Well, Superblack’s battery not only went dead on me as it did the other day while I had the door open for awhile, it did the same thing to my tech bud yesterday. We know it’s not the battery (which is brand new) so apparently the car’s voltage gauge was in fact operating properly when it showed it below 12 volts while idling. Checking the charging at the battery clamps showed at idle a charge coming in from the alt. of only 11 volts. Worse, the incoming amperage was only 27 or so amps. Since the belt seems nice and tight, seems the only thing that could be going on is a bad alternator. Everyone agree as to that conclusion?
Good news is the rebuilt alts for the 5.3 are only $135 at two local suspects (plus core charge). My tech isn’t too happy b/c he thinks r/ring it is a bit involved, but I looked at the factory service manual directions and actually it seems pretty simple to me, even simpler than that for the 4.0s (go figure ) … He seems to think that the air injection pump has to also be removed to get at the alt. (and two belts), but the manual doesn’t seem to indicate that. ?
If the battery voltage is down at 11V with 27A going in to it that might be just what you expect at low engine RPM. If you increase the RPM you should get more amps and a higher voltage around 14V.
Even brand new batteries can be faulty.
Well, to be sure, I’m going to use one of my A.A.A. service calls and have the mobile tech come out on Saturday. A.A.A. told me they have the proper devices to check both the battery and alternator functioning … We should know then for sure what is going on … The one thing I can’t figure out is that, per the factory workshop lit., whenever the charging voltage drops below 12 volts that should trigger the red warning light on the indicator strip, which has not happened (and yes, the bulb is good).
Have you checked the circuit end-to-end? I’ve had the indicator wire from the alternator fail internally making it seem like there isn’t a problem. It also stops the energisation of the coils at low revs. If you are getting something out of the alternator, I would guess that the diode pack has gone bad. Should be easy to get replaced, but have them do the bearings as well.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
8
There is a Marelli alternator for a Range Rover that’s a bolt-in replacement for the 75A Lucas. More amps, newer design.
Well, I got home last night and my tech bud had the battery back on the charger, as it was dead again. Again, assuming my new battery is not a dud, seems like something is amiss in the charging circuit. My tech said he noticed this time that it almost seems like the car is “fighting” charging - i.e. whenever the RPMs are increased the voltmeter gauge reading actually DECREASES (i.e. going even further below 12 volts) … wth??? That’s making me wonder if the real problem is the voltage regulator. However, IIRC, on these 115 amp Bosch units the regulator is the integral type (i.e. part of the alternator). If so, then the only solution is to replace the alternator still.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
10
Ignore the fascia guage. Use the voltmeter you got from HF!! Read battery volts, engine off. Repeat with engine at idle. Repeat with engine at about 2000 rpm. Compare the numbers.
OTH!!! A completely flat battery in a sort time. can mean one or both of two things:
Bad battery, internal short.
Bad diode in the alternator. A diode allows volts to flow only one way, alternator to battery.in this application. If it goes bad, then battery volts will flow to the alternator. That will continue as the engine is off til thee battery is “dead”.
A few of these backwards cycles and the battery will be a goner…
Not familiar with that engine and it’s accessories. But, it may be feasible to drop the alternator from below…
Worse, the incoming amperage was only 27 or so amps. 
Since the belt seems nice and tight, seems the only thing that could be going on is a bad alternator. Everyone agree as to that conclusion?
) … He seems to think that the air injection pump has to also be removed to get at the alt. (and two belts), but the manual doesn’t seem to indicate that. ? 
That’s making me wonder if the real problem is the voltage regulator. However, IIRC, on these 115 amp Bosch units the regulator is the integral type (i.e. part of the alternator). If so, then the only solution is to replace the alternator still. 