I have a 2001 XJR that is having a weird electrical problem.

Power Fade Issue:
Sometimes when it is idling, or sitting in traffic, the electrical system will momentarily have power fade. For a brief second, all lights dim, dash lights come on/off, sometimes it says Traction not available, and my radar detector loses power, and then everything pops back on to normal. The HVAC blower fan slows down, but never seems to completely lose power.

It is not a clean off/on; rather it sort of fades out and seems to ride the threshold of losing power and not; I can tell because the radar detector acts like someone just barely unplugging and replugging the power plug.

It usually happens in hot weather (90+ deg F). It happened last summer, but not at all during the winter, and now again this summer.

No-Start Electrical Weirdness (related?):
Now it is doing something a bit more scary. After nearly every trip, I'll turn the car off, take the key out, and then it starts doing all sorts of weird electrical things. The odometer fades, and blanks out, things click and make noises behind the dash (relays?), and wipers and other things start stuttering and moving slightly; accessories start beeping and making noises. Like everything is losing & gaining power intermittently. This includes the automatic retracting seat and steering wheel. If I put the key back in, and try to start it, I get nothing, except all the beeping and whirring of accessories going crazy. If I repeat the cycle of taking the key out, putting it back in, and trying to start it a few times, eventually things go back to normal.

What I've done so far:

1. Replaced battery
2. Replaced Alternator (Bosch)
3. Replaced the main braided ground strap with a brand new battery cable from AutoZone. It's the type with insulation along it's length.
4. Tightened all positive connections in the trunk, and on the front right of the engine compartment.

Thoughts:

• I'm thinking perhaps a relay, or a computer, or a circuit board? Maybe something is getting hot, and causing the issue. Then when things cool down, they function again. This would make me think of something under the hood. I do hear clicking and such from under the hood when the dash starts going crazy.
• Maybe something in the ignition control circuit; between the key and the computer?

I'm hoping someone has some experience with a similar issue, and can guide me in the right direction!

Thanks.

 

That is a weird one! Follow the electrical link in my signature. You've already done many of the steps, but use a meter to make measurements.
As for the power fade, does it happen with the AC turned off? I ask because on my car, when the AC cooling fans kick in, the voltage drops about 1 volt, and that's on a pretty healthy car. They obviously pull a lot of power.

Combine that with a bad connection somewhere, and you have your power fade.

 

it's probably been covered but there's an engine earth under the car that grounds between chassis and engine just forward of the trans bellhousing, get a look at it's condition/connections and clean/grease them.

Tightening those bulkhead connectors isn't enough - removing them altogether and replace nuts and washers with stainless, dielectric grease and cleaned up terminals/connectors. The little short one between the fuse boxes connections are the ones that sometimes oxidize badly on the underside.

Being in the UK this crap is fairly common (wet/humid/salty). I've just seen this behavior cured on a 98' XJ8 after the above treatment to the main power cable ends, the short one caused it!

hope that helps

 

Sean, thanks for clarifying that tightening isn't enough. Would you please tell me specifically where the short fuse box cables that you mentioned are? Trunk/Boot? Engine compartment?

In fact, if you can list all the connections you think I need to clean, that would be so helpful. I felt like I touched all the connections, but that obviously isn't true since I missed the fuse box cables.

A quick reply would be appreciated since taking it to my mechanic friend tomorrow to get the connections cleaned, and I want to make sure we get all the connections.

And avt007, yes the fade does mainly happen when the A/C is on, and yeah, it probably is when the fans kick on. Good call. And I agree that a bad connection is likely the cause of the power fade. Now that Sean mentioned the fuse box wires, perhaps that's all it is. Gosh, I hope so!

Thanks Again!

 

As Sean B has pointed out....it seems to be the only thing you have neglected to do so far is to check and look after the earth return system ;o)
Perhaps this will help explain the major connectors in the X308 system:

POWER CONNECTIONS Photo Gallery by Max Heazlewood at pbase.com

Work your way through this system and take resistance readings as you go.
As for voltages, you should have at least 12.6 at battery and 13.8 to 14.2 with engine running and lights on high.

This will be a start....nonme of these connections like corosion and it's always the exposed connections that cop it. ;o]

 

as above
power-005......... with stronger 50 amp relays photo - Max Heazlewood photos at pbase.com
This picture and the black caps with the red marks are the ones to check first, it's the short cable between the fuseboxes, I'll bet the issue lies there.

 

Ok, I disassembled and cleaned all positives and ground points shown in that Max Heazlewood phase gallery. I also found one more ground point on the dead center of the firewall under the bracket assembly that holds a bunch of things (I'll post a photo later).

So, I THOUGHT everything was ok now. I was going to write a SUCCESS post, but I thought I'd wait a few days. Sure enough, tonight it did it again. Went nearly dead, and wouldn't turn over. Dash was very dimly lit, and making faint funny noises even with the key out.

I had no tools, but I fiddled with all the underhood connections I could reach. They were all tight, and nothing made a difference. I physically removed each of the brown relays in the fuse boxes on the front left fender. I removed them one by one, and then checked the dash. Nothing made a difference; the dash was still doing faint weird things.

I got mall security to give me a jump start, but since I couldn't get in the electrically operated trunk to get at the battery (brilliant design..ugh), I had to jump it with the positive lead on the false bulkhead near the front right fender, and the negative lead on a bolt for the upper shock mount assembly. The first time they tried jumping it with a jumper pack that I think was worn down since they had just used it on another jump start. The car did wake up, and act normal, but when I turned the key, it didn't start for lack of juice. Here's the weird part...when the jumper pack was turned back off, the car was still malfunctioning even though it had been working just fine with the jumper pack. So, it seems all of the under hood connections must be ok. It's just not getting power from the battery somehow.

Anyway, we then just jumped it directly from their running vehicle. It worked. The car woke up, acted normal and started right up. Then, I decided to turn it off as a test while I still had them there. It turned off, acted normal, and then started right back up. Why didn't it do that after the jumper pack woke it up. It's almost like the car had to actually start in order to get everything working properly again.

So, I'm wondering where else to try connections. I did everything I could find under the hood (everything in those Max Heazlewood pictures). In the trunk, we cleaned the battery terminals, tightened (but didn't disassemble) the 4 lug power distribution box, the trunk fuse box power cable, and all the grounding points for the battery, etc.

But somehow it's still losing power from the battery. The battery is only about a year old, and is a Bosch unit, but it has developed some leaky stuff at the top that has corroded the metal strap that holds down the battery. But when running, the car works just fine, so I'm thinking it may not be that.

In avt007's "Electrical Troubleshooting" link, it mentions two "Heelboard" fuse boxes that are between the 4 lug power distribution panel and the front left fender fuse boxes. Where are those? Under the rear seat? How do I get the seat out? I tried lifting up on it, but it wouldn't come up.

Also, since I connected power at that false bulkhead, and the car woke up, it seems that that might also have gotten power to those fuse boxes, but avt007's diagram shows that that is fed from the power distribution panel, which means they would have passed through those heel board fuse boxes, so those may not be the culprits.

I wonder if my newish Bosch battery has failed?

Or it almost seems like a relay or switch that is not closing. What relay or switch should I check? avt007's document mentions the interia switch....what is that...the thing that trips in case of collision? Seems unlikely. Could there be some other main power or dashboard relay that is not closing properly?

Help please!

 

Or, is there a main power fuse that could be just barely broken? That is exactly what happened to a Honda owner here: Intermittent loss of battery power - Car Talk

Where are all the fuses that would affect overall power delivery? Aren't there some in that 4 lug power distribution box in the trunk?

 

Oh, look at that, my trunk keyed latch rod mechanism was just jammed after 13 years of never being used. My key would only turn 1/4 turn with VERY hard force, but do nothing, and since the only time I ever tried it was when the car had no power, I just assumed it was an electric switch, not an actual mechanical joint that was just jammed. I peeked behind my trunk liner, and gave it generous squirts of WD-40, and then worked it in a lot with the key, and now I have mechanical access to my trunk. Yay!

Now, I just need to figure out why it loses power.

My Bosch battery was new as of July 2013, and it says "36 month free replacement," so I think I'm going to give that a try simply because of all the leaks and corrosion on the top of the battery. Here's a photo of the battery that I took tonight:


And I checked those big fuses in the 4-lug dist. panel, and everything looks ok from what I can see. Not sure what's behind the fuse's plastic panel in the middle where they say "MEGA."


One interesting point is that my car has a 500A fuse, and a 175A fuse instead of the pair of 250A fuses as shown in Max H's photo. My box and connections are also rotated 90 degrees vs. Max's car. Variations in the vehicle years or options, I assume.

Anyway, I still welcome any ideas about other joints that need inspection, or relays, etc.

 

I mentioned in a post above that I found an extra grounding lug/point on the firewall under the wiper motor, etc. Here I show it circled in red. (Apologies for the overexposure...there was a too-bright flashlight being pointed at it).

 

Battery - this looks like its game over.

 

The heelboards are where the rear passengers heels would be. Use a coin to turn the plastic button and pull the panel off on each side.

I'd measure the power fuses in the trunk again with a meter.

 

►Are you suggesting measuring voltage while running or not running?

------

I'm getting the Bosch battery replaced ASAP either today or tomorrow under warranty. Not sure if that's it, but I sure hope it is.

I may try to get at those heelboard connections tomorrow, too, just to check them.

Are there any fuses, relays, or switches that might be having trouble, or getting stuck, yet get reset when the jumper car's battery is connected? If this new battery doesn't work, I can only imagine it must be a relay, etc.

The weird thing is that until last night, the car has been acting completely normal for 4 days since cleaning all the connections. And it's acting completely normal today. But last night, it certainly had that epileptic seizure until I jumped it.

Thanks for all the help, everyone.

 

I'd measure it while running, and I'd wiggle the cables too. The cutoff switch isn't hard t get at, maybe press that and see if it helps.

 

Fast Cat, your problem inspired me to dig deeper into my car, and why the headlights dim when the fans kick in.

What I found was, the cable between the battery and the High Power Module was bad.
With the key on, and engine not running, there was a 0.7 volt loss between the positive battery post and the big fuses.

Closer investigation using a volt meter proved the loss was in the crimp where the cable was joined to the battery post clamp. Flexing the cable made the loss change, which could account for your intermittent issue.

Another clue was that the cable was hot to the touch, something that shouldn't happen.

The cable looked brand new, but appearances don't prove anything.
I removed the cable and soldered both ends on. The loss is now 0.01 volts. I went through all the cables, measuring for voltage loss, and feeling for heat.

No other issues were found, and now the dimming is gone, and I have 14.0 volts at the engine bay fuse box.

 

I thought you replaced the braided ground strap at the battery ? (it's in the photo above) Mine failed where the braid meets the battery end, like avt007 said, but mine was the ground strap. I found out when I was attempting to jump start the car and the ground strap was burning hot. I replaced it and the other braided cable (engine or bell housing to frame) with old heavy insulated cable.

 

I can only draw from the OP Jim and Rob's experiences here, but hot cables and a battery that's obviously suffering means that both +/- battery cables may fix this and improve once upgraded. HiFi size 0 and solder...I wonder if this would be better than loose galvanized stuff the factory fitted, particularly underneath.
0 Gauge Wire 1 0 40 ft 20 Red 20 Black AWG Cable Power Ground Stranded Amp | eBay
Bosch are made by Varta, they don't go wrong after a few months, if ever.

I really hope this sorts out the problem

 

I'm finally getting around to updating this thread. After replacing the main ground strap, and cleaning pretty much ALL the main power connections listed by you very helpful people, I was still having the issue, but I finally found the issue, and have had no trouble in the months since fixing it.

The root cause was that the battery had suffered mechanical damage due to the tie-down bar. This damage lead to that flaky intermittent behavior.

This is what the OLD troublesome battery looked like in the car. Obviously, there's acid leakage, but take special note of the metal bar that holds the battery down. The bar is a U-shaped bar that, in this picture is installed per the factory fit with the rounded part of the U cross section touching the battery top (you're looking at the inside of the U). Ultimately, THAT was the cause of the problem.




So, after taking the battery tie down bar off of that battery, I found that the vent tubes that stand proud from the top of the battery had gotten crushed down into the battery by the tie down bar. Note the concave "craters" around the vent tubes.






So, after replacing the battery (for free thanks to Bosch's great full replacement warranty), I decided to install the tie down bar upside down so that the inside of the U cross section would make clearance for the vent tubes. The only problem was that the tie down bar has a bend in it from the factory, and the threaded posts in the car were not long enough. So, I had to use a small sledgehammer on a concrete floor to bang out the bend in the bar. Then I installed it upside down, and it clears the vent tubes perfectly. No issues for several months now.

This is a view from inside the trunk of the main vent tube that sits toward the front of the car (the daylight you see is looking out the trunk from the inside). You can see the tie down now makes clearance for the vent tube.

 

Thanks for posting the final fix. Good job.