This is on a 1996 Vdp 4 litre. Recently I noticed that on startup and at low idle the charge gauge reads low-below 10. Once the car gets going on the road the volt reading is 14 to 15 - it seems a bit high if anything. When I slow down or park, the reading again drops below 10. The battery seems ok, although the engine does seem to turn over a bit slowly. It always starts though.
Do the voltage readings and fluctuations sound normal? If not, what can I expect to fail or require replacement? I do want to deal with this before the Jag leaves me stranded.
Thanks for any help.

 

A fully charged battery is 12.75 volts at the battery terminals

Once a load ( during ) is required by the car the reading up forward ( not at the battery ) can be less because of connections limiting the current flow ( this is a dynamic functional reading )

There has been history of these connections becoming loose

After a long starter duty the battery voltage will be somewhat below the 12.75 at the battery

After the engine start you should see the alternator regulated voltage very quickly of 13.5 to 14.5

At a stop sign you should be stable during this time period as you're not charging the battery

Your voltage regulator is not stable even with RPM changes and appears to totally fail at lower RPMs hence you are seeing battery voltage at lower RPMs

The voltage regulator is inside the alternator assembly and can be changed yourself

Part # IN435 is the generic #

Alternator Red light on the instrument cluster ?

You can place some masking tape on the gauge and mark a hash so you can quickly glance at it instead of the time to get your division marks determined

Once you take the car to a shop and they measure the voltage at the large B + terminal on the alternator you are at a alternator change

Lately there have been a decrease in the price of a replacement but have not been reliable

The original is a Denso 130 amp

I had no luck ordering this VR from E - bay vendors as they would send me the wrong one

But this brick and mortor store has more skin in the game to be correct

# IN435 Voltage Regulator for Denso Alternators, 12 Volt,On: Asuna (1993-1993) , Geo (1990-1993) , Isuzu (1990-1993) , Jaguar (1993-1997) , Jaguar - Europe (1994-1997) (alternatorparts.com)

The jaguar wiring only has 2 wires in the 3 wire round connector

 

Parker, Thanks for your reply. No warning lights are on. I do think the gauge is good as it does react consistently to increased and decreased rpms.
Instead of spending a lot of time testing things, I'm tempted to just install a replacement voltage regulator. It's not that expensive. Can it be replaced without removing the alternator, or what is involved? Does that seem like a reasonable thing to do, or am I likely wasting my time and money?

 

The alternator should be removed but you can explore he possibility of not needing to remove the alternator

The cover on the aft side has to be removed to get to the VR

The 3 nuts on the aft side in the pic below must be removed to remove just the cover so there is the possibility

There is one screw that can be fused and stuck and needs the head drilled off

this will be point Ps




This may require you to replace the brush assembly if the case or wear amount

Brush Holder Assembly for Denso Series Alternators (alternatorparts.com)

The alternator comes out from the top but there is the long pivot bolt to remove from the bottom

on this long bolt there is a bushing that stays in place on the engine side bracket

The alternator may be pinched by the bracket and can be levered out with a long screwdriver

There are 2 small wires attached to the alternator other then to 2 wires in the round connector

You should mark these wires before removal

The auto parts store has a spin up machine that will test the voltage regulator before you reinstall the alternator

Editing

 

A test you can do in how your car is responding is mark the voltage gauge before starting the car and after starting and not throttling up to get the voltage regulator to come alive turn on the blower fans for awhile to continue to drain the battery

after a while shut the engine down and observe the voltage gauge in your case my not have charged to recover

You will probably need to jumper the car battery to be able to start again the next time needed

There is a fuse involved for the VR but in your observations it does eventually come alive so the fuse is out of the question

You can swap this relay with the one on the left for in reality the left is only the horn

This fuse is # 10 / 5 amp right engine fuse box and this fuse requires the right engine fuse King relay to close

Notice how this generator / VR wire goes through the Papa Indy 61 pin 2 connector which has a history of going bad

Click 2 times on the image to magnify

 

Could your drive belt be slack?

 

 

I won't try to take anything apart until the new VR arrives; that could take a few weeks or longer as it is coming from the other side of globe. The alternative was to buy it from the local auto parts store, but they wanted upwards of $600 just for the VR.
Can you tell me whether the brush assembly 3982033 is the correct one for the '96 4 litre? Or is there another number? I might try and pick that up as well before disassembly.
I also will check the belt tension.
Thanks for the help. While I have mechanical experience with various makes, my knowledge of Jaguars is quite limited.

 

Simeone found the screw joining the VR to the brush assembly was not stuck but mine was

I'll have to look in the garage on the brush invoice or look at the old one as they are a identical picture match

Replacing the belt can be critical on the length of the belt even though it is adjustable from reading others experiences , I have the length of a original Jaguar stamped belt

The engine has a history of the harmonic balancer letting loose and not driving the alternator so would be a check as you are in the area of concern

Mark the pulleys with a paint stripe and after engine run high electrical load and engine shut down they should still be in alignment

The A/ C compressor should also be run as the separate belt but same HB

The pic is from Aholbro1

 

I think you would have to be Houdini to replace the regulator with the alternator still attached to the engine!

 

Well, I ordered a new voltage regulator on Amazon back in November. It never arrived. So, back to the drawing board.
I do have a 2000 or 2001 XJ8 parts car that has an alternator on it. Can anyone tell me whether the XJ8 alternator will bolt onto the 1996 XJ6 VDP? If not, can anyone point me to a concise explanation of how to install a GM alternator on the XJ6? Thanks for any help with this.

 

 

I just had my X300 alternator front bearing replaced by a alternator shop and I asked them where they get their VR's from

How you would order and the part # is a question

Regitar USA, Inc.