling and dying? I give, this stumps me.

 

[diso12der]

Exactly. I have no idea what this can be. Maybe the ECM, or bad sensor?

 

[psychlow]

My guess is that you have a positive wire grounding out somewhere on the chassis......

Just a guess though.

 

[nutshot]

My guess is that you have a positive wire grounding out somewhere on the chassis......

Just a guess though.

I would think that would not be affected by engine speed...