Ford pickup low voltage at idle

I think I posted about this before, but never really got beyond two
suggestions...

Problem is this. When truck is idling, if enough accessories are turned
on, voltage will start to drop, and keep on dropping as if the battery
is discharging. Voltage at battery with key off is about 12.9 (seems
high?) with engine running about 14.0, with lights, A/C and fan on
starts off at about 12.8 and keeps steadily dropping. If you rev up the
engine with all the accessories on eventually the gauge will snap back
up to the normal position but will fall off again when the engine
returns to idle. It is almost like a regulator issue, the needle moves
all at once and too smartly for it to be just voltage falling off
because the RPMs are too low.

Suggestions made were a) battery may be bad? I doubt it as voltage
seems high with key off. b) connector to alternator is bad? possible
but alternator itself is too hot to touch after only a few minutes of
idling. FLAPS says alternator tests OK. At this point I feel like I
should take it to a good auto electrical expert to check the whole thing
out, but I have absolutely no idea where to find one. Any ideas of
anything else to check? BTW I also checked for a voltage between
alternator case and B-, ground wiring appears to be OK even under heavy
load.

Where is the voltage regulator for this truck? Is it integral with the
alternator (and therefore should have been tested when the FLAPS spun it
up) or is it hidden elsewhere?

This is a '93 F-150 with the 4.9L engine. If I can get this issue and
also a cold start issue fixed it'll be darn near done.

thanks,

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

You have shorted diodes in the alternator.

Nate Nagel wrote:
>
> I think I posted about this before, but never really got beyond two
> suggestions...
>
> Problem is this. When truck is idling, if enough accessories are turned
> on, voltage will start to drop, and keep on dropping as if the battery
> is discharging. Voltage at battery with key off is about 12.9 (seems
> high?) with engine running about 14.0, with lights, A/C and fan on
> starts off at about 12.8 and keeps steadily dropping. If you rev up the
> engine with all the accessories on eventually the gauge will snap back
> up to the normal position but will fall off again when the engine
> returns to idle. It is almost like a regulator issue, the needle moves
> all at once and too smartly for it to be just voltage falling off
> because the RPMs are too low.
>
> Suggestions made were a) battery may be bad? I doubt it as voltage
> seems high with key off. b) connector to alternator is bad? possible
> but alternator itself is too hot to touch after only a few minutes of
> idling. FLAPS says alternator tests OK. At this point I feel like I
> should take it to a good auto electrical expert to check the whole thing
> out, but I have absolutely no idea where to find one. Any ideas of
> anything else to check? BTW I also checked for a voltage between
> alternator case and B-, ground wiring appears to be OK even under heavy
> load.
>
> Where is the voltage regulator for this truck? Is it integral with the
> alternator (and therefore should have been tested when the FLAPS spun it
> up) or is it hidden elsewhere?
>
> This is a '93 F-150 with the 4.9L engine. If I can get this issue and
> also a cold start issue fixed it'll be darn near done.
>
> thanks,
>
> nate
>
> --
> replace "roosters" with "cox" to reply.
> http://members.cox.net/njnagel

--
Mike Walsh
West Palm Beach, Florida, U.S.A.

On Aug 5, 3:13 pm, Mike Walsh > wrote:
> You have shorted diodes in the alternator.

Shorted diodes would drain the battery when the engine is shut
off. He made no mention of that. An open diode might be possible, but
my bet is on worn-out alternator brushes that aren't making good
contact anymore. It's the most common alternator problem. Brushes
should be checked every so often, like maybe 50,000 miles or so. We do
them at 500 flying hours in our aircraft, and they are Ford
alternators. They don't go beyond about 1,000 hours without being
short enough to need replacement. 1,000 hours at an average speed of
40 MPH would be 40,000 miles.

Dan

On Aug 6, 1:23 pm, wrote:
> On Aug 5, 3:13 pm, Mike Walsh > wrote:
>
> > You have shorted diodes in the alternator.
>
> Shorted diodes would drain the battery when the engine is shut
> off. He made no mention of that. An open diode might be possible, but
> my bet is on worn-out alternator brushes that aren't making good
> contact anymore. It's the most common alternator problem. Brushes
> should be checked every so often, like maybe 50,000 miles or so. We do
> them at 500 flying hours in our aircraft, and they are Ford
> alternators. They don't go beyond about 1,000 hours without being
> short enough to need replacement. 1,000 hours at an average speed of
> 40 MPH would be 40,000 miles.
>
> Dan

Is this an alternator where there's a bearing and brush kit readily
available at my FLAPS or do I need to actually send it off to be
professionally rebuilt? I have perfect confidence in my ability to do
the work, but in some cases (e.g. Bosch) I have been unable to source
the parts through consumer-level channels.

nate

On Aug 6, 3:16 pm, N8N > wrote:
> On Aug 6, 1:23 pm, wrote:
>
> > On Aug 5, 3:13 pm, Mike Walsh > wrote:
>
> > > You have shorted diodes in the alternator.
>
> > Shorted diodes would drain the battery when the engine is shut
> > off. He made no mention of that. An open diode might be possible, but
> > my bet is on worn-out alternator brushes that aren't making good
> > contact anymore. It's the most common alternator problem. Brushes
> > should be checked every so often, like maybe 50,000 miles or so. We do
> > them at 500 flying hours in our aircraft, and they are Ford
> > alternators. They don't go beyond about 1,000 hours without being
> > short enough to need replacement. 1,000 hours at an average speed of
> > 40 MPH would be 40,000 miles.
>
> > Dan
>
> Is this an alternator where there's a bearing and brush kit readily
> available at my FLAPS or do I need to actually send it off to be
> professionally rebuilt? I have perfect confidence in my ability to do
> the work, but in some cases (e.g. Bosch) I have been unable to source
> the parts through consumer-level channels.
>
> nate

Forgot to mention, if they fail for you at appx. 1K hours, they
probably are toast as vehicle has about 140K miles and no record of
alternator having been touched (PO kept good records, I have a
surprising amount of documentation)

nate

On Aug 6, 1:16 pm, N8N > wrote:
> On Aug 6, 1:23 pm, wrote:
>
> > On Aug 5, 3:13 pm, Mike Walsh > wrote:
>
> > > You have shorted diodes in the alternator.
>
> > Shorted diodes would drain the battery when the engine is shut
> > off. He made no mention of that. An open diode might be possible, but
> > my bet is on worn-out alternator brushes that aren't making good
> > contact anymore. It's the most common alternator problem. Brushes
> > should be checked every so often, like maybe 50,000 miles or so. We do
> > them at 500 flying hours in our aircraft, and they are Ford
> > alternators. They don't go beyond about 1,000 hours without being
> > short enough to need replacement. 1,000 hours at an average speed of
> > 40 MPH would be 40,000 miles.
>
> > Dan
>
> Is this an alternator where there's a bearing and brush kit readily
> available at my FLAPS or do I need to actually send it off to be
> professionally rebuilt? I have perfect confidence in my ability to do
> the work, but in some cases (e.g. Bosch) I have been unable to source
> the parts through consumer-level channels.
>
> nate

I'd get the part number off that alternator and go see if your
parts supplier has some brushes. Bearings, too, are a good idea. If
the slip rings in the alternator are chewed up they'll need turning on
a lathe. Otherwise, they should be cleaned up with a bit of fine
sandpaper and polished with Scotchbrite. They get oxidized, which
represents resistance, so that the field current can't reach maximum
and the alternator's output falls off.

Dan

wrote:
> On Aug 5, 3:13 pm, Mike Walsh > wrote:
>
>>You have shorted diodes in the alternator.
>
>
> Shorted diodes would drain the battery when the engine is shut
> off. He made no mention of that. An open diode might be possible, but
> my bet is on worn-out alternator brushes that aren't making good
> contact anymore. It's the most common alternator problem. Brushes
> should be checked every so often, like maybe 50,000 miles or so. We do
> them at 500 flying hours in our aircraft, and they are Ford
> alternators. They don't go beyond about 1,000 hours without being
> short enough to need replacement. 1,000 hours at an average speed of
> 40 MPH would be 40,000 miles.
>
> Dan
>

You called it, I called my FLAPS at lunch today, they said they needed
to know which alternator I had to say whether or not they had parts for
it, so I pulled it when I got home from work (good thing I'd done it
before, because it's about 95 degrees out, had to wrap a bandanna around
my head to keep my glasses from getting sweated on, and I was getting
eaten by skeeters) took it into the garage, started to take it apart,
brushes are nubbins. Unfortunately FLAPS does not carry brushes for the
one I have (75A) I'm on hold with Crap Boys right now...

I'd rather throw new brushes into the original than pay $80 for a reman
of dubious quality. the other option is to pay the $$$$$ to have it
gone through by the local rebuilder, but they are in Annapolis which is
about 50 miles away, not open on Saturday, and pricey...

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

Nate Nagel wrote:
> wrote:
>
>> On Aug 5, 3:13 pm, Mike Walsh > wrote:
>>
>>> You have shorted diodes in the alternator.
>>
>>
>>
>> Shorted diodes would drain the battery when the engine is shut
>> off. He made no mention of that. An open diode might be possible, but
>> my bet is on worn-out alternator brushes that aren't making good
>> contact anymore. It's the most common alternator problem. Brushes
>> should be checked every so often, like maybe 50,000 miles or so. We do
>> them at 500 flying hours in our aircraft, and they are Ford
>> alternators. They don't go beyond about 1,000 hours without being
>> short enough to need replacement. 1,000 hours at an average speed of
>> 40 MPH would be 40,000 miles.
>>
>> Dan
>>
>
> You called it, I called my FLAPS at lunch today, they said they needed
> to know which alternator I had to say whether or not they had parts for
> it, so I pulled it when I got home from work (good thing I'd done it
> before, because it's about 95 degrees out, had to wrap a bandanna around
> my head to keep my glasses from getting sweated on, and I was getting
> eaten by skeeters) took it into the garage, started to take it apart,
> brushes are nubbins. Unfortunately FLAPS does not carry brushes for the
> one I have (75A) I'm on hold with Crap Boys right now...
>
> I'd rather throw new brushes into the original than pay $80 for a reman
> of dubious quality. the other option is to pay the $$$$$ to have it
> gone through by the local rebuilder, but they are in Annapolis which is
> about 50 miles away, not open on Saturday, and pricey...
>
> nate
>

Spoke too soon. (don't know why my previous message is timestamped
9:15; I actually composed that maybe 2 hours ago.) I found a local-ish
parts store with brushes, bought 'em, installed 'em, they work and I
certainly feel better about the alternator now that there's some actual
spring tension holding the brushes against the slip rings, but I still
have the same problem exactly as described above, alternator is still
very hot too. Any ideas?

I did not completely disassemble alternator, just removed the black
plastic piece that holds the brushes (is that the regulator?) and
cleaned the slip rings. The rear slip ring was a little worn looking
but I was in a hurry and don't have air tools so I didn't completely
disassemble to clean it up. I did wipe them clean with solvent so it
should be mostly OK.

I too don't think it's diodes; truck regularly sits 2-3 days at a time
with no apparent discharge. Didn't have to jump it when I went to test
drive it either, and who knows how long it was sitting then. I don't
recall if I tested for key off current draw but I don't feel like trying
it now, because it's freaking hot outside and I'm sitting in my nice
(relatively) cool basement typing this. And it's late and I haven't had
dinner yet, which makes me cranky

thanks,

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

"Nate Nagel" wrote

> I found a local-ish
> parts store with brushes, bought 'em, installed 'em, they work and I
> certainly feel better about the alternator now that there's some actual
> spring tension holding the brushes against the slip rings, but I still
> have the same problem exactly as described above

You do realize that just as engines don't put out maximum HP at idle,
alternator's don't put out max amps/volts at idle either. If you're not spinning
the alternator fast enough to keep up with whatever load you put on it, no
regulator or brush set in the world is going to help.

Have you tried doing a LOAD test with a load tester?
A battery could have 12V and just enough AMPs to start the engine yet
is unable to keep up with the amp draw being uses Vs., what the
alternater can recharge. I have seen may batterys be so dead it will
not even light up a marker light and yet have 12V.


--
Calgary ZR2
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