73 Bay Window T4 1.7L - Question on Alternator Voltage

[MikeyM73]

Hi all, happy holidays. Along the journey of bus fixing up (not restoration... yet) I ran across a voltage issue that I was hoping to get input on.

Short story - rescued from a field, sat for 10 years, fixed/replaced damn near everything safety / steering related. The charging system seemed ok but have yet to fully inspect.

The issue is when during the day, running at idle, lights off, I get high 13s to low 14s voltage (regulator is 6 mos old as I was getting 16+V before replacement - cost about 35 bucks). When I turn the lights on the voltage drops to as low as 11.1 at idle and gets as high as low 13s. Here's the deal - the engine is tuned very well for what it is and the shape it's in and runs seemingly perfectly during the day but when the lights come on and voltage drops, after a few seconds, the engine starts to sound like a cylinder is cutting out (Pertronix FFIII dizzy). Turn off the lights, after a few seconds, running fine again. I'm not sure if this is some odd coincidence although, I have swapped plug wires, dizzy cap, and same result.

I've tested this a few times and only when the RPMs are low, this happens. On all other cars I've dealt with, I've always seen 13.5+V as the bare minimum at idle.. usally 14+V at idle, well after warm up. What voltage do you all see with lights on, idling?

Anyway, the point of my blabbering is to ask if the possibility of not having enough voltage could exhibit that kind of issue. I have the Bently and have tested charging systems before, just not old school VW systems. Any advice / input would be very much appreciated.

Thanks much and cheers,
Mikey
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'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[SGKent]

it really depends where you are measuring the voltage. If it is measured at the battery it would be a weak battery. If it is at the front of the car then that means you are losing 2 volts +/- between the back and front in resistance. I'd start checking across each connection and clean up any that are really bad. On my 1977 I had something similar. Found 1/2 volt here. .2V here etc until now the front wiring reads about 13.5V when the back is 14.0V. The headlights are slightly less but I don't want to add a relay to solve it. You will find some voltage drop across the fuses, and the switches. If it is across a fuse you can spin it and that might clean up a little. Also there can be loss in the grounds so don't assume that the grounds are perfect - clean them. You may have to replace some connectors and grounds fasteners. I had to clean and solder a few to get back some of the loss.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[MikeyM73]

Thanks, SG.. makes sense. I'm seeing that voltage reading up front, to a little 'plug into 12v socket' digital VM. I'll start by checking the voltage at the battery while the lights are on and see what the difference is.

When you experienced your issue, did it cause similar running issues?

Thanks again,
Mikey.
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[MikeyM73]

Update - Voltage right off the battery, engine off is 12.2-12.4ish, at idle w/ lights off is 12.2V, lights on is 11.9 maybe 12. These readings right at the batt.

up front from my plug in volt meter, I'm seeing a full 1V drop w/lights on... about 11.2-11.3V and within a few seconds of pulling the lights on, I start to hear the engine just barley go lower in RPMs then a few more seconds it, again, sounds like a cylinder cuts out. I barely touch the gas just to bring up the idle and all is fine, again.

Measured at the coil, engine running, lights off = 12.2ish, lights on = 11.1-11.3ish.. same as the reading at the dash meter. Could this be marginal voltage for the ignition system?

So I would expect to see at least around 13-13.5 at idle right off the battery, right after I fire the engine, no?

I should also mention that after driving for a bit, lights on, voltage up front reads around12-12.5 max. Once I stop at a light or stop sign, voltage drops to around 11.5-11.7ish.

Thanks,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[Wildthings]

You might have a bad diode or bad connections in the alternator. The regulator can not compensate for an alternator that is not working up to par.

[mikedjames]

I would guess the alternator is basically OK because it gave 16V with a faulty regulator.

I would expect 14 volts or more at the battery when charging properly.

Check the warning light on the dash comes on with the ignition on and the engine stopped.


Then I would try another regulator.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[telford dorr]

The output of an alternator is a function of the rotor current and the engine speed. The rotor current is controlled by the regulator and can be monitored by measuring the voltage at the Df terminal relative to ground (type 4 alternator). Once the Df voltage reaches battery voltage, the alternator will be producing maximum output for that engine speed. [Note: type 1 alternator Df voltage is measured relative to D+, as they're wired differently inside. Unfortunately, unless you have the early three-terminal externally regulated Motorola alternator, you can't access the Df terminal to make this measurement.]

It is not unusual for alternator output to fall below that needed to run the lights at night at idle. The alternator in a bus has to handle a much higher RPM range than that in, say, a Chevy Suburban. A bus typically runs continually at 3000 to 4000 RPM while being driven on the highway, but idles at around 900 RPM. That's a 4X speed change that the alternator / regulator has to handle - not an easy task.

This is usually not a problem, as the battery can cover for the alternator, as long as you spend way more time driving than idling. The problem comes from the fact that electronic ignitions can be voltage-sensitive - more so with the inexpensive types. For units which must fit completely within the distributor, there's not a lot of room for the extra components which would be needed to compensate for this problem. Note that the VW unit used in the 79 and later buses used an external controller for this reason. The only solution is to (1) try a different brand of electronic ignition, (2) switch back to points, which don't have this problem, (3) increase the idle speed to try to increase the alternator output, or (4) find the points of voltage drop between the battery and the front of the bus and fix them.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[MikeyM73]

Thanks all. Telford, I do have the external regulator (newer solid state unit which, I believe, is plastic along with the mounting bracket) so i would simply check running voltage at that DF terminal?

I would like to also add that my battery light does not light up with the key on but engine off.. in fact, during our Christmas parade a couple nights ago, the battery voltage (measured at the plug in meter up front) showed the voltage got down to 9.3V and the light never came on.. now, we did have a small inverter clipped directly to the battery so maybe it was simply too much load. But I guess my point is that my battery charge indicator light does not come on but I still seem to be charging.

PS - I'll check the bulb in the light when I get home, tonight.

Thanks,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[telford dorr]

OK, that's the first thing to fix! No light, no operation (unless someone cobbed up something, in which case it needs to un-cobbed and restored to stock). Voltage readings are relatively meaningless in the mean time...

But once the light works properly, then measuring the voltage at the Df terminal will tell you what's what.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[MikeyM73]

So that is very confusing, then. The rear of the instrument cluster looks to be unmolested. And my plug-in battery charger shows to be at high 13’s to low 14’s in voltage when the RPMs are high. How could that be? PO hack somewhere?
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[MikeyM73]

So… I found the issue… Or most of it, I believe. Yes… I can except the fact that I am a dumbass at times… The bulb was burned out. Now, when I turn the key on the light lights up. As it should. I am now charging at 13.5+V immediately. Lights on, I go to 12.7... much better. However the light dims more and more as the engine continues to run. Is this a normal thing Since the battery is charging? And once it reaches close to full charge, voltage on both sides of the light stabilizes and it goes out completely?

I would like to thank all of you very much for your patience and willingness to help. Every week or so one small thing, that cumulatively adds up to a big thing, gets discovered, repaired, made better… Pretty much because of y’all, here. So thanks again.
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[Wildthings]

I would not expect the voltage to drop over time, but after start to quickly up climb to say 13.5 volts and then slowly creep up to say 13.7 as the battery becomes charged.

[telford dorr]

NOPE! Still not right.

The dash indicator should go out IMMEDIATELY after engine start (or maybe after reving it up once). No? Then keep checking.

p.s. wouldn't trust the meter on a battery charger, as you don't know how it's wired inside. Use a real meter. If nothing else, get a free one at Harbor Freight...
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[MikeyM73]

DOH!! Well, heck! That makes sense. So what could/would cause the light to dim and brighten as the RPMs decrease/increase? Now, granted - the undercarriage of this thing is still full of cobwebs, dust, etc. but all on the alternator looks to be wired correctly.. it is night time here and I can't see well so I will check more tomorrow. BUT... at least it idles, when cold, and doesn't sound like it's going to die or run on 3 cylinders.

PS - The voltage meter is one that I plug into my wired in 12V plug.

For what it's worth - not sure if relevant - whatever the wiring harness is that has 2 wires and (I think) went to the coil, the small one is cut with a replacement wire going to the ignition switch while the large one is still intact.

You guys rock. Thank you.
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[MikeyM73]

Slight update - although charging starts pretty much immediately and the charge indicator light now comes on with the key, I'm still getting a 1V drop, maybe a tad more when the lights are on. 13.6-13.8 idling, lights off, drops to 12.4-.12.6 w/ lights on and if I let it idle, that voltage goes lower. And the charge light is on dim. And it doesn't seem to go much above 12.5/6ish while I'm cruising at 3k RPM + (lights on).

Tomorrow, time permitting, I plan on cleaning all the connections I can find to see if that makes any difference.

Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[SGKent]

give the battery time to charge. It might be pulling extra current because it is a little discharged.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

The power to the front has to go through a long piece of wire that is none to big and thus you get more voltage drop than many cars and trucks see. Feeling for hot connections at the starter solenoid B+ post and at the fuse box can help. Cleaning the connections to shiny metal and dosing them with dielectric grease can help.

If your battery has gotten run down, it can take hours to bring it back up to a full charge, until then there will be additional voltage drop between the alternator and the battery which will of course effect the voltage up front as well.

You should check the voltage at the alternator when you lights begin to dim, this will tell you if the alternator is doing its job correctly or not.

[MikeyM73]

Thanks again. I'll put the battery on a trickle charge overnight then see what the results are.

SG - I know this is subjective, but any idea on how long you're referring to? At this point, the only thing I'm sure of is my indicator light was burnt out so I'm starting from there. BUT, it had never worked since we got the bus back in 2016.

Wildthings - my apologies, I meant the battery charge light dims after the engine runs for a bit, not the headlights.

Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.

[telford dorr]

First, familiarize yourself with this (the wiring we're interested in is highlighted). Print it if you can:

Note the blue wire in column 3 that goes from the regulator to the indicator K2 in column 42. This is your ALT light on the dash. Now note the black wire from the same indicator going through fuse S11, then back to the ignition switch "D" in column 16, and then via a red wire to the fuse block, then via a red/white wire to the starter in column 7, then via a red wire to the alternator in column 3. The indicator is lit from a voltage difference between these two sets of wires.

Now generally there isn't any voltage drop along the blue wire, as it only goes a couple of places. The problem is inevitably somewhere along the red and black wires. Look at all of the connections along this path! If any one of them is flaky, then the resulting voltage drop at that point will cause the indicator to glow slightly.

So: what you have to do is check EVERY ONE of these connections for tightness, corrosion, etc. Disconnect every one of them, clean the terminals with a wire brush on a Dremel tool until they're shiny, then reassemble. Make sure the wire connector is a tight fit. Any that are not should be replaced (use only good factory type terminals, not the crap ones from the auto parts store). Don't forget the fuse S11 - clean the fingers and the ends of the fuse. Be methodical! Be sure to disconnect the battery, as all of this wiring is UNFUSED! You don't want arcs and sparks!

The ignition switch will have to be checked with a voltmeter. Measure between the red and black wires with the engine at fast idle. Anything more than 1/2 volt drop here may require an ignition switch replacement.

As a sanity check, disconnect the blue wires at T10 (column 3). Connect a test light between the single blue wire from the regulator and the battery. This light is emulating the dash indicator. It should light up. Now run the engine. The test light should immediately go out. If it does, then you can assume the alternator and regulator are OK, and the problem lies in the wiring described above.
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[MikeyM73]

Telford, thank you very much. That is a big help. I will definitely check things out over the weekend when it isn't raining. Again.

As for ongoing testing, the voltage seems to be ok now, under normal driving conditions, now that the indicator light is working - tested at the battery and confirmed with my dash meter, high 13s to low 14s at idle, lights off; lights on at idle voltage drops to 12.5 / 12.7 but does rise a bit, when underway and RPMs are higher.

In fact, this morning when I started the engine, the light glowed but after driving for a while with lights off, the indicator light went completely out, albeit slowly. Turn the lights on, while driving, the voltage was 12.7 and indicator light came back on dimly.

Still, I will certainly check all connections as you recommend but could this possibly be a weak battery due to the fact that the indicator light hasn't worked for a couple years? Just a thought.

Thanks again,
Mikey
_________________
'73 Pop-top Westy, found sitting in a field for 10+ years, cleaned up, rebuilt furniture, reloved. Original 1.7 block/fully polished crank, 93mm 1.8L balanced AA pistons & cylinders, new 1.8L balanced rods, HAM 42/36 heads, Scat C25 cam & lubalobe lifters, Dual HPMX40s, R2C filters w/ Outerwears pre-filters, functioning thermostat & flaps, Pertronix Flamethrower III, 4-1 exhaust w/ Cherry Bomb 2" turbo muffler & OEM heater boxes, averages about 19-22ish on the highway.