I am still being left stranded after parking. Car starts right up when jumped.


I started by cleaning battery cable grounds, adding a ground from the inside of the r/h wheel well bolting the cable to an unused bracket in front of the R/h Front Shock and reading past posts on alternator problems.


I was finding that the voltmeter needle would stay at the bottom of 13, regardless of charge. I was not having a battery charge light, it would go off after starting the car.


A half hour or so after shutting off the car, the starter motor would engage, but not have the juice to turn over the engine.


I pulled the instrument cluster and cleaned the grounds and all connections on the printed circuit where the two connectors plug in. The 90 still has the four barrel gauges. I changed the bulb for the battery light as well.


Now the voltage needle is at the top of 13. When I check voltage at the battery before starting, Battery is 13.04 or 13.06 VDC. After starting, voltage at battery is 13.40 up to 14.68, so the Bosch alternator is now charging.


However, I am still having the same problem. I changed the starter motor to a gear reduction unit. Still have the problem. I checked for battery drain by disconnecting the negative lead at the battery and measuring milliamps with black lead to battery negative post and red positive lead to the negative battery cable. I got 0.06 amps, which seems to be below the 50 milliamp max suggested limit to avoid battery drain.


I changed batteries.


I am putting the car on Jack Stands and loosening the engine mounts and jacking up the engine so that I can get at the engine to subframe ground strap. I am missing something, but don't understand what.

 

Excuse this rather obvious point, but just in case you have not checked it, are you 100% sure the boot courtesy lights are being switched off by the switch in the front LH top corner of the boot when the lid closes? Place a rubber pad on the boot lid where it pushes the switch if you are not sure.

Second, have you a burglar alarm type device on the car?

Third, re-test for a drain by disconnecting the positive feed cable from the battery and repeat the test.

Finally, try disconnecting the alternator charging cable at the alternator end, and see if that stops the drain.

greg

 

What is the voltage reading when setup the same as your amp test (reading between the negative post and cable) and how does it compare to the reading between the two posts?

So at 13.04 it won't start the car?

 

I am assuming you mean the battery voltage is 13V but the car will not start.

What size battery do you have. The V12 needs 600CCA and 13V will start the car. 200CCA and 13V will NOT start the car.

Greg is right on with the boot lights.

 

Right now I have a Duralast Platinum with 750 CCA @ 0 degrees F.


I installed it replacing an Optima Red Top model 25 with 910 CA and 720 CCA.


I still have both.


The problem with these gel cell batteries is that you can't check with a hydrometer looking for a low cell specific gravity compared to the other cells.


I repeated the test for drain on the positive post as requested. With the positive lead touching the positive battery post and the negative lead touching the positive cable with the cable disconnected from the battery, reading was 0.06 ma. Reversing the meter probes with the negative probe to the positive battery post and the positive probe to the positive cable, reading was 0.02 ma. No difference between these results and the earlier test on the negative battery post and cable.


I have the trunk (boot) light switch disconnected with lights off.


Reading battery volts before connecting cables, battery read 13.22 volts. After starting, voltage read 14.32 v with engine running. After driving 20 minutes, voltage at battery with engine running was 13.84 v. Leaving battery connected and shutting off engine, voltage was down to 12.90 v after 20 minutes and car would not start.


Hooking up the now spare Optima with jumper cables and 13.08 v at the Optima, car will not turn over.


With ignition in position 2, ABS pump runs, Fuel pump runs, A/C (in off position) blower cycles (?) a few seconds as it normally does and is off. Turning key to start position, starter relay clicks and starter engages but won't turn over engine. Disconnecting neg batt cable and charging battery for 5 min, hooking up cable and car starts.


A friend thinks the alternator field is staying energized. He suggests placing a wrench against the back of the alternator with engine off. He says that if the field is energized, the alternator behaves like an electro-magnet and wrench will stick. He also suggests disconnecting battery, disconnecting the cable from the alternator to the starter, insulating the end of the cable, connecting the battery and waiting the 20 minutes and then attempting to start the car.


All of this brings me back to the Load Dump Module for the Bosch Alternator. The 1990 wiring diagram depicts the module as two parallel resisters each with a diode in series. If what I read on testing diodes is correct, Attempting to read continuity with meter probes will read continuity one way, but will not read if the meter probes are reversed. If the diodes are faulty, continuity will be read in both directions.


I will perform the alternator test my friend suggested and report back.

 

I forgot to mention that I have no alarm system. I have installed electric fans, but have a switched relay to shut the fans off whenever ignition is off. I have had the fans for about two years and the drain is just in the last few months.

 

With the battery cables disconnected you are not checking for quiescent current drain. You need to install the meter between one battery terminal and the battery. put meter on mA



14.32V when running indicates the battery is fully charged, 13.84v indicates the battery is charging.

Measure the voltage at the starter motor, I suspect this will be a lot less than at the battery. Your car should start (JUST) with 12.9v. If so clean the terminals on the starter and the positive and negative posts on the firewall, and the engine earth straps.


No necessarily large diodes are difficult to test with a meter as the breakdown voltage is higher than most meters output, so if the diode is leaky (very common) this test will not tell. You need to put them on a variable power supply and measure the current and voltage both directions. If you do this test BE CAREFUL with the voltage, especially in the reverse direction, if the voltage goes over the max reverse the diode will conduct suddenly and go BANG.

If those diodes were faulty I would expect your alternator would not be charging at full current, you can check this but will need a current clamp capable of 100amps, charging current on a low battery should be 30-40amps

 

I had a starter problem about six months ago and replaced the Bosch small diameter starter with one of the aftermarket gear reduction starters. After a few months the problem started.


I kept assuming that the reason for the car not wanting to start after 10 - 15 minutes was a battery drain. Why it would start with Jumper cables (usually took 40 minutes or so for the Mrs. to arrive) I don't know.


But I let the car set about 3 hours and, lo and behold it started right up. I just installed a rebuilt Bosch small diameter starter and have not had any trouble since.


So, it seems the gear reduction starters don't like the heat from the Catalytic converters on the 90 XJS.


The take away is that you need to let the car cool and verify that the battery is really drained and that the starter is not reacting to heat.

 

Mikebaker3,
I have been watching this thread and was wondering why you were having this problem. I too was wondering what voltage you had at the starter. Just glad you figured it out.
Happy Holidays!
Jomo