Remanufactured Alternator Readings - Need Input!
 

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?

http://forums.pelicanparts.com/uploa...1256913570.jpg

http://forums.pelicanparts.com/uploa...1256913581.jpg

http://forums.pelicanparts.com/uploa...1256913590.jpg

http://forums.pelicanparts.com/uploa...1256913596.jpg

http://forums.pelicanparts.com/uploa...1256913602.jpg

http://forums.pelicanparts.com/uploa...1256913616.jpg

http://forums.pelicanparts.com/uploa...1256913628.jpg

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

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.

How about Alan? You out there?

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?

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

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.

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

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.

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

Neil,

What is Dash VM? And where is it located?

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

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

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 ;)

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

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!

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?

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.

3/4" movement is WAY too much.

Alan

Maybe I am on crack. I will shoot a quick vid of the flex. I'm afraid to go tighter and start damaging bearings.

Spoke to the seller and he has a 120 amp that I can trade out with (pay difference). I'm gonna go with this. Will post more readings when i get the 120 amp installed.

Hello all! Sorry I haven't posted more on this topic when i put in my 120 Amp alternator in. I still get light dimming and I can see my volt drop to under 10 in my stock Volt Gauge upon low rpm's. I did all the 14 pin and Post cleanup and still the same. I am really kicking myself for not just doing the Delco Swap in the first place.

When I was cleaning the 14 Pin, I did notice the wire that goes to the Alternator (exciter?) and it had a little greenish tinge to it. Would it make a difference if I just ran another wire straight from the 14 Pin to my Alternator?

No - your alternator is starting up OK. I think you just have belt slip at idle.

Alternator belts need to be super tight. Take it to a shop - they will know how tight to crank it.

Alan

Thanks Alan for the reply. I will try and tighten it up again. Is there some sort of way to gauge the proper tightness?

Leo,

According to the shop manual, the belts should (flex) give 10mm at center between pulleys.

Hi MPDANO...i went through 2 reman 90 amp bosches , and one 140 amp new bosch, always weak! i ended up putting on a 200 amp delco 1 wire alt. never a problem again. idles at 14+amps and drives at 13+ even w/ lights and stereo on. best ALT ive ever bought..cheap too!

BTW if it has been slipping for a while the belt will be in poor shape - the inside surface will get glazed from the friction and will slip more than a new belt would.. You may be able to feel this... It will be getting hot at idle also.

Alan

Thanks Jim and Alan. I will first check the belt and get it to specs. Also, will check the belt condition. If all those fail, it's Delco swap time. Much appreciated for the info.

I have the EXACT same symptoms in my 82, along with an intermittent tach and bouncy oil pressure needle.

I'm wondering if my light dimmer switch under the dash on the left has high resistance in it? I'll bet it does. Dimmer switches never last. Maybe I'll over-ride it because the lighting is so weak anyway.

The easiest way to fix all that jumpy stuff is to replace the PCB (Printed Circuit Board) on the back of your Instrument Panel. Also, just jump that dimmer with 2 spades and a wire. If I have daylight when I get home and it's not raining, I will tighten the Alt Belt and see if that helps. I will report back either way.

Have you already over-ridden your dimmer switch?

Is it a huge pain in the butt to remove the pod?

Not hard to remove your Pod, especially when you remove it as much as I do. My 81, it's all the plates underneath the steering wheel and behind it. Those are held by Phillips Screws. Steering Wheel and Signal Stalk comes off. Then 2 10mm long bolts hold the Pod. When you start lifting it out, be very careful of the 2 main plugs as where they plug into is very brittle plastic. I am sure if you search on my username and pod, I have mega pics of me doing it.

Yes, I don't use my dimmer. The wires are plugged together.

Here's a link to a lot of pics when I changed out my PCB and put some reflective foil to reflect the lights better.

http://porsche928forums.com/viewtopic.php?f=9&t=4&st=0&sk=t&sd=a&start=520

Awesome. Thanks. :)

Great Pics

FYI, tightened my belt last night and same issue this morning. Looks like Delco Swap out. I plan to do some stuff that will require more electrical power so I can't have this. More to come.

I want one of those high output alts, too. Where from?

eBay is where I got mine. Obviously not working very well. Why would you follow my grief. My suggestion is don't do it, unless you want to buy mine ;) I'm going to Delco Swap it.

Delco is the company that builds electronics for General Motors. You can go to any auto parts store (with your Bosh Alt.) and tell them you want a chev alt with the same mounting placement in 100 amps or more. they will more then likely sell you a standard 110 amp alt.
I was going to rebuild my bosh but now that i see this thread I will do the swap to the chev Alt.
I have done this to many fords and implement equipment before. They are a good replacement.