Remanufatured Alternator Readings - Need Input!

[MPDano]

Hey guys,

I finally got around to replacing my tired Alternator (was on car when bought and have no history).

I ended up buying a Stock 90 Amp Remanufactured Alternator and took readings before and after.

I also drove the car in to work today and still have that "in gear" dimming of Instrument Lights until RPM's brought back up. This can't be right. It's a pretty new Battery from earlier this year from Autozone.

Old Alternator:

Car Off: 12.59 Volts
Fast Idle (warm up): 14.20 Volts

New Alternator:

Fast Idle (Warm up): 13.64 Volts
Low Idle (Car warmed up): 13.30 Volts
Low Idle, Lights on: 12.81 Volts
Low Idle, A/C on, Stereo on: 12.67 Volts

Do readings seem correct? Or do they seem low? Thoughts?

[MPDano]

[Mrmerlin]

those numbers sound about right , remember that the charging system weakness in the Porsche is at idle.
once the idle gets to about 1500 you should be seeing 13.8 to 14.2
If the charge never goes over 13.4 then you probably have a bad diode

[MPDano]

Thanks for the quick reply MrMerlin. So does the dimming of Instrument Lights on 928's normal? I know there is an alternate Alternator swap (Delco), but this is straight Stock for Stock. Same Amps.

[MPDano]

How about Alan? You out there?

[JhwShark]

Well I'm not Alan, but:
I have seen many posts as well as replies to my own that indicate if voltage is good at key measurement points that connections and/or ground contacts could be dirty downstream. Have you checked the voltage at the instrument cluster compared to the jump post? You do not say where you are taking the readings. From experience the bad diode is one possibility though.

Just trying,
Jon

[MPDano]

Originally Posted by JhwShark

Well I'm not Alan, but:
I have seen many posts as well as replies to my own that indicate if voltage is good at key measurement points that connections and/or ground contacts could be dirty downstream. Have you checked the voltage at the instrument cluster compared to the jump post? You do not say where you are taking the readings. From experience the bad diode is one possibility though.

Just trying,
Jon

This is possible since I don't see my other lights dimming at all. Center Console, etc are fine. It seems to just affect the Instrument Panel. Also, voltage at Stock Gauge is always low. Not sure if this it connected? What terminals would I check around the Instrument Panel?

[JhwShark]

My voltage on stock gage is low as well. I get good readings to CE panel, have cleaned my grounds (they were not bad) have cleaned jump post connections and noticed that the Red leads which go to the CE panel are slightly degraded but at CE panel connection points for them they read same as jump post. That leaves between CE and instrument cluster. I do not have any dimming at idle; so...

The recommendation was for me to clean the blue foil (the metal stripes on it) with the white eraser; also clean the connector to the cluster. I have not gotten back in there yet ( I had it out to repair the odo gear a few months ago) to clean up the strip. I understand that possibly newer models have a potentiometer that can be used to calibrate volt gage, I did not have on mine.

Also, on some Ins clusters the silvered plastic reflectors for the dash illumination bulbs fades over time which could accentuate the dimming you experience. The can be carefully removed and resilvered (or use refelctive foil). Mine are fairly OK, and I have not wanted to try this reflection fix yet; I get enough reflection to see what I need, though it is not great.

Jon

[MPDano]

Yeah, I am starting to feel I will need to yank the Pod out again, but no biggie since I was gonna do that anyways when I start servicing the Diaphragms on my Actuators (HVAC).

I did all my readings from the battery posts in the rear of the car. Do you think you can post some readings from yours? If it's not too much trouble. I would like to have a comparison of sorts.

[JhwShark]

Sure,
12.8v off, 13.8v while ON at Bat
12.8v off, 13.8v ON at Jump post
12.8v off 13.8v On at CE three Red leads connectors
12.8v off, 13.8v ON at pin #30 of fuel pump relay and start relay (or at it's Pin location if manual trans)
I have not done a reading on pin 15 while ON since I fixed things but it will read lower (it read about 1v lower before I replaced my Bat).

adding...the ON is at idle 850rpm, I did not take the revs up to check uper range output

[neil30076]

Leo, FWIW, I'm still running the original Marchal alternator that came on my car, replaced the regulator module once in 28 years, and my voltage readings are :

Jump post under hood:
Engine off: 12.6
Idle : 13.7
2k rpm : 14.1


Cig lighter:
Idle: 13.3
2k rpm : 13.9

Battery:
Idle: 13.1
2K rpm : 13.7

Dash VM :
Key in position 1 : 11V
Idle : 12.2
2k rpm : 13.

[MPDano]

Thanks guys, I am copying them next your posts to compare easier.

Old Alternator:

Car Off: 12.59 Volts
Fast Idle (warm up): 14.20 Volts

New Alternator:

Fast Idle (Warm up): 13.64 Volts
Low Idle (Car warmed up): 13.30 Volts
Low Idle, Lights on: 12.81 Volts
Low Idle, A/C on, Stereo on: 12.67 Volts

[MPDano]

Neil,

What is Dash VM? And where is it located?

[neil30076]

Thats my British way of saying the voltmeter/ stock gauge in the pod :-)

[neil30076]

Thats my British way of saying the voltmeter/stock gauge in the pod :-)

[MPDano]

Now I am 90% positive that it's in my Panel itself as Jon mentions. My old alternator was most likely fine. All good, at least I know the history on mine now. And my readings are very similar to both of you.

Also, Neils Instruments also dim at low idle. Oh well, who really stops at lights here anyways. California Roll

[Alan in AZ]

Well the numbers are a little low at warm idle for a new alternator but the alternator is still just barely keeping up with demand (based on the absolute voltage levels) so it is working.

You shoudl do measurements at the front jump post to determine the alternator output more directly.

Its also possible you have a belt that is not tight enough... alternator belts slip at idle not usually at any other time - because the relative loading is much higher at idle.

A way to tell is to see if the belt gets unduly hot while just idling under load (warm engine) vs when not loaded.

Generally cleaning the pod connectors is a good idea, cleaning the front jump post connectors is also easy and well worthwhile. clean gently until bright and use a chemical terminal cleaner (stabilant/deoxit) and after reassembly use a contact protector (spray) to reduce future deterioration

Alan

[MPDano]

I'll re-check my belt again but i made sure I only had flex the same thickness of the belt. 3/4 inch flex?

Also, I will run the numbers again but at the front post.

Thanks for the reply Alan!

[Danglerb]

Neil, seems like more of a difference between the jump post and battery than I would like to see, but was this right after starting when the alternator may have been charging at a higher rate?

[MPDano]

I got 13.55 Volts at the Front Post at Warm Idle.

It got a little too late for me to do a 2K rpm test.