Hi Folks,
I have a 1993 Jaguar Sovereign in very nice condition, so I don't want to scrap it. It has a weird issue with the starter. When I am driving along and go over a bump the starter motor engages for a split second, all the dash lights and headlights go dead (seems to be a dead short not just voltage drop) and then it returns to normal. Of course this makes the same gut wrenching sound as trying to start a car when the engine is already running. I have taken it to a reputable Jaguar workshop in Adelaide, South Australia and they cannot find the problem. They really don't want to work on it because it's a 1993 vehicle and they keep telling me that it's an old car etc etc etc. Obviously (and I don't blame them) they prefer new Jags that they can change the oil and charge Dr Smith $2,000. Unfortunately I am not Dr Smith with thousands of dollars to spend.
Does anybody have any ideas? I am a qualified retired electrician, but not an auto-electrician, but can't figure this one out, it's weird!
Cheers, Bob Marshall

 

Could it be the relay for the starter, contacts momentarily closing? A short on the solenoid wire on top of the starter? Just two things that come to mind.

 

Hi Robman25,
Thanks for that suggestion. Starter (and solenoid) have been out and Jag guys put a complete new unit in to see if it would cure the problem. No change, it still did it. I asked them to put the original back.
There is a "Starter Module" behind/near the glove box that seems to be sealed and apparently contains four relays. I may try fitting another unit there just in case. I will try to chase down another one from a wrecker. Beats me how they need four relays to operate one starter motor!
This is so frustrating as it has already cost me $1,000 in labour with no result. I was hoping someone would have had this issue before and knew the right fix.
Cheers, Bob M

 

Hi Bob,

Welcome to the Jaguar Forums! It's great to have you with us.

I like Robman25's suggestion of a problem with the starter relay, which is just one of the four relays in the blue module behind the glove box. A known problem is cold, cracked or starved solder joints on the circuit boards inside these relay modules (and most other components in these cars!). You can carefully remove the cover, slide out the circuit board with its relays, and inspect all the solder joints for solder joints that are obviously cracked, dull instead of shiny, or lacking sufficient solder for a secure connection.

The wiring terminals on the starter are exposed, so it could be possible that they are shorting together somehow, but presumably this would have been resolved when the new starter was installed.

There are other potential suspects in the starter circuit, including the ignition switch itself, and the Central Microprocessor (CPU). The ignition switches are known to fail, and are easy to replace (the electrical switch itself, which clips to the end of the key barrel).

A known problem with with the CPU is water ingress due to clogged drains under the A/C evaporator that run alongside the center transmission tunnel. When the drains become clogged with deteriorated foam rubber insulation from the HVAC system, water pools under the evaporator and sloshes onto the CPU when making left hand turns. You can check the CPU electrical connectors for corrosion and for signs it may have been wet.

As a retired electrician, I think you will be able to make sense of the schematics, which you can download at the link below. Note that the page before each schematic lists all the components and gives their locations, which can be very helpful:

Jaguar XJ40 Electrical Guide 1993

Another resource that can be helpful is the Haynes Repair Manual, which you can download at the link below. It's a U.K. edition that is missing a couple of chapters, but it has diagrams that show the relay locations for the various model years:

Haynes Jaguar XJ40 Repair Manual

Also, I have photos of the CPU location and the ignition switch replacement at the link in my signature - unfortunately the large images are not currently working at the Jag-Lovers forum but maybe the thumbnails and descriptions will help.

When you get a chance, please visit the New Member Area - Intro a MUST, and post a required introduction so we can learn something about you and your Jaguar and give you a proper welcome.

Cheers,

Don

 

Hi Don,
Thanks for your suggestions. This is the sort of advice I was hoping for. You obviously have experience with these cars.
I have no doubt the problem is something simple and once found it can hopefully be a simple repair. I have had visions of having to scrap this beautiful car over a minor part failure. That would be an absolute shame.
Yes, I think Robman25 is probably on the right track as well.
As far as I am aware the earlier XJ40s had numerous electronic problems. Many faults were apparently resolved by the 1993 model which mine is. At least I now have a starting point and I have access to a couple of reputable wrecking yards for reasonably priced second hand spares.
Thanks again and I'll keep my fingers crossed and look further.
Cheers, Bob M