I have a XJ8 basic with 4.0 V8. I have been having issues with keeping my battery charged up while I am driving. I have changed my alternator and I still have the problem with my battery keeping a charge. I also have changed my battery as well. Please I need some guidance on this issue. I have been told that it has another voltage regulator other than the one in the alternator. Oh if you could please let me know where I can get an manual on this car.

 

Welcome to the forum. In the Sticky's at the top of the forum page you will find instructions on downloading JTIS 21 by jimlombardy. That is the factory manual. It is difficult to navigate at first, but everything is there, including wiring diagrams.
I am not sufficiently familiar with the charging system to offer assistance, but I am sure help will arrive soon.

 

It's interesting that this problem has arisen just as it seems I'm encountering the same problem with my car.

When I had the battery recharged, I received several pieces of information from the mechanic, none of which I am certain about, but several of which would certainly help in diagnostics. His comments were:

1. If all of your lights, electronics, etc., appear to work as usual when the car is running it's unlikely that there is an alternator problem, per se.

2. If the battery keeps discharging, but the alternator tests OK, disconnect your negative terminal when the car is not running to see if this stops the discharge. This is particularly helpful if the discharge is occurring rapidly, like overnight or over two or three nights.

3. If #2 cures the rapid discharge problem, suspect the relay that's part of the charging system has gone bad or intermittently bad. He commented that when this happens it is virtually impossible to detect by most typical "hook it up and check it" diagnostic methods. It's by trying the above that you can trace it down.

Perhaps another poster can chime in on the validity (or lack thereof) in the above. I have never been great with electrical stuff and can use all the help and suggestions I can get.

 

@Robert and Brian,
Before you guys start throwing good money after bad, try a few simple checks.

Measure the voltage at the battery before starting, above 12.5V Ok.
Measure the voltage at the battery after starting, around 14.1V Ok.

If the second one is Ok then you most likely have a parasitic drain on the the battery and that can be tricky to track down, but there are a few usual suspects.

Also here is the Jag way to test the battery:-

The Jag procedure to check a battery is:

Before carrying out an open circuit voltage check, you must ensure that there is no battery surface charge present. The battery may be tested either on a bench or on the vehicle. A vehicle which has had its battery charged or been driven within 24 hours prior to the test must have its surface charge removed using one of the following methods:

- Wait 24 hours before the test is performed.

- Or switch on the headlights on main-beam for 5 minutes

Open circuit voltage test (Multi-meter connections)
Battery voltage should be measured after 10 minutes has elapsed following surface charge removal. Connect the red positive lead of the digital multi-meter to the battery positive terminal post and the black negative meter lead to the negative battery terminal post, (with no additional loads present and engine stationary).

Compare your results and carry out the recommended actions accordingly, as shown below.

Open circuit voltage ~ 12.45 volts or less
Unsatisfactory result: See note above and carry out a full diagnostic routine. Fit replacement battery.
- Scrap or return removed battery.

Open circuit voltage ~ 12.45 to 12.49 volts
- Remove and re-charge battery.
- Carry out another post-charge check
- If the result after charging the battery is 12.49 volts or less then fit a replacement battery.
- Scrap or return removed battery.

Open circuit voltage ~ 12.5 volts or above - Satisfactory Result

Next, a garage/auto-electrician should have the equipment to be able to carry out a High Discharge Rate Test as follows:

Connect the high rate discharge tester as follows:
- Remove the battery from the vehicle and take off cell tops (during this test observe cells for excessive gassing and bubbling from individual cells indicating a potential faulty cell).

- Connect the tester's red lead to the positive and the black lead to the negative battery post.

- Set the current at 210 amps for in service vehicles and in service batteries.
- The voltmeter should read 9.6 volts or above after 15 seconds have elapsed.

The battery must be charged after this test.
If the voltage is 9.6 volts (or greater) at 20°C (or greater) throughout the 15-second test period, then the battery is serviceable. (9.5v @ 15 deg, 9.4v @ 10 deg,9.3v @ 4 deg)

Try the simple checks first and we can go from there.

Hope this helps,

 

Jim,

Thank you for your reply. Here's a bit more hard data on my situation. The previously posted comments were after the battery had been hooked up to one of those high-tech charging-checking stations for about 2 hours going through whatever voodoo that they do. The results were "Good Battery:"

Rated: 900 CCA Measured: 878 CCA
Voltage: 12.58
Elapsed Time: 1:30:00
Amp Hours: 43.5

Now, mind you, I had the unusual circumstance prior to all this of having the car sit for about 1 week to a week and a half, but have never had battery issues like this after doing so when on vacations before. Driving the car for relatively short (not 1 block, but less than 20 miles) would seem to improve the battery *very* slightly, but even if the car sat an hour or two things would seem to be pretty much at miserable baseline.

I'll grab my multimeter and do the tests you indicated in a short while and post the results.

Brian

 

Do some searching here. The biggest weak points are the engine ground strap and the false bulkhead connector. Both will cause poor charging/starting/no starting, even with a good battery.
Measure between the engine block and the chassis with the engine running, you shouldn't get more than 0.1-0.4 volts, any more than that and the ground strap is bad.

Check this thread- https://www.jaguarforums.com/forum/x...esolved-84962/

 

To follow-up I did measure the battery voltage after the car had been sitting in excess of 24 hours.

The initial voltage is 12.05, which is consistent with what my multimeter reads on the batteries on other cars "in the fleet."

However, when the car is running I get only 12.85V on the Jag while I get over 14V on my Buick.

What should I check next? Probably the alternator has gone bad after 153K miles, but, I await the voices of experience for other suggestions.

 

Hi Brian,
Looks like you may need to change the alternator. The one you have may be repairable but it may be more cost effective to change it.

 

Where did you measure it from? At the battery it may be low, but measure from the false bulkhead to the engine block, or throttle body, when it's running, and see what the voltage is.

 

I did measure at the battery. When the multimeter probe is initially touched to the battery terminals it very quickly flashes something above 14 volts but then almost immediately settles down to 12.85. This is in contrast to my Buick where it reads above 14V from the moment you touch the battery terminals when the car is running and stays there.

If you happen to have a photo that shows the points that you'd like for me to use as alternates, please post it. I am not quite certain what the false bulkhead is.

 

I'm out right now so I don't have access to my pictures, but if you look at the threads that I linked to earlier, you can hook up your meter from the throttle body has shown in one picture and the shock tower bolts as shown in the other picture. With the engine running you should get a voltage reading. If your ground strap is okay it will be less then one tenths of a volt. If you get a reading of 1 V or more, then you have a problem with the grounding strap.

 

I'm doing this from my iPhone, and it doesn't always understand my dictating. Your reading should be I would say less than half a volt would be acceptable. .2 V .3 maybe but if it's up towards 1 V were more you definitely have a problem.

 

Well, the reading between the throttle body and shock tower bolt is well under 1V. The reading at the battery when the car is running is still under 13V.

I think my relationship with this car may soon be coming to an end. It's been a great car but at 15 years old and over 150K miles it's developing more issues than I care to keep up with.

 

Well this is new to me but I will give you my opinion for what it is worth. After reading all of the comments it is my opinion that you either have a bad alternator or a bad ground at the alternator. Any automotive parts shop should be able to test the alternator for you they simply run the alternator up to speed and short the ground terminal on the alternator. The output should go to 14.5 volts. If it doesn't the problem is in the alternator if it does you now know that your problem is a grounding issue follow the ground wire from the alternator to a solid ground. Check all connections for corrosion or broken wire. Hope this helps.

 

I had a problem with the braided ground strap at the battery. Just sayin'. Car would not start, would not jump, touched the negative battery terminal and it was smokin' hot. I replaced the cable with a heavy generic solid one. The other ground points are also good suspects for a bad connection, as mentioned. The one at the false bulkhead is a common spot for problems. I would go over them with a fine tooth comb before buying an alternator.

 

One Monday Morning went to start the Jag and no lights, horn or anything. Placed my battery charger on it and it started right up. I had not driven for two days. Two weeks later the same things happened and it started right up. Today, left work, parked went in the store, once again, nothing. AAA came and gave me a boost and it started right up,. he said the alternator looked good and the battery was holding the charge. Got home and cut it off and it started right up/ What could possibly be causing this? HELP!!!!!

 

Hi PAJ,

One possibility is that high resistance due to corrosion on battery power connections and/or ground points is causing poor battery charging. Cleaning these connections every few years, or whenever you're performing maintenance near any of these connections, is a good way to help reduce the occurence of these sorts of gremlins.

I am attaching pages from the Electrical Guide that show the battery power connections and the ground connections throughout the car. Disconnect the battery (both the negative and positive cables if working on battery power connections). Remove the nut from the battery power connection or ground stud, lift off all the wire eyelet or ring terminals and note the position of any star washers. Clean the threaded stud, wire terminals, nut and washers with a small wire brush and zero-residue contact cleaner spray. Allow to dry and reassemble. Ensure that the nut is tight but not too tight, as some owners have accidentally broken the studs off.

A few good places to start would be the power connections at the alternator and starter, the engine ground strap, the battery power connection at the false bulkhead in the engine bay, the high power protection module, the battery terminals and the negative battery cable-to-body ground.

If you don't have a copy of the X308 Electrical Guide, send me your email address via private message and I'll send it to you in pdf form. The link for downloading the manual from this forum is currently down.

Cheers,

Don

 

Paj, follow the Electrical link in my signature, it may help you out.

 

Rob,

I've passed along the link to your excellent troubleshooting guide to others before and should have thought to mention it to PAJ. On behalf of all of us, thanks for all the time, effort and expertise you invested in this excellent diagnostic resource!

Cheers,

Don

 

Thanks for the kind words, Don. I enjoy being able to help out, and making that presentation saves me a lot typing every time a member asks for advice.
So really, it comes down to being too lazy to type......