j.kenzie@sbcglobal.net

Hi Jason,
I believe Alan is trying to have you measure a voltage drop over the length of the ground strap, while connected and functioning normally. That voltage from one end to another should be very low, maybe 50 milivolts. If it is more, and especially if it varied with flexure, jiggling, etc., it casts suspicion on the integrity of the ground strap.
Good luck,
Dave

jwbeck17

Thank you for the clarification. I figured that is what Alan was going for, but I had one of the probes in the wrong position. I suspect that my revised stated probe positions (basically both ends of the ground strap) is the recommended approach to see if I get any activity.

Please let me know if I'm off here.

Will need to check tomorrow evening, as I have put the 928 to bed for the night and the exhaust is not neighbor friendly.

Alan

Yes exactly - tomorrow is good. Might be good to drive it for a bit until its warmed up if you don't see any issues on initial startup - however limit run time once it starts doing this for safetys sake...

Alan

jwbeck17

Got some readings. I let her idle for a while to get the temp up as the weather is not good for driving.

First, the battery reading at idle (both posts) was at 14.1, which I believe is normal.

Then, the measurement from the negative post to the ground strap post was 2.5 mV.

When the ground strap was wiggled, the voltage would go up to 5 mV, but it would take a good wiggle. Most increases would be to 4.5 mV.

Is that out of normal?

j.kenzie@sbcglobal.net

Replace ground strap. It's cheap and the strap gets corroded over time. The fact that the voltage drop varies with position is very suspicious.
Good luck,
Dave

Alan

That it changes is interesting (if real - it may just be the proble location if you were holding it and wiggling it too). These specific readings are not really problematic for the regulator - but I'd still change the ground strap to eliminate it (if the 2x changes were real that indicates an issue).

14.1v is a little high depending on temperatue (higher as the temperature goes down). When at truly warm idle it should be lower than this. If you see the voltage go up to 15V again - testing the battery ground strap then (while its doing it) would be interesting... does it only hit 15V at high RPM? or stay there when its hot?

Did it do all this with both of the last 2 batteries (I think you said you'd done a new battery recently)

It has been known for batteries to have intermittent internal open circuits... (but not two different batteries).

Alan

jwbeck17

Thanks! I was thinking that the fluctuation could be due to probe movement and so I tried to keep it still, but I still saw some fluctuation with some minor ground strap wiggling. That could be the original ground, so sounds like a smart buy.

And I would agree that 14.1 may be slightly high. Yesterday when I measured after a drive it was around 13.8, so I figure that that warm up tonight was not as good as yesterday (which makes sense since I had to leave it idle in the driveway due to weather).

And you are correct, Alan. I only get up to 15V+ at RPMs of 3500 or more. Has to be under load. Otherwise it drops down to normal at idle. The only place I can measure it is in cabin at the radio connection when I am revving the engine.

Still thinking voltage regulator, but I'd like your opinion.

Thank you guys so much for helping me through this!

jwbeck17

Latest update. Grounds are all cleaned, and new ground strap is on its way. I changed the voltage regulator as well. Still same issue on throttle-up. However something new occurred today.

I cleaned the sunroof motor connectors as it was not running consistently, then I took her for a drive. It started to rain, so I closed the windows and turned on the fan. That's when the voltage dropped to ~ 13.4 V. When I increased rpms to above 5, voltage increased but stayed below 14.

And the radio worked fine.

Apart from keeping the fan on 100% of the time, anything those clues tell that I should check?

Alan

Likely the voltage will also stay lower if you leave the AC on also (this puts the cooling fans on) - it's probably just the extra loading that stops the alternator from jumping up to so high a voltage - basically its just masking whatever issue you have that really causes the problem.

Alan

jwbeck17

Just closing out this thread as the problem is solved. The voltage regulator was the culprit. Here is what we found out.

The alternator had a KAE voltage regulator when I had the issue, and I replaced it with another voltage regulator which was wlso KAE. Still had the same issue.

Looking at both regulators, both seem to have that little nick in the end of one of the brushes after use. The rest of the nicked brush was unblemished and never touched the commutator.

Earl suspected that the KAE voltage regulator brushes were not seating correctly due to a possible defect.

I then ordered the internal voltage adjustible regulator from Dave Barton at Dave's Volvo Page. Earl and I then compared the brushes and noticed that the KAE did not line up with the Dave's adjustible one.

Once I installed Dave's unit, there were no spikes at all. Smooth voltage. All we did was adjust the voltage slightly to make sure that the current was a strong 13.9V at idle.

...and the radio works!