Thread: Voltage Problem

So I wasn't sure if I should post this here or in Electronics, but here's the deal:

About 6 months ago I upgraded to a b15 alt when the old (17 year old) stock alt desided to die on me. A few days ago the idle started and go low, real low. Like 600-500 low and my vacuum drop to like 14inHg @ idle. I blame this all on the fact that my voltage started sitting at 10.9... pretty much all the damn time. Sometimes the battery light slowly dims then goes out.

So, question is, what should I check? Not to mindly of this subject field. I know bad voltage can cause all the idle problems, so I'm not worried about that. What should I check and how to fix what? I was thinking just go get a new battery, but I wanted to ask you guys first before I just start buying crap to try and fix something blindly.

Oh, and for the record: I am running a SAFC, Boost controller, and wideband off the ECU power supply. That might be doing it too... for all I know.

Is that the voltage at the battery or on the gauge. Check voltage with the car off at the battery and then with the car running. If it does not go to ~14V when running the Alt could be bad. The battery will at least see the voltage but may not be taking a charge if it was bad. If the battery is at 12V with the car off it should be good.

At the gauge while car is on (which is measured from the ECU power supply): 10.9v
At gauge while ingnition is to "on" but car is off: 11.9v

At the battery while car is on: 12.3v
At battery while ingntion is to "on" but car off: 12.3
At battery while car is off: 12.3v

So I'm taking it the alt is bad? Damn that sucks, where can I take it to get respun? At least it's keeping the car alive for now.

It does sound like a bat alt, it should take it up to ~14V with the car running. Take it in to get tested and double check all of your connections just to make sure.

were did you get the alty from?

Lame. I'll go take it to get checked out. At least it's keeping it high enough to crank for now.



I forgot the parts dealer, but it was from a wreaked b15. Looks to be in great shape. It's all clean and looked bearly used honestly, so it seemed to come from a good car that just got in a bad wreck.

A fully charged battery is around 12.7v under no load. Take it to advance or auto zone who can test both your battery and alternator on or off the car. It sounds like the alt has gone bad and the battery is the only thing left running the car. Best case, battery is chargable and you just need a new alt. Worst case... You may need both

For anyone that might care, here is what was wrong:



The + cable had broken away from the spade, so next to no leads were coming from the alt. Fix it all and now everything works right as rain.