When driving I use the ScanGuage scan tool for real-time display of operating conditions, including voltage.
For years the voltage has been right at 14.2 or very close to that. Even when running the a/c, headlights and towing my trailer. It may go down a bit when first turning on an accessory, but then would go back to 14.2 .
I have always done all of my own maintenance on my vehicles.
The a/c had a slow leak and I decided to take my van to "the professionals" to have the system repaired. When I got the van back from them I noticed that the voltage was running around 13.4 and not steady, fluctuating from a max of 14.3 to a low of 11.9. It does not go to 11.9 for long or often. Now, it runs in the mid 13's to mid 12's, fluctuating randomly.
When I left it at the a/c shop it was normal, 14.2, now this??????? I know that my van is getting old and problems will happen. I'm not trying to blame the a/c shop, but what happened?
I know that they removed the battery to replace the receiver/dryer.

1997 E-350 V-10 with 98,848 miles on it.
August 2014 new AGM battery
this week; checked battery connections, looked for other loose connections. No problems found.
Plugged digital multimeter into 12v accessory port on the dash to confirm ScanGauge readings. The voltage readings were close but not always exactly the same. Removed original alternator and had it tested, checked OK.

Any advice regarding this problem is appreciated!

 

Accurately testing the alternator for output voltages is best done ON the alternator, not vehicle body/chassis wiring such as your power point outlet. Those might have connection issues which would cloud any readings.

Your condition sounds like a failing internal voltage regulator which wouldn't be uncommon given the vintage of the alternator, assuming its original to the van.

A competent rebuilder could rehad your existing unit but for me and my money along with wanting maximum reliability I'd go for a new NAPA 130 amp stock-like alternator. About $200, lifetime warranty when I bought one a year or so ago.

If changing out the alternator it would also be a great time checking and possibly replacing the serpentine belt and its tensioner. Then again I like having something dependable and don't mind spending a few dollars to get there!


HTH

 

HTH, Thanks for the advice. Autozone tested my alternator. It passed their quick test, however I'm not sure that a quick test would show the random voltage fluctuations that I see when the alternator is running on the van.
I just checked the voltage on the alternator and on the battery and it is about the same as the power port on the dash. The fluctuation in voltage makes these readings hard to interpret.
It is the original alternator, close to 100k mi. and 18 years old, I'm willing to replace it. Autozone's best replacement with lifetime warranty will cost me $190. Is Napa a better source for an alternator?

Thanks,

RT

 

"HTH" is shorthand for "hope this helps". OTOH I go by JWA here!

I myself tend to avoid Autozone and the rest of those low ball guys in favor of NAPA. I don't know for certain one is better than the other however this lifetime warranty thing is all well and good BUT I don't want cheap parts I'm changing regularly----my time is worth something.

The take away on your readings leads directly back to the internal voltage regulator.

Hope that helps.

 

It is possible that during the repair, the shop did not get the belt tightened properly, causing slippage on the alternator pulley.

But you pulled the alternator and had it tested, and after the re-install its doing the same? Still could be the belt getting old...or glazed, and slipping. Or improper tension on the idler pulley.

When the voltage reading fluctuates, are the dash lights or the headlights also varying in brightness? If so....its fair to assume its the alternator, or regulator, or battery, or some connection between the three, or possibly a bad ground. It sounds like a loose battery connector to me.

If the brightness of the headlamps and the instruments lamps is more or less steady, and there are no check engine lights, and no trouble codes thrown, I would begin to suspect the 12v system thats feeding the dash, and/or the OBD2 port itself. The Scangauge pulls the voltage for operation directly from this port, and also, displays that voltage. I dont believe it 'interrogates' the PCM to determine this voltage, as it does with most other readings.

One more thought. If the system voltage was actually fluctuating that wildly, normally you will get some erratic engine performance...especially during startup.

Let us know what you find.

 

Thanks to JWA and Brian for the advice! I will replace the belt and tensioner. I also want to remove, inspect and clean all connections that relate to the charging system. the battery terminals are clean, bright and tight! I can see many ground and hot wire connections. Any suggestions for connections that may not be obvious?

Thanks,

RT

 

I am also having this issue on my 2000 7.3 diesel. It seems to happen when really hot outside. I was also thinking my alternator was heading south but my batteries stay nice and charged. I have yet to check my alternator connections but, Im leaning towards a wire or lead being loose that reports the output voltage.

 

I'm back to work on my '97 E350.
This is what I have done so far:
Removed, cleaned and inspected all ground cables and straps. Checked OK with OHM meter. Wire brushed cable ends and mounting points and reinstalled. Same for the positive cables. Found nothing loose or corroded. No change in voltage.
Replaced original tensioner and belt (still no cracks in ribs on belt, no signs of glazing). No change.
Installed new alternator. the voltage at the B+ to case on the old alt was 14.25. with the new alt the voltage at the alt is 14.44.

I'm still having a problem with the voltage fluctuating from a max of 14.44 (at alt B+ to alt case) to a low of 11.7 (at idle at the power point on the dash) . Now, it runs in the mid 13's to low 12's, measured at the battery posts, fluctuating randomly. It's about the same measured at the power point on the dash.

I have followed this process for checking voltage:
engine running at 1500 rpm
a/c - on max, front and rear blowers on max (with the blowers on max and the outside temp at 80F to 90F the compressor clutch stays engaged, so I assume that there is a constant current draw from the clutch)
headlights and all interior lights on

I've done a voltage drop test on all grounds and positive cables and found the voltage on the ground circuits to be consistent at most points at .16v. On the positive cable from the alt B+ to the engine compartment fuse box measures .32v. From the info that I have read, both of these are too high. On the positive cable from the starter relay to the fuse box measures .02.
This low voltage and fluctuation began after having an a/c shop replace the compressor.
Could something have changed in the system that is drawing much more current than it was before the compressor change?
What should I check next?

 

Is there a known good battery you can swap in for testing?

Sixto
93 E150 Chateau 5.8 191K miles

 

tabijan, thanks for the idea. I have not tried swapping with another battery. I have had the battery load tested and it passed. The battery is a 750 CCA, AGM and less than one year old.

 

You might be chasing your tail on this one...let me ask again:

Is the brightness of the headlights and/or interior lighting varying or is it steady?

Also, its not unusual to see this type or fluctuating voltage when the alternator is trying to keep up with a fully loaded electrical system.

Under more normal conditions, what are you seeing?

Do you have an analog voltage meter you can attach and watch the needle? Failing that, hook up a simple 12v test light, (not the LED type) and look to see if the brightness of the test light changes at all.

Transient (and normal ) voltage spikes in the electrical system can sometimes fool a digital meter.

 

Repeating my earlier advice the existing alternator's internal voltage regulator needs to be checked by someone with the proper equipment and knowledge to do so.

So far everything you've mentioned points directly to that internal device. Along with having assured connections are in good order there's not much else to cause your symptoms.

 

Yes Brian, I do feel like i'm chasing my tail!
The lights will dim and the blower slows when the voltage drops below around 12.5v.

The voltage dropping below 13v is a new concern.

Normal conditions for this van includes: a/c on, head lights on, towing a trailer with many running lights and battery charging circuit on. I'm not sure of the amp draw for the battery charging on the trailer, it is on a 30 amp fuse. Under these conditions, I'm used to seeing a steady 14.2v on the scangauge with some slight fluctuation.

No load voltage is great! Measured at the alt B+ to alt case at idle = 14.4 to 14.5.
No load voltage measured at the battery posts at idle = 14.2 to 14.4.
No load voltage measured at the power point on the dash at idle = 13.9 to 14.4
No load voltage measured on the scangauge at idle = 13.5 to 14.5.

I have tried adding loads one at at time, headlights on - no change. Headlights off, front blower on max - no change. Front blower off, rear blower on max - no change. I can run two of these three accessories with only a slight fluctuation in voltage. when I add the third accessory, with the engine at idle the voltage will drop to 11.7, sometimes lower.
With the a/c on, both blowers at max, headlights on and the engine running at 1500rpm and above the voltage fluctuates from mid 12's to mid 13's.
This is what I'm chasing.
I'm open to any suggestions on what to check or how to test. I appreciate the advice!

 

JWA, I followed your earlier advice and replaced the original alternator, belt and tensioner with all NEW parts. Measuring at the alt. B+ post to the alt case the no load voltage at idle on the old alt was 14.25. With the new alt the no load voltage at idle at the alt is 14.44.
The problem is only evident when a load is on the system, and voltage is checked at points away from the alternator. The voltage drop that I measure on the alternator harness (B+ to engine compartment fuse box) is .32 when the system is under load, lights and a/c with both blowers on max. I have removed that harness and checked with an OHM meter. It seems OK. It did not have any corrosion on it. I'll change it if there is a GOOD chance that it is causing the problem. $100 at the dealer.
I'm not opposed to changing out original parts for new. I bought this van new in 1996. It has served me well and has been reliable for almost 19 years with just regular maintenance.
Thanks for your help!

 

It seems to all be more or less normal except with the trailer hooked up?

Pull that fuse on the trailer battery charging circuit (or disconnect it) and repeat all the tests and then also, check that trailer battery (volts, water level, connections etc). It could be be pulling close to 30 amps (or maybe more) and loading the alternator down. Its also possible there is an intermittent short to ground somewhere, maybe in the trailer wiring.

Alternators are comfortable putting out half or less of the rated amperage, they can only put out the full rated amperage for a short time.

Its another tail to chase....