A note to inform fellow X300 owners that before you condemn
your battery, starter or alternator as being the problem with
starting/charging, I have a very easy check and fix.
Background: (apologies for the long winded description):
When I bought the XJR about 18 months ago, the previous owner
told me he was having starting problems which the local Jag dealer
tried (at great expense) to sort out. They replaced battery,
starter and alternator (as they would, eh). It did appear to be
fixed at first but when I bought it I was not too hsppy about the
charging voltage of between 12.9v & 13.5v. Normal charging voltage
irrespective of load is between 14v to 14.5v. This is the correct
range btw as the voltage regulator in alternator’s ensure a steady
voltage output irrespective of the load on a battery.
Recently she began to have hit and miss starting problems i.e.
the starter solenoid pulled in but engine would not turn over
despite a recently charged battery showing 12.5volts (without load)
and running charge voltage of anywhere between 13-13.5v (used a
multimeter rather that the car’s voltmeter) Anyway before I
resorted to replacing expensive parts, I decided to look at the
wiring diagram to determine the starting & charging circuitry and
discovered that the main cable from the starter terminal (to which
the alternator output is also connected to) was routed thru the
engine bulkhead into the car cabin using an insulated brass
terminal post/pillar to connect to the heavy cable going thru the
car itself to the rear mounted battery. I wondered if a high
impedance (resistance) was occuring at this point, so to prove it I
started the car (thank God it did this time) and used a long heavy
jumper cable to connect this + terminal in the engine bay side
directly to the + terminal of the battery. Instantly the voltmeter
rose from 13.2volts to 14.5volts. I dismsntled the terminal, which
on a RHD car is located on the bulkead inside the engine bay
adjacent to the autobox dipstick tube. Very easy to get at. I
discovered that the steel nut under the cable lug was totally
rusted, that the copper coated steel washer was extremely dirty and
that the underside of the main steel nut was corroded. Cable lug
also was dirty but cleanable. Jaguar in their infinite wisdom uses
steel nuts with only one copper plated steel washer on a brass
threaded stud, which is totally incorrect for high current DC
current application’s.
After cleaning the cable lug, wire brushing the brass threads on
stud, using M8 Brass nuts and proper copper washers under bottom
nut, above this nut, then cable lug, then another copper washer and
finally an M8 Brass nut, I tightened the whole lot nicely. Applied
some grease on assembly. All my starting and charging woes
disappeared instantly. Took me 10 minutes to do this.
Summary:
Before you condemn your battery, starter or alternator, first
check this bulkhead terminal for corrosion.
Cheers and hope this helps others
Martin–
martin mcgovern
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