[x300] Odd Charging System Behavior

X300
1

Scrapper has been giving me fits the past week or two, and, worse,
while we’re experiencing a very cold snap here in N Texas.

The first symptom I had was that her oil pressure gauge stopped
working completely (and warning light stuck on). At first I was
terrified somehow oil had leaked out, but checking the stick showed
her full and there were no odd noises going on.

After leaving her parked voer the following 3-day weekend, I went
to start Scrapper that a.m. and there was NO charge in her
battery – not even the dome light would glow. During the
preceding few nights while driving, I had noticed her voltmeter
would sometimes be on ‘‘12 volts’’ rather than the usual 13.5-14 volt
range. It would do this at random and be steady there for a few
miles of driving, despite engine RPMs (although sometimes she would
seem to hot idle at cold idle speeds). The meter would then pop up
to the noraml range. There were no warning lights or check engine
light whenever this happened, btw. This apparently would only
happen when I was driving at night, not during the day.

Thinking for sure the problem had to be the one-year-old Duralast
battery, I had it checked at Autozone and their tester showed it to
be O.K., just completely drained. The tech theorized, b/c I didn’t
leave any lighs on, that I had a ‘‘parasitic drain’’ somewhere in my
system. At this point, I wondered if maybe the bad oil pressure
sender could be draining the battery (grounded?), even with the key
off and out of the ignition. I don’t think though that is
possible, is it?

I had the battery quick-charged by Autozone, put it back in, and
everything seemed normal at first. After a few trips that day, I
noticed the oil gauge/light had started functioning properly once
again, strangely enough. However, on my drive home that night not
only did I have the 12 volt reading thing going on once again, but
could head a mild, steady squalling sound coming from under her
bonnet. This happened all the way home, where, while idling, she
was idling at cold idle speed again. This a.m. she started O.K.
and drove to work O.K. But, tonight driving home, a minute or two
after starting, she went to the 12-volt mode again, and stayed that
way til home, although I heard no squalling this time.

I checked the belts and they are tight, and the alternator shaft
seems tight (i.e. no worn bearing).

Any idea what could be going on here? I’m wondering if having
my headlights on is somehow dragging the system down (a short or
ground?), although switching them on or off and bright vs. dim
doesn’t affect the 12 volt reading. Otherwise, I don’t see why the
problem only seems to happen during night driving.

I just don’t want to go to start my car in the a.m. and have a
totally flat battery again!–
&:slight_smile: Paul '88 XJ6 VDP 138k (black), '96 XJ6 110K (black)
Garland, Texas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

2

In reply to a message from AttyDallas sent Thu 10 Dec 2009:

btw, the oil pressure gauge and light are once again not
working. UGH!–
The original message included these comments:

everything seemed normal at first. After a few trips that day, I
noticed the oil gauge/light had started functioning properly once
again, strangely enough. However, on my drive home that night not

–
&:slight_smile: Paul '88 XJ6 VDP 138k (black), '96 XJ6 110K (black)
Garland, Texas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

3

The brushes in your alternator could be worn out, or you might have a
bad voltage regulator. Get the output of the alternator tested and see
what it does. The oil pressure gauge is a variable resistor, so no
surprises it goes wonky when the voltage is low. I’m pretty sure you’ve
just been driving on the battery alone.

Craig

AttyDallas wrote:>

Any idea what could be going on here? I’m wondering if having
my headlights on is somehow dragging the system down (a short or
ground?), although switching them on or off and bright vs. dim
doesn’t affect the 12 volt reading. Otherwise, I don’t see why the
problem only seems to happen during night driving.

4

In reply to a message from AttyDallas sent Thu 10 Dec 2009:

hi. if I were you I would take off the alt belt, and try to spin
all the components on it se if anything has a bad bearing in it.
also make sure there are no oils on the belt. it seems the battery
is not being charged joe–
jaguarjoe 54 XK 120 rdstr 1961 MKIX 94 XJ6
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5

In reply to a message from pajtas sent Fri 11 Dec 2009:

Thanks, guys … I’ll check all that out …

In the event it’s the voltage regulator, where is it located and
what is a good way to test to see if it is functioning properly?
(I tkae it that it is solid state and not the eletro-mechanical
type, btw?)

I ttied looking at ML’s website to see what the regulator looks
like, but apparently they don’t sell them for the X-300. &:-(–
The original message included these comments:

also make sure there are no oils on the belt. it seems the battery
is not being charged joe

–
&:slight_smile: Paul '88 XJ6 VDP 138k (black), '96 XJ6 110K (black)
Garland, Texas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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6

Hi Paul.

In the event it’s the voltage regulator, where is it located and
what is a good way to test to see if it is functioning properly?

In most late model alternators, the voltage regulator is a replaceable
part of the alternator assembly. It may (or may not) also contain the
brushes. Usually a couple of screws and/or small bolts are all that
is needed to take it out.

The unfortunate part is in some cases you can’t buy just the regulator;
you need to purchase a complete new or rebuilt alternator. I believe
I saw a part number for the Jag regulator when I was looking over the
parts breakdown, but I haven’t yet checked to see if anyone stocks it.

The alternator in my Jag does not charge correctly until the engine
compartment warms up. (Good thing I’m not planning to run it over the
winter here in New Hampshire :slight_smile: I expect it is the regulator, but
I haven’t taken it apart to find out.

As for testing, the easiest way is to have the alternator tested at
an automobile electrical shop. In many cases you can either drive in
and the shop will do what is needed to test the alternator or you may
be able to remove it yourself and bring it in for testing.

  • Mark, 1996 XJ6 4.0
7

In reply to a message from Mark Pilant sent Fri 11 Dec 2009:

Hi Mark,

Yep, I just heard back from our partsmeister Ken Karr @ ML, and
he informs me that the regulator and alt. are an integral unit on
our X-300s, unlike on the earlier XJ40s. I was hoping I could just
r/r the regulator to see if that did the trick, sparing the time
and expense of removing the whole alt.

The downside is the alt assembly is over $300! (and that’s for a
rebuilt one), which is too much $$s for me to take a ‘‘guess’’ with,
as to what is malfunctioning.

I wonder if Autzone can test it for me, in situ? Don’t they have
a tool that clamps onto the terminals of an alt (or has an
inductive pickup?) that can’t tell if it’s charging properly?

Something else I got to thinking about … if the regulator is
bad and diode is stuck open that shouldn’t be, could that be what’s
causing the battery to drain down while sitting (not to mention
flowing from the battery to the alt. instead of the other
way 'round?)–
The original message included these comments:

In most late model alternators, the voltage regulator is a replaceable
part of the alternator assembly. It may (or may not) also contain the

–
&:slight_smile: Paul '88 XJ6 VDP 138k (black), '96 XJ6 110K (black)
Garland, Texas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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8

Hi Paul.

I just checked the CD and the regulator is indeed a separate part.
Here are the numbers:

 JLM11144   3.2, 4.0 & 4.0 supercharged
 JLM11145   6.0

I searched on the part (at least JLM11144) and it seems to be available.

 http://search.waiglobal.com/partnum.aspx?part=IN435

As for testing, you might want to check out an off-road shop specializing
in auxiliary electrical “stuff” (lights, winches, etc.) They might be
able to point you to a place able to test your alternator. Or look up
auto/automotive/automobile electrical in the phone book.

I have an electrical shop fairly close to me, and have had good luck.
Unfortunately, it is a bit too far for you :slight_smile:

Sorry I couldn’t be more help.

  • Mark
9

In reply to a message from AttyDallas sent Thu 10 Dec 2009:

Mine started doing the same thing last winter, sound of a squealing
belt and needle dropping to 12v or so, but not every time it’s
started. Almost always ok until you turn on the lights or put it in
gear. Also did it during the day, and also in warm weather during
the summer occasionally. Once engine heats up goes to normal, or I
get impatient and srep on it and the squealing stops and needle
goes to normal. Bought new belt, but old belt is tight and problem
is intermittant so haven’t changed it yet, wondering if something
is putting a drag on the alternator too. Only had flat battery once
last summer, had been sitting for awhile, never occured to me it
could be part of the above, jumped it and never happened again…

Lee Murray–
The original message included these comments:

preceding few nights while driving, I had noticed her voltmeter
would sometimes be on ‘‘12 volts’’ rather than the usual 13.5-14 volt
seem to hot idle at cold idle speeds). The meter would then pop up
to the noraml range. There were no warning lights or check engine
light whenever this happened, btw. This apparently would only
happen when I was driving at night, not during the day.
only did I have the 12 volt reading thing going on once again, but
could head a mild, steady squalling sound coming from under her
I checked the belts and they are tight, and the alternator shaft
Any idea what could be going on here? I’m wondering if having
my headlights on is somehow dragging the system down (a short or

–
Lee Murray '95 XJS 4.0 Convertible 2+2, and '96 XJ6
Sherburne, NY, United States
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10

In reply to a message from LeRoy Murray sent Sat 12 Dec 2009:

I’ve thought, for peace of mind, about buying one of those gizmos
they sell here in the battery section of the store that plugs into
the cig lighter and shows how much volutage is coming from the
alternator, as well as how many volts are actually in the battery.
It uses red, yellow and green lights to show the condition of both,
as well as actual digital readouts.

Are those things very accurate?–
The original message included these comments:

is putting a drag on the alternator too. Only had flat battery once
last summer, had been sitting for awhile, never occured to me it
could be part of the above, jumped it and never happened again…

–
&:slight_smile: Paul '88 XJ6 VDP 138k (black), '96 XJ6 110K (black)
Garland, Texas, United States
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php –

11

In reply to a message from AttyDallas sent Sun 13 Dec 2009:

I built something similar (with an offset zero meter) to read volts
between 10 and 15V. This was for a Volvo rather than a Jaguar.
However, I don’t belive it will really tell you anything different
than the dash gauge does. Also with the ignition off, is the
cigarette lighter socket still powered?

The squealing is almost certainly the belt slipping. If I drive
through deep water here in the UK, the voltmeter always drops for a
few seconds, followed by a squeal before it comes back up again.
Of course in the UK we are driving on the ‘correct’ side (LHS!) so
water lying at the side of the road gets thrown much nearer the
alternator.

Remember that the belt drive is via the sides of the ‘V’ belt, so
if the belt gets worn, the drive can easily slip despite the belt
being tight.

HTH.

Cheers,
Mike.–
The original message included these comments:

I’ve thought, for peace of mind, about buying one of those gizmos
they sell here in the battery section of the store that plugs into
the cig lighter and shows how much volutage is coming from the
alternator, as well as how many volts are actually in the battery.

–
Mike Stevens, 1996 X300 4.0 Sovereign
Oxfordshire, United Kingdom
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12

Hi Paul.

While a cigar/cigarette lighter monitor might be useful, it may
only tell you half the story. The first issue is you don’t know
what is in the circuit between the alternator, battery and the
lighter. Not the least important of which is the wire gauge used
to connect it all together. As Mike said, it probably isn’t any
better than a (working) dash gauge.

Ideally, you would want to monitor the alternator output as well
as the battery voltage. Of the two, the battery voltage is probably
the more important. The only problem being measuring the battery
voltage in the trunk/boot is not very convenient.

One thing you might do is add a couple of wires which would connect
to the battery and then go into the passenger compartment to be able
to monitor the voltage.

Note, in most cases you will need to be off-idle to get a correct
alternator voltage reading. Most alternators really aren’t charging
at their rated voltage until somewhere in the 1500 - 2000 (engine)
RPM range.

Probably the best thing to have would be an ammeter in-line between
the battery and the rest of the circuitry (except the starting
circuit). If you hook it up (correctly) and see a positive charge,
then it is most likely th case that all is well. However, if it
shows a negative charge (at off-idle speed) it means you are not
charging the battery and it will eventually drain (go flat).

I hope this helps.

  • Mark