914 Alternator Charging issues Options

[kostritzer]

I've been working through a charging issue with my new to me 74 1.8.

This was a car that had been sitting for over 20 years. The guy I purchased it from went through the brakes and the fuel system over the last year to get it drivable, but I don't think he realized there was a charging system issue since the "gen" light was not on when the car was running.

What I found was that although the light would come on when the ignition was on, it would turn off after the car was running. It wasn't until I drove it and saw that the voltmeter in the center console was at 12V did I realize there was a charging issue.

The car came with a new battery that tests well.

Engine running, the light is off and there is only battery voltage at the battery terminals no matter the RPM. Shorting the DF and D+ at the regulator connectors only increased the voltage to about 12.5, so I decided to remove the alternator and get it tested at a local rebuild shop. The rebuilder tested the alternator and said it was good, so I purchased a new alternator harness from 914 rubber and reinstalled the alternator with the new harness and a new belt.

Fired up the car and it's still not charging. Shorted DF and D+ again, and now the voltage increased to about 15V. Assumed that the VR was the culprit, so I looked around online to find a suitable one, and it appeared that the ones available do not fit very well. I did find one thread where someone used a VR650 solid state regulator, so I figured I'd try one of those since I could get one locally pretty quickly.

After installing the solid state VR, the alternator was now charging the Battery at 13.5V, however now the GEN light is only when the engine is revved up. I popped the left gauge out to check voltage at the GEN light and inspect the bulb. There was a 1.2 watt bulb in place. I swapped the oil pressure light bulb with the GEN bulb since it still had a 2 watt bulb. No change. I checked voltage at the red/white F9 feed wire to the bulb while the engine was running, and it's about 13.5-13.8V. Voltage on the blue wire from the alternator/VR was 15-18V depending on RPM!

Now it makes sense why the light is coming on with RPM, but why the high voltage? At this point I'm assuming that the Solid State Voltage Regulator is the problem. Anyone else ever run into this issue?

[Spoke]

When you're doing your measurements, check these 4 voltages:

Battery Voltage: should be 14V
D+: should be equal to the battery voltage
DF: should be 5-9V
D-: should be zero

D+, DF, D- and battery voltage should be measured from a chassis lug.

D+ and battery voltage should be identical as they come from the alternator through different diode pairs. If they are significantly different, there may be a diode issue in the alternator.

Also the voltmeter in the car is not in a good place to get battery voltage. As some have said, it's for vanity purposes only.

[Spoke]

Here's a simplified schematic of the 914 charging system.

[kostritzer]

Here's a simplified schematic of the 914 charging system.

Thanks for the fast reply Spoke. These are my measurements I took back probing the Alternator connector at the relay board engine running:

With the Bosch VR that came with the car

Battery Voltage: 12.3V
D+: 13.5V
DF: 6V at idle, 8V at 2500 RPM
D-: 0

Gen light comes on with key on, does not come on with engine running with this VR

Solid State VR
Battery Voltage: 12.87 at idle 13.9 @ 2500
D+: 15-18V(idle to 2500)
DF: 8 to 4.5V (idle to 2500)
D-: 0

Gen light comes on with key on, is dim at idle and gets brighter with RPM with this VR

I also did a voltage drop test from the starter lug to the battery positive terminal and that was good. Car seems to crank easy. Battery is pretty new.

Side note, do you know where the ground strap from the transmission to the body is supposed to be located?

[NARP74]

Ground strap, top of the trans near the rear of the car, almost straight up to a stud or bolt, bottom side o the trunk floor.

[kostritzer]

Ground strap, top of the trans near the rear of the car, almost straight up to a stud or bolt, bottom side o the trunk floor.

Found it, thanks!

[Spoke]

Thanks for the fast reply Spoke. These are my measurements I took back probing the Alternator connector at the relay board engine running:

With the Bosch VR that came with the car

Battery Voltage: 12.3V
D+: 13.5V
DF: 6V at idle, 8V at 2500 RPM
D-: 0

Gen light comes on with key on, does not come on with engine running with this VR

With Batt being 1.2V lower than D+, it almost seems like a diode is open on the battery side. D+ and VBATT should be very similar.

Solid State VR
Battery Voltage: 12.87 at idle 13.9 @ 2500
D+: 15-18V(idle to 2500)
DF: 8 to 4.5V (idle to 2500)
D-: 0

Gen light comes on with key on, is dim at idle and gets brighter with RPM with this VR

The SS VR results makes me wonder if the VR is oscillating and is not stable. The D+ for the Bosch unit was stable at 13.5V (perfect) but you see variation 15-18V on D+ with the SS VR.

With both VRs it looks like the battery voltage is significantly below the D+ voltage. I won't go as far a saying something is wrong with your alternator but it sure looks like it from the data. Hopefully someone else will chime in with their thoughts.

[kostritzer]

The SS VR results makes me wonder if the VR is oscillating and is not stable. The D+ for the Bosch unit was stable at 13.5V (perfect) but you see variation 15-18V on D+ with the SS VR.

With both VRs it looks like the battery voltage is significantly below the D+ voltage. I won't go as far a saying something is wrong with your alternator but it sure looks like it from the data. Hopefully someone else will chime in with their thoughts.
[/quote]

Quick update. Picked up a Hella Solid State VR from Pelican today https://www.pelicanparts.com/More_Info/0439...3-903-803-b-m44 (they're local to me) and it's behavior is similar to the VR650 solid state regulator except that the voltage is even higher on D+. I was seeing 22V when giving it a quick rev. Also, voltage at the battery is now 13 at idle but going over 15 when revved up. (IMG:style_emoticons/default/confused24.gif)

Thinking it's time to replace the alternator.

[GregAmy]

I chased a similar problem for weeks. My symptoms were GEN light off at low revs, light on at high revs. Did all the basic checks as above and verified there was increasing voltage with increasing RPM.

It was a bad diode in the alternator. Rebuilding the alternator fixed it.

See post 15 below, then read from 23, see if this is your issue:

http://www.914world.com/bbs2/index.php?showtopic=326479

[kostritzer]

I chased a similar problem for weeks. My symptoms were GEN light off at low revs, light on at high revs. Did all the basic checks as above and verified there was increasing voltage with increasing RPM.

It was a bad diode in the alternator. Rebuilding the alternator fixed it.

See post 15 below, then read from 23, see if this is your issue:

http://www.914world.com/bbs2/index.php?showtopic=326479

Yes, that's 100% identical to the symptoms my charging system is showing. Funny thing is I ran across a post you made on the Pelican forum about having this issue exact issue last night and was hoping I could find your post on here to see if you could elaborate! Lol.

Going to pull the alternator again and get it rebuilt locally. No one seems to have a rebuilt unit in stock at the moment unfortunately.

[GregAmy]

Glad I could help.

I'm all about the local rebuilders, the more grumpy and grizzly the rebuilder, the better. Those just seem to work a lot better than the FLAPs overseas "rebuilt" ones.

Let us know how it works out.

[GregAmy]

And coincidentally...I killed my Hella solid state VR yesterday and needed that link to troubleshoot it...lolz

[Superhawk996]

And coincidentally...I killed my Hella solid state VR yesterday and needed that link to troubleshoot it...lolz

@GregAmy

Out of curiosity what did you do to kill it?

[GregAmy]

Out of curiosity what did you do to kill it?

Not sure, honestly. See what you think...it's not a short story...

Car has not been driven a lot this year so the battery was down when I drove it last week. Jumped it, car ran fine, no problems; figured I'd check for a vampire drain later and put it on a battery charger overnight and removed it next morning...

Yesterday, went to drive it and the battery was DEAD. I mean, flat DEAD. ETX16 AGM. OK, so I grabbed my jump pack and as soon as I connected it the fuel pump started running -- key off. Okay...a prob in my Microsquirt design maybe? So I started to drive the car to my destination and when I got 4-5 miles away from home and it started to die on the highway...felt like the fuel pressure was decaying. Pulled over and clearly the battery was flat. Rejumped it - I brought the jump pack* with me - tried to baby it home, and it died again.

Got lucky in that the third time it died right at the curbside of a new AutoZone - I coasted into their parking lot - and they had the ETX16 AGM battery so I just bought a new one to get me home.

Broke out the multimeter at the house, yup no chargie. Also noticed it had no GEN light with key on (don't recall if that was a prob prior).

Did the basic alternator test (DF to D+) and verified the alty was putting out so I grabbed another Echlin VR I had sitting around and it charged fine.

And that fuel pump problem? That was me being stoopit. I have - had - an old fuel pump relay with the top plastic cut off; I used it as a tool to test the fuel pump and pressure by pushing down on the reed at the top to make the fuel pump stay on. Well, I neglected to replace it with a sealed relay and apparently some water got into it and corroded the terminals together...making the fuel pump run constantly with the key off. It wasn't running the last time I left the car in the garage so I never heard it...and it's a damned good thing that I don't have a fuel leak anywhere.

So, TL;DR, fuel pump relay failing on, causing the battery to go totally flat, so maybe by my jumping a totally dead battery and making the alternator work hard I killed the Hella VR...?

Cars, yay. - GA

*Top tip: the "IMAZING" Jump Starter 2000A lithium pack is a pretty cool toy - it'll jump a Ford F350 gasser - but it has a flaw: it turns off after about 30 seconds. So I could not use it as a supplementary battery to get home.

Good jump box, bad battery supplement.

[Superhawk996]

, so maybe by my jumping a totally dead battery and making the alternator work hard I killed the Hella VR...?

Yeah that’s a tough one to root cause. I think you’re probably right. Dead battery forcing lots of field current through the regulating transistor at a 100% duty cycle probably roasted it.

Don’t get me wrong I like and prefer the Hella solid state VR but it’s times like this (high current flow, high heat) that a good old mechanical regulator may have held up better with mechanical contacts.

Thanks for the story - may be a good reminder to not try to charge a completely flat battery in car.

Recently my Wrangler is going dead flat due to an aging battery, non-use (don’t drive as much in summer), and usual (expected) parasitic draw. I’ve been tempted to just jump start it and let the alternator try to change it but both times have thought better of it and put on the battery charger 1st. Thanks for the reminder to keep doing this!!

@GregAmy

[kostritzer]

Glad I could help.

I'm all about the local rebuilders, the more grumpy and grizzly the rebuilder, the better. Those just seem to work a lot better than the FLAPs overseas "rebuilt" ones.

Let us know how it works out.

Update on the charging issue.

Took my alternator to a local "old school" rebuilder to get sorted. They threw it on their bench tester after I explained the symptoms, and right away the guy said "Yeah, it's humming, sounds like diodes". Dropped it off in the morning, and picked it up that afternoon. Total bill $125 including a 12 month warranty.

Got it back in the car tonight and all is well. No light, and it's charging at a solid 13.8V with the Hella VR, and 14V with the VR650 from Autozone.

Thanks for your help! Now to sort the vacuum leaks and shift bushings!

[Spoke]

Awesome.

(IMG:style_emoticons/default/beerchug.gif)

[GregAmy]

(IMG:style_emoticons/default/piratenanner.gif) (IMG:style_emoticons/default/beerchug.gif)


We're going to soon lament not having those guys around...