[xj] Intermittent overcharging on '85 XJ6?

HI everybody.
To warm up the discussion again:
I was watching careful the Voltage on my car over the last days and most of the
time it is around 13 on the gauge.
It sometimes goes up to 17 Volt ( Red Sector). The Voltage is usually back to
normal after 5 sec to 2 minutes.
When I recognized this the first time I wasn’t concerned because I had the
manual in mind which is saying as follows:
“With the engine running above idle speed, the pointer (of the gauge) should be
between 13 volts and the top red segment. If the pointer remains in the top red
segment for longer than 10 minutes then the charging rate is too high and the
cause should be investigated.”

It looks to me that Jaguar Cars already expects some wild behavior with those
LUCAS units.
Ten minutes are a long time and I believe my Lucas alternator never reached
that limit. Who knows why it is doing those voltage jumps. I suspected the
battery causing it but everything looks fine so far.
Any suggestions ?

Hartmut 85 XJ6

David A. Snider (ResourceCtr) wrote:> Hmm, I was hoping the ECM had some kind of voltage protection, and this

confirms it. I’m avoiding driving it, though, precisely for the reasons you
cite below. I had checked out the battery and didn’t see any external
damage, but I won’t take any chances!

-----Original Message-----
From: CRossi001@aol.com [SMTP:CRossi001@aol.com]
Sent: Tuesday, October 28, 1997 7:06 PM
To: David A. Snider (ResourceCtr)
Cc: xj@jag-lovers.org
Subject: Re: [xj] Intermittent overcharging on '82 XJ6??

I sure would advise against ignoring this problem. Damage to the ECM and
related sensors most likely will not be a problem, the ECM and sensors are
run off a well regulated 5 volts. The regulators used can usually take
upwards of 40 volts on their inputs without damage. I would be more
with blowing headlights, and other light bulbs. The big damage can come
a battery if it can’nt relieve the excess pressure caused by the internal
heat of overcharging. I have seen a battery that looked like a basketball
after charging for 20 minutes at 18 + volts.