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LUCAS ALTERNATOR: From the introduction of the XJ-S until engine number 8S57571, it was fitted with one
Lucas alternator or another -- 66-amp on the pre-H.E., 75-amp on the H.E. There are also reports of Motorola
alternators on these cars, possibly even fitted from the factory. Bob Johnson says the number is A5000/12.
If you’re interested, there is a performance chart for the 75-amp alternator at:
http://www.jag-lovers.org/xj-s/book/Lucas75Aalt.html
If a Lucas alternator seems to be charging intermittently (fully charging one minute, discharging the next as indicated
by the voltage gauge) or has simply stopped charging but has no shorts or burnt wiring, it might be fixable by replacing
just the regulator itself. This is much cheaper than replacing the whole alternator, and is easy to do by removing the
plastic cover from the back of the alternator.
LUCAS ALTERNATOR REPLACEMENT: Below you’ll find several pages on replacing the original alternator with
a GM alternator. Most of these were developed to replace the Lucas alternator -- before Doug Harper broke this news:
“My Lucas 75-amp alternator was suspect, took it to a rebuild shop to see what my options are. He ended up selling me
a rebuilt 1995 Land Rover 110-amp alternator, #13697 Lister or CAE A2051, that was a direct replacement for the 75A
Lucas, just bolted right in. Had to replace the pulley. Made by Marelli!! Using the Radio Shack 270-1509 lighter
adapter to the volt meter trick I was getting 14.2V at 1000 rpm, engine sounded better. The Lucas when working was
putting out 13.66 Volts. The needle now sits 1 bar above mid point, rock solid. 50% more power as a direct
replacement, no bracket required, no messing.”
“The unit has an internal fan, same hole locations for bolts, and appears to be volume-wise smaller. Beside the power
out and sense lugs is a timing output pin for diesels (?) and a 12VDC secondary power source on some units. The first
one they showed me had cracks in the metal housing where the regulator bolts connect, on all 3 bolts, one serious. The
second one they showed me was perfect - well, almost, but no cracks. Make sure you want the crack-free units.”
Frankly, if you’re replacing a Lucas alternator for any reason, you’d be well advised to go ahead and upgrade to this
Land Rover/Marelli alternator even if you don’t need the power. It’s one of those “couldn’t hurt” kinda things.
You probably should upgrade the power cables as described on page 579.
BOSCH ALTERNATOR: Beginning with engine #8S57572, the XJ-S was fitted with a Bosch 115-amp alternator.
This alternator is driven by a multi-groove belt instead of the V-belt found on earlier cars. Since the alternator is driven
from the crank damper itself rather than from the pulley that bolts onto it, this change involved the replacement of the
earlier crank damper C36013 with one with the multi-groove pattern, EAC9248 (replaced sometime thereafter with
EAC9693 to fit a timing disk for the Marelli ignition). The pulley part number didn’t change.
ALTERNATOR LOAD DUMP MODULE: Reportedly, the 115-amp alternators fitted to the late 80’s XJ-S will not
begin to charge until the engine has been revved up. Although not really a problem, it is somewhat irritating to see the
charge light on when everything else seems OK. According to Michael Neal: “Actually, there is a fix for this. There is
a device called an alternator load dump module that was fitted to the later XJ40’s and XJ-S’s with the high output
alternator. Fitting the module will fix the problem. The load dump module will cause the alternator output to function
properly at idle without having to raise the idle speed.” The part number for the 115-amp dump module is DBC 5896.
NOISY ALTERNATOR BELT: If you have the later Bosch 115-amp alternator with the multi-groove belt, chances
are that sooner or later you will have trouble with that belt squealing. Neither tightening the belt nor even replacing it
will help for long. The problem here is a flaw in the design of the multi-groove pulley -- not just this one on the Jag,
but basically with all multi-groove pulleys. The author discovered this design defect on his ’84 Honda Accord (his ’83
XJ-S has V-belts), but the problem has been confirmed on the later Jaguars as well.