Correct voltage from alternator?

[bmdubya1198]

After almost a week without issues, my V70 decided to start this rough idle again. This time while at an intersection, it had a hiccup or two, but everything else was normal.
After a couple minutes, my radio cut off for a second or two, and I noticed a real quick flash of what I'm almost 100% sure was my ABS light. I'm not totally sure because it looked like it was in that position, but it looked like a red light. Although it was a quick flash, like a fraction of a second.
This radio thing has been going on the past couple weeks now, where it will randomly shut off, when within 2-3 seconds it'll come back on exactly as it was before.
So once I got home, I was going to check the battery voltage but that just wasn't good enough for the car, so as soon as I pull the hood release, the cable snapped.
After getting the hood opened, the battery showed around 12.7 volts, perfectly acceptable.
Started the car, all accessories off it read ~13.67. With A/C on full blast, radio on, headlights and front/rear fog lights on, it read around 13.27-13.28 (though it was jumping around some, at its lowest it was 13.23). This was at idle, I didn't test it with the RPM raised at all.
Does that seem low? Maybe this has been my issue with the idle all this time. I'm really hoping this isn't a wiring thing.

[volvooh]

I have three 70 series volvos. They all get 13.6 to 13.8 off of the alternator. So it sounds based on my experience you are in the ballpark but others may chime in with additional insights.

Check your grounds, especially the ground straps from the back of your engine to the frame. I had an S70 that had the ground straps rotted off and caused all kinds of electrical problems including properly charging the battery.

[misha]

With ALL accessories OFF you should have 14-14.4v at idle.
With headlights,radio,heating and rear defroster ON you should have 13.5-14V at idle on healthy charging system.
Everything below 13.5v at idle is not enough to keep the battery properly charged.

You get those readings at battery terminals,right?
What are the readings directly at alternator(negative probe on alternator housing and positive probe at b+)?

If you have correct readings directly on alternator but lower on battery terminals,your positive battery cable is bad(the one from battery to starter or starter to alternator).Ground cable(negative cable)almost never go bad.

You should perform a voltage drop test:

alternator and regulator.pdf

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[bmdubya1198]

With ALL accessories OFF you should have 14-14.4v at idle.
With headlights,radio,heating and rear defroster ON you should have 13.5-14V at idle on healthy charging system.
Everything below 13.5v at idle is not enough to keep the battery properly charged.

You get those readings at battery terminals,right?
What are the readings directly at alternator(negative probe on alternator housing and positive probe at b+)?

If you have correct readings directly on alternator but lower on battery terminals,your positive battery cable is bad(the one from battery to starter or starter to alternator).Ground cable(negative cable)almost never go bad.

You should perform a voltage drop test:
alternator and regulator.pdf

Correct, those readings were taken at the battery terminals.
I have not tested voltage directly at the alternator, but I can do that tomorrow. Thanks for the PDF!

I also decided to check out the grounds. The ones that I could find are good. However, there are two grounds I would like to check out, and I can't find them. 31/50, which is located somewhere near the main fuse box, and 31/7, which is located on the a-pillar. I can't for the life of me find either one. I checked both areas very thoroughly and it appears they don't exist.

Also, this is possibly unrelated, but is a quiet buzz from the ignition coil normal? It also has some white residue on both the front and back, not sure if it's burned or just from water or coolant splattering it at some point.

[misha]

Main grounds are thick blue wires.One is behind driver's side headlight(between the headlight & battery) and the other one is down low at transmission housing.You can see it from under the hood...just follow the wire from negative battery terminal.

Other than that....you will have a two flexi wires(grounds)...one at passenger's side near the firewall and the other one behind upper torque mount,also near the firewall.

Don't worry about coil...it either works or not.

[bmdubya1198]

Good to know on the coil. I wasn't sure if that would cause an intermittent miss or if it would just fail.

The ground straps on the firewall are both good. I'll have to double check the one on the transmission.

I tested the alternator with the engine off, and I got 12.68 V, which is exactly the same as the battery. With the engine running, the alternator showed 13.92 V and the battery showed 13.82 V.
I also did the drop test exactly as that PDF said, and discovered a 0.42 V drop. I'm betting on the positive cable being bad.

[scot850]

Not sure if the 98 is the same as the 99-00 models but there is another ground on my car that is hidden between the air-box and the LH strut on the strut tower. If you look down you can see the bolt head.

Some cars have a flexi ground wire between the back of the middle of the block and a mounting point on the firewall to the right of the alarm horn. Last one is normally on the RH side of the cylinder head back corner and the inner fender area.

Neil.

[bmdubya1198]

Not sure if the 98 is the same as the 99-00 models but there is another ground on my car that is hidden between the air-box and the LH strut on the strut tower. If you look down you can see the bolt head.

Some cars have a flexi ground wire between the back of the middle of the block and a mounting point on the firewall to the right of the alarm horn. Last one is normally on the RH side of the cylinder head back corner and the inner fender area.

Neil.

Yeah, I saw that one on the strut tower. I retaped the larger wire just to be safe.
I'm pretty sure my car has 2 flex wires from the firewall to the cam cover. I just recently fixed the one near the right strut tower because the screw hole on the valve cover was stripped out.

[abscate]

I think you have two things going on, electrical radio problem and a different idle problem

Clean your IAC valve ( sneer) and are you stage zero on everything else?

The white residue is tears collected from the floor of the BMW parts counter.

[misha]

You just CAN'T test the alternator when engine is not running!
Voltage drop test must be performed after driving the car for about 30min and without turning the engine off prior to testing.
That way,the heat in the engine bay will show every hidden problem which will not show up on cold engine until the cables are heated up.