Hi,

I have a 1992 xjs 4.0 with 63k on the clock.

For some time now on occasions the voltmeter shows 11v and then after driving a few minutes it shoots to 13v.

Recently it has dipped into the red 9v and the car has died. When I fully charge the battery the voltmeter shows 11v with the engine off. When driving it no longer shoots to 13v.

Can anyone please advise on what the issue may be please?

All the best,

Zarathushtra.

 

Zarathustra,

First of all, don't trust the voltage readings of the gauge. They are notoriously inaccurate suffering from poor connectivity and earthing issues in the instrument cluster. The only thing you can rely on is if the gauge shows above 13v, the alternator is almost definitely charging the battery.

So start by measuring the voltage at the battery terminals and then at bulkhead terminals with ignition off, Assuming that the readings are above 12v and within .1 - .2v of each other, then turn on the ignition and repeat. Now start the engine and measure at the bulkhead terminals. If voltage doesn't move to about 13.7v + blip the throttle to 1000rpm+.and see if it improves.

If you're getting massive dips in the voltage when driving, I suspect it's an intermittent regulator failure. See if you can run some extension wires from the bulkhead terminals to a voltmeter inside the car to monitor. The regulator can be rebuilt quite easily and cheaply. I had mine done a few years ago.

Good luck

Paul

 

Thanks Paul,

The voltage reading is not raising above 11v.

I'm a bit of an amateur. Can you please elaborate on 'bulk head terminals' ie where they are?

All the best,

Zarathushtra.

 

Problem solved very easily. I removed the battery over the weekend, logic being all electrical components could reset, replaced battery and all is fine. Hope it lasts.

Thanks everyone for your help,

Zarathushtra.

 

Zarathustra,

Apols, I didn't have access to my car until yesterday.

On late facelifts, there are 3 bulkhead terminals. On my RHD UK car, there are 2 negative terminals on the right hand side of the bulkhead, just inboard of my brake Actuation Unit mounting. On the left hand side of the bulkhead there is 1 positive terminal just inboard of the scuttle drain tube. All of the terminals are normally covered with rubber boots. See the pics below with the boots loosened off.

I'm glad to hear you've sorted the problem with a new battery. However, I really suggest that you test the voltage at the battery (or bulkhead terminals when the engine is running to confirm that you haven't fried the regulator unit in the alternator. You should have 14.1+ volts with the engine running.

Cheers

Paul

 

Thanks Paul. I'll monitor and check.

I didn't replace the battery only disconnected over the weekend.

All the best,

Zarathushtra.