Have a not-charging issue on my 89... New Battery and worked fine until I stored things over the winter and had a few battery charger instances to get things back on track for the spring. However, I notice now I'm not getting a charge any longer. I can get around for a while, but the entire time the dash is reading low and eventually the battery will die and the car will too..


Does anyone have any info on how to take the Load Dump Module out of the troubleshooting equation? Is there a way to bypass it, or test it directly, to see if it's involved?


Thanks,
Pete

 

I used to just remove the grounding wire (module-to-body) and if the alt charges, then the module is faulty.

bob gauff

 

Had the same issue last summer. Remove the LDM ground wire from the lug as Bob suggested.

 

The connection you're referencing - is this the connection that goes directly to the alternator?

Got the tip a bit late and already had a new alternator in hand and a oil sender replacement I needed to knock out, so I replaced the alternator while I had it out... was hoping to knock things out at once, but the Jag has other ideas. The new alternator is in and same condition - not charging... so I may be doing this load dump module check (hope it's not that, it's a lot easier finding alternators than it is that custom module that goes to a special blue jag connector, and one other I believe...

Pete

 

Pete,

Responding from my phone, so this will b short. From the LDM casing, follow the black lead back to the grounding lug, near the drivers front headlamp assembly. You may need to remove the air cleaner assembly, i don't recall at this moment. Be sure to disconnect the battery while doing this, giving the memory an opportunity to reset when you fire it up.

 

Forgot one thing, one of the leads from the LDM goes to the center fuse box under the armrest,(i doubt its the problem), from the center fuse (dont which one specifically) the circuit travels to the dash providing the charge indicators

 

Thanks Rob - did the test (didn't have to remove the airbox, as it was just a 10mm bolt holding a bunch of grounds to the chassis). Once I started the car up with that grounding wire removed, the charging issue went away...


Now the new question is... ... what does that tell me exactly? I have a load dump module DBC4267...I can probably take it off and open it up to see if there's a replaceable circuit board component that may be gone...


Thinking back, the only thing out of the ordinary was charging up the car from sitting idle most of the winter. I wonder if the charger blew this module up. Now I have new variable in the mix, with a new alternator as well...


Pete

 

I don't remember if the load dump is a 'one-time' use type or just 'bleeds-off' excess.
If it is like the 1988/89 ABS overvolt module then it is a 'crowbar' type safety (meaning it blows a fuse by means of a zener diode).

If the module has failed you can pry it open to investigate. Your charger might well have damaged the module????

bob gauff

 

Good question - I'm not quite sure how to test yet... Here's what is inside the mysterious box though. Nothing looks obviously wrong though...

 

I actually picked up the correct numbers on the zener diodes... ZP5028S 8846 was on both of them. I think there were some threads on another site that mentioned replacing the diodes and having success, I won't mention the site but it's the jag site that's like going through an 15 year old website time machine. Does anyone recall ever seeing specs on what to parts were used in the repair specifically? I have a couple ideas, but I don't want to post them as I'm taking a wild stab at a replacement and don't really want to put anyone else's car in risk.


I also ran across posts mentioned just disconnecting that ground wire and it could do no harm...but I don't fully understand how that works technically, thus the reason why I would like to replace a couple cheap components and get the part back on track. Since I may have blown up this device with my charger, odds are it may have done what it was intended to do and save me some other things going bad.


Appreciate any info anyone might be able to throw into the mix!
Pete

 

Pete,

No problem mentioning Jag-Lovers. Plenty of us are members there also, and they still have a huge archives of XJ40 info, including most of my own phototutorials.

I wish I could help you on the dump module repair, but it sounds like you're on the right track. Hopefully someone who's done the repair will chime in.

Cheers,

Don

 

Still on the hunt for a suitable diode... I'm not real clear on the suitable replacements..there's a lot of specs that go along with these, but I'm not real clear on which ones to hone in on yet, to make sure the replacement is going to cover the necessary specs...