Hello, All! This is my first post on the forum. Thanks in advance for any help.

I bought a 2001 XJ8 about 6 weeks ago. The problem started a few days after purchase. A transmission error came up, so I went to the dealer for a diagnostic. It turned out to be no problem, but they had to jump the car to start it. I wondered if there was a slow draw on the battery, or a damaged battery, so I let the car sit for a few days. It started up just fine, and I've been driving it almost every day since then with no issues.

A few days ago, I made several trips about town (each lasting 5 to 15 minutes). Each time I started the car, it seemed to be a weaker and weaker start. I drove to Advance Auto for a test. It showed that the battery needed charging, but was good. He suspected the alternator was bad due to the voltage drop when I turned on the lights and AC. I drove home, and as I pulled into the garage, the headlights came on automatically. This caused the revs to drop and warnings "Trac Control" and "ABS", etc. to show up. I turned off the car and tried to restart. Nothing. A few clicks, a whir, and no cranking.

I jumped the car and it started after a bit of a strain. I tested volts after removing the ground cable (the car continued to run, so alternator didn't jump out at me). They read fine. I put the ground cable back on and turned on the lights and AC. The same warnings came on. I removed the ground and the car stalled.

I trickle charged the battery, and it started just fine. I removed the ground cable and read voltage, which was good (alternator is pumping voltage). Without a lot of electrical load (no radio, AC, or lights) the car will run for about 5 minutes. Then it seems like a relay trips, the voltage drops, and the car dies. If I try to start it right away, I get nothing. If I wait a while (5 to 10 minutes) it will start up as long as the battery still has enough juice. Another possible symptom is that when I rev the engine, the engine drops revs for a slight pause before revving up. I checked the terminals/fuses in the trunk behind the spare tire and at the passenger bulkhead for corrosion and/or melting. They're good. I switched up relays all over the place. No effect.

I don't think the battery is bad. I don't think the alternator is bad. I think there might be a short that is causing a voltage drop leading to a battery drain during short trips, or affecting the alternator somehow. Will a short affect a relay? How do I diagnose?

Help!

 

You seem to be doing all the right steps in trouble shooting the problem but did not post the battery voltage under various conditions. The voltage should be 12.6 fully charged, 14+ with the engine running, even with lights and everything else on.

Sounds like an alternator to me.

 

Check the bulkhead fitting on the cool box underhood on the passenger side. Theyre known for getting high resistance and causing all the issues youre experiancing

 

The voltages were good. It would strain a bit under lights and AC, but then recover.

The alternator still jumps out at me, but I've never known one to work sporadically. Usually, they're working, then they're dead. The car will run for several minutes with the alternator putting out good voltage, then low voltage warning-click-stalled. Without the AC or lights on.

I looked at the bulkhead connections, and they looked good. Do you think I could still have a problem if they looked clean and tight?

 

Never run a car with the battery disconnected, it is almost certain to damage the alternator. A healthy car will run the voltages posted above. I'd recommend getting the alternator tested by a shop. Once you know you have a good battery and alternator, then you can start proper troubleshooting.

 

I haven't run the car with the entire battery disconnected, just the grounding cable disconnected per the JTIS inspection process. All the voltages are good until about 5 minutes into the run. Then voltage drop-click-stall. I'm thinking some kind of short somewhere that drains all voltage. Could there be one in the alternator itself?

I'm sure replacing/deep charging the battery would give me a good run of driving, but the problem would repeat after the battery slowly drew down due to voltage drops.

I guess my next step is to start with the alternator removal process to at least get a closer look at it. If no obvious short or loose connection is visible, I'll get the alternator into a shop for a test. Could a short somewhere else in the system cause damage to the alternator?

 

This opinion. It is hard to tell by just looking at it. But my 1st XJ8 had a short in this area that would drain the battery.

 

Before removing the alternator, I'm going to try to bypass the bulkhead terminal. If everything works well, I should know that I located the problem area. Right?

 

If the bulkhead fitting is the problem, does it require replacement, cleaning, or what? If replacement, does anyone know a part number/description I can use?

 

if its clean and tight, probobly no tthe issue. I would go to the ground strap. Matter of fact it is easily replaced with 2 bolts under the car from frame to body. It is down under the car getting water and grime on it constantly. We do replace a few a yr in texas. More north, more often. And alternator doesnt need to be taken off to test. You only need a dvom to check voltages. In idle,test at the back of the +stud on the alt. Take the air box out but leave the mafs hooked up to allow room. . Check output without anything on, then switch on ac, blower set to high. All lights on etc.. And watch for what the alternator does. It should have no issue keeping up with only a momentary drop bewtween consumption and recovery. If ok go to the + post and measure the voltage. The differance netween the battery and the back ogf the alt should never be more than .2volts or you dont have a low resitance connection between the 2.

 

Thank you all. I'll get cracking and let you know what happens.

 

Update #1:
Removed and cleaned up the bulkhead fitting. It was clean already, but I did a good spit and polish. Tightened it up and started the car. Removed the ground cable and attached the multimeter. It ran at about 13 volts for about 5 to 10 minutes, then a relay clicked and it stalled. I was looking at the meter and did not see any voltage drop, just BAM -- click-stall.

I'm going after the alternator next. . .

On another note, what's a safe and easy way to remove the brown covers from the relays? I would like to do an internal inspection on them.

 

Toothpicks and a small screwdriver.

Have a local auto parts store test the ENTIRE electrical system . . . free!

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

DO NOT RUN THE CAR WITH A MAJOR GROUND DISCONNECTED ! ! ! !

 

You're freaking me out, test point! I don't want to hurt my baby, so I've been following the JTIS as best as possible.

This is from the JTIS 414-02. You know it's legit because it uses the word "whilst" :

Testing the Battery Circuit Using the Vehicle Battery
Remove the battery cover.Ensure that all electrical loads are switched OFF and that the engine is cool.Start the engine and allow to IDLE.Whilst the engine is idling, disconnect the battery negative terminal and, using a digital multimeter (DMM), measure the voltage between the terminal on the battery negative cable and the battery positive terminal. If the generator is working, the measured voltage should be within the range 13V to 15V.This indicates the system voltage without the battery in circuit. If the generator is inoperative, the engine will stall when the ground lead is disconnected.Repeat the test, using the ground bolt, as indicated (shown dotted on the illustration). There should be hardly any detectable difference in the voltage reading (due to minimal current flow); if there is a detectable difference, clean the cable terminal and the adjacent area of the body.

 

Regardless of the source, running the alternator without the battery in circuit is dangerous to the health of the system. More than one experienced person has told you this in this thread alone. The person writing the jtis section may not have ever touched a wrench in their life, and may have copied his text from the internet for all you know. Such is the power of low bid procurement.

The same measurement can be made *without* disconnecting the battery and it will be in the same range for a healthy alternator.

Forget the relays and anything else until you establish beyond doubt that the alternator, battery, power distribution and grounds are good. Otherwise, you will just be flailing about. Thus far, they are still suspect.

 

I'm going to withhold the condemnation for running without battery ground connected, at least until one of the Jag techs chimes in here... although it is very common to preach NOT running the engine on a modern, computer controlled car with the ground disconnected - lack of a stable voltage, not exceeding 14.5 Volts has been known (or at least has been alluded) to have blown the delicate ECM and other electronics on lesser cars than the Jag.

However, since it is a troubleshooting technique specifically spelled out in JTIS, I'm going to assume, for the moment, that in this case it may not be an invitation to catastrophe as implied with other vehicles.

That said, since your test shows that the alternator IS working, at least for 4 or 5 minutes, and then appears to stop generating supply voltage, I'd suggest another (much safer) test.

Just reconnect the battery and do the same test again. You should see around 13.5 to 14.5 VDC at the battery when the engine is running... and after five minutes, if the voltage starts to drop again, then I suggest the alternator is indeed failing. It may take more than 5 minutes this time, since the battery is picking up a significant portion of the transient loads. I'd also suggest turning every thing you can on - A/C full, lights on, etc. to load the alt as much as you can and keep checking voltage both at the battery and at the front feed-through stud that you cleaned. See where and if any voltage drops occur, and whether the charging voltage is maintained or drops off after a few minutes...

 

I agree with QuadManiac on all of that. The procedure for floating the system off the battery has been used for years by mechanics a all ilks and will probly NOT do any damage, but for a system with a compromised voltage regulator, it could certainly lead to high voltage on all of the modules with potentially disasterous results. And his defined test method will give the most accurate diagnois, in that you do not know if the load switching in is just a transient high current peak, or if it is truly adding a load greater than the alternator;s capacity.

And just for info from the world of electrical engineering... an electical device with one wire connected is equivalent to not being connected at all.

 

I'm sold on not running it without the ground attached. Better safe than sorry. I know what you're saying about the guy writing the manual not knowing his stuff.

None of my tests require this type of test anymore, and I'll keep it in my memory banks for future (god forbid!) problems.

Indications are funneling toward the alternator, so I'll begin formal tests on that soon.

 

You should take the car in to someone who can do a proper load test on the alternator. I have had alternators fail in the same manner you are describing. All outward signs are that they are working but actually with any load they are not producing enough and the battery begins to discharge - as the voltage drops the car begins to shut down and finally the engine stalls. The heat also has some effect -- maybe it is the electronics in the regulator not working correctly when hot .... Many Mercedes Benz's are famous for the regulator pac going in the alternator ...especially when hot.

When you get a low voltage situation in an XJ all kinds of strange things can happen. The warning lights and strange electrical problems should be fine once you get the charging system sorted out.

 

I finally got the alternator out and tested by an alternator specialty shop. It tests fine. UGH!

They suspect it may be a wiring issue causing a bad ground, or not allowing the regulator to talk to the alternator. Either way, I'm back to (almost) square one. This is one of those rare cases where you prefer to hear "it's broke" instead of "it works."