Charging question on a 914-6 Options

[db9146]

Well, I have made a temporary conversion of my -6, inserting a rebuilt 2.7S with ITBs, MS3, and distributorless ignition in place of the tired 2.0L. Before putting the engine in, I decided it best to install a new alternator along with a new engine/alternator wiring harness.

The alternator is for a 1965-1977 911 2.0-2.7 that uses an external VR.


and here's the new wiring including a new ground strap to the engine case.


The large red cable goes to the starter, the smaller red wire is D+, the black is DF, and brown is D-.

I thought the problem might be the battery because of its age but when I checked the output of the charging system at the battery, there was none. I replaced some of the dash lights with LEDs but made sure not to replace the GEN warning light, which is not coming on despite the alternator not charging.

Should I next pull the D+, DF, and D- plug and check for alternator output across DF and D+ momentarily?

If there is output, what then?

If not, what's next?

[larryM]

see my updated notes with pics below

http://www.914world.com/bbs2/index.php?showtopic=327218

http://www.pelicanparts.com/techarticles/1...Replacement.htm

http://nodasystech.com/design/porsche-911-...ing-diagram.php

http://www.aa1car.com/electrical.htm

http://easyautodiagnostics.com/misc-index/...ad-alternator-1

[db9146]

Thanks Larry.

I hate electrical issues.....


Okay, the GEN light was on with the key on, and off as soon as I started the car yet when I checked the battery charging, the battery voltage was unchanged with the engine running at a fast idle.

So I swapped the VR and tried again. I am now seeing a voltage increase to 13.14.... better but still not what you would expect. I'm measuring with a multimeter across the terminals with the engine at about 1800-2000.

The harness from the new alternator to the starter motor and from the starter to the battery is all new and built from one of Perry Kiehl's kits, so its all properly sized. I installed new braided grounds at the alternator, the trans, and the battery. I've checked the battery and trans and they're tight. I remember distinctly tightening the strap on the alternator to engine case (and oriented it so it would foul anything). I did paint the trans but I can't believe that would be an issue with a new braided cable and hardware.

Any other ideas to consider to improve the low charging voltage?

[SirAndy]

How exactly are you testing the output?

I know at least on my /6, i have to blip the throttle to get the engine over 2k+ rpm after i start it for the alternator to kick in and produce current.
If i just let it idle, it won't charge and the warning light stays on.

I've been told that this is somewhat normal ...
(IMG:style_emoticons/default/idea.gif)

[db9146]

Last night, I measured the voltage at the battery again with it fully charged before I started. It was 12.8V. I turned the key (GEN light came on), then started it up (rev'ed it and GEN light went off) and measured the voltage at the battery again - no change.

I then replaced the VR with a "new" old VR that I just recently bought and measured the voltage again. This time it was about 13.15 at an elevated idle. So now it seems like its charging but not much, so I checked the chassis strap to the trans.

I removed the nuts and strap, checked that the area was as clean as I thought, and reattached the new strap in between.

I then moved to the ground strap connection for the battery. Before I installed the new engine, I repaired the ground stud which the PO had twisted off, cleaned up the area, and installed the new battery ground strap. Everything looked good and was tight here.


Even with this, I checked the battery voltage again and got 13.10, slightly less than I had measured before removing, checking, and reinstalling the trans ground strap.

[Mark Henry]

Last night, I measured the voltage at the battery again with it fully charged before I started. It was 12.8V. I turned the key (GEN light came on), then started it up (rev'ed it and GEN light went off) and measured the voltage at the battery again - no change.

I then replaced the VR with a "new" old VR that I just recently bought and measured the voltage again. This time it was about 13.15 at an elevated idle. So now it seems like its charging but not much, so I checked the chassis strap to the trans.

Like Andy said you may have to take a speed run well over 3000rpm. The 13.15 is likely good, a points style regulator the voltage will fluctuate at least half a volt.

Do you have a gel cell battery? They always seem low compared to a wet cell.
The 12.8v fully charged could be perfectly normal if it's a gel cell like an optima.

[Spoke]

If GEN light is on when key is ON and engine not started, then goes off, it sounds like the alternator is working.

[db9146]

MH and Spoke, I had started my last post earlier this afternoon and got interrupted by work....go figure.

Anyway, I did install a new Bosch AGM battery so these measurements are with it. The VR is an NOS Bosch metal can unit but I'm seriously contemplating a new SS one or even one of the variable VRs but I want to determine that everything is really okay before I go to an adjustable VR and cover up the symptom (lower charging voltage).

[db9146]

This is getting screwier by the moment......at least in my mind.

Tonight, before I started the engine, I measured battery voltage (new Bosch AGM, Group 48)...it was 13.11. Then I started the engine and idled it up, turned on the headlights and measured again....12.89. Turned the lights off, measured again...12.88. Hmmmmm.

I was about to pull the VR and jumper between DF and D+ when I jumped over and read this doc. (http://www.ratwell.com/technical/ChargingSystem.html#vrtest) on charging system testing. In it, it specifically states not to run this test as it can damage sensitive electronics such as ECUs!!! I''m running MS3x so I'm glad I read that...whew. But I did figure out a way to get a measurement at D+ below.

In the same doc, it gave measurements for ohms across, D+, D-, and DF terminals of the VR:




Next, I checked the alternator harness since I had built it new when I installed the new alternator in the engine last year. It checked out fine as well. Then, with the engine running, I pulled the alternator 3-pin connector loose from the circuit board just enough that I could get a multimeter probe under the connector housing and touch the spades for a direct measurement.

On the D+ pin at idle, I measured 13.7V. On the DF connector at idle (750 RPM), I measured a stable 7.4V, But when I idled up the engine to about 1800-2000, I measured the same 13.7V on the D+ pin and an erratic 3.7 - 4.? on the DF pin.

I believe the D+ pin should be reading the full output of the alternator before the voltage regulator, should it not? If so, then why was I only getting 13.7V? Shouldn't the reading have been closer to 15-16V?

[db9146]

You can also measure the unregulated output of the alternator by measuring between the lug on the starter where the B+ cable connects and a ground point, correct?

[Mark Henry]

Is this alternator out of a 911 with the dual batteries?

IIRC the alternator for this has a lower output voltage, something to do with the dual batteries not being able to handle higher charging volts. So this could be normal for this alternator.

I don't have time to search this, but I'd check it out.

[Spoke]

On the D+ pin at idle, I measured 13.7V. On the DF connector at idle (750 RPM), I measured a stable 7.4V, But when I idled up the engine to about 1800-2000, I measured the same 13.7V on the D+ pin and an erratic 3.7 - 4.? on the DF pin.

I believe the D+ pin should be reading the full output of the alternator before the voltage regulator, should it not? If so, then why was I only getting 13.7V? Shouldn't the reading have been closer to 15-16V?

In the above measurements, I assume the VR was still operating in the system.

The D+ pin is the output of the alternator to the VR. The VR will vary the voltage on pin DF based on the voltage it sees at D+. The VR will try to keep D+ in and around 13.5V or so, exactly what you are measuring. It will regulate D+ using DF to vary the magnetic field in the armature (rotating part of the alternator).

As far as the erratic voltage at D+ when the engine RPM are up, this could just be the normal regulation of the VR. As the engine RPMs increase, so does the output of the alternator increase. The VR will likely lower DF to maintain 13.5V or so at D+. If a voltage is moving around quickly, a DVM is not so useful and an oscilloscope is needed to be able to "watch" the voltage fluctuate.

D+ will only be 15-16V when D+ is shorted to DF as the alternator will be producing maximum voltage.

[db9146]

MH, the engine is from a ‘74 911S but I’m not aware if they had dual batteries.

Spoke, thanks for the explanation. I understand what you have explained but I guess my only remaining question is: if the alternator was generating 13.7V, then why wasn’t I measuring 13.7V at the battery? I have always thought that measuring voltage across the terminals of the battery with the engine running was a measurement of the regulated output of the alternator. That’s why I was thinking that I had a charging problem. (BTW, I’ve got a full set of your front and rear LED lights. I love ‘em.)

I have a new SS, adjustable VR on the way and will see if that makes a difference in the charging measured at the battery.

[914Sixer]

74 911 was a single battery.

[db9146]

Does anyone know the wattage of the light bulb in the combo gauge that tickles the alternator to start working? I need to confirm I have the right one....still chasing an issue and Okteenerfest is fast approaching.

Is there a specific wattage or just any incandescent 12V bulb?

[larryM]

you wrote above: "the GEN warning light, ... is not coming ON"

if it is never ON, then you are not getting 12v field exciter current to the regulator

- your initial problem is to get juice to & thru that bulb & to the VR so that the VR can energize the alt field

"2-3 watt bulb is enough for normal alternator excitation." Scroll to page 20 of this > https://woodmizer.com/us/portals/0/docs/743...9c0c8e77ef1.pdf

iGN ON (not running) - measure the voltage on the (blue) wire which should be attached to that bulb - where it connects to your relay panel - so you know if you have current twixt the ign sw & thru the bulb to the next potential roadblock item (the panel) - if ya got 12v there,

if you ground that wire the bulb should light, which tells ya circuit is active to that point

then see if you have 12v at the VR plug (color of wire is different after it leaves the panel) - if ya got 12v all the way to the VR, (and you already tried a new VR) then your alt field is not energizing, thus no output

you should read 12V at field wire DF - if you then jumper DF to D+ with a fused jumper, (engine running) you should get full alternator output - if no 12V at VR DF with ign on, then your problem is upstream, either a bad regulator or bad wiring to dash & ign

OR - possible bad alt or incorrectly wired at the back of alt

here are pics of some notes from back in 2009-10 when i had a similar problem (difference: my -6gt- never had a relay panel)

[porschetub]

Thanks Larry.

I hate electrical issues.....


Okay, the GEN light was on with the key on, and off as soon as I started the car yet when I checked the battery charging, the battery voltage was unchanged with the engine running at a fast idle.

So I swapped the VR and tried again. I am now seeing a voltage increase to 13.14.... better but still not what you would expect. I'm measuring with a multimeter across the terminals with the engine at about 1800-2000.

The harness from the new alternator to the starter motor and from the starter to the battery is all new and built from one of Perry Kiehl's kits, so its all properly sized. I installed new braided grounds at the alternator, the trans, and the battery. I've checked the battery and trans and they're tight. I remember distinctly tightening the strap on the alternator to engine case (and oriented it so it would foul anything). I did paint the trans but I can't believe that would be an issue with a new braided cable and hardware.

Any other ideas to consider to improve the low charging voltage?

Interesting reading as I have the same issue almost exactly,same new parts even,rebuilt altenator,new loom,new NLA regulator,repaired relay board and new ground leads, I haven't done the relay jumper as yet as spoke mentioned and that will be my final attempt before pulling the altenator,I have a small GSM battery and someone mentioned funny things can happen with these...I just don't know.

[Spoke]

So I swapped the VR and tried again. I am now seeing a voltage increase to 13.14.... better but still not what you would expect. I'm measuring with a multimeter across the terminals with the engine at about 1800-2000.

I recently checked my 930 battery voltage it wasn't much different from your 13.14V. I was surprised it was that low but I haven't had trouble with the charging system.

If the battery voltage is over 12.6V when running then the battery is being charged. If you have trouble starting the car then maybe more attention to the charging system is needed.

[db9146]

LarryM,
Thanks for the great additional info!!! Saved it for reference.

Tonight I checked and:
- I have a 12V 2W Osram buld in the GEN socket
- it lights when I turn the ignition on
- it goes out a moment or two after the engine starts up
- I get 12.5V at the dash light
- 12.5V at the D+ female on the circuit board that the VR plugs into
- 12.5V at the D+ male spade on the circuit board that the plug from the Alt. connects to
- and 12.5 at the DF male spade on the circuit board that the plug from the Alt. connects to.

LarryM, you mentioned that the issue may be upstream in the wiring at the dash or ignition switch. If I'm getting 12V at the GEN bulb and D+ on the circuit board, wouldn't that indicate that the wiring between the circuit board, dash, and ignition switch is okay?

I understand that the next step is to try to measure the full alternator output by jumping DF to D+ but I really don't want to do this because the new engine is running individual throttle-bodies and MS3x. (CAUTION: Voltage is unregulated during this test and could damage sensitive electronics. {Balmar Alternator - Regulator Troubleshooting}). I think that means that I could kill my ECU.

It seems I really need to find another way to test the alternator.

NOTE: Before trying to perform the full field testing, I read that one common way to test modern alternators is to test for a magnetic field with a screwdriver once the switch is turned to the "on" position. However, I don't this will work on a Porsche -6 since it relies on the bulb to provide the resistance to "tickle" the alternator into charging.


(Man I don't want to drop the engine for this....)

[db9146]

If the battery voltage is over 12.6V when running then the battery is being charged.

Spoke, why would you say that the battery is being charged at only 12.6V measured voltage at the battery with the engine running? I have always seen a figure between 13.6 and 14.4 as the output for a properly operating alternator. And yet, a couple weeks ago I took the car out for a drive in the evening and had the lights on. I stopped and had to get a jump to get the car started again. In talking with a friend this morning, he commented that if the old battery was so dead that it wouldn't start the car and then it ran fine the entire way home after a quick jump, that the alternator must be putting out some power just to run the engine and lights on the way home....a simple jump would not have provided the juice necessary for that.

So honestly, I am coming back to your comment and wondering if the new battery I installed and checking of all of the grounds didn't fix the problem....and I'll just have to adjust to a new "normal" charging voltage. I really can't think of another way to test the alternator output if I can't perform the full field test for damaging the ECU.