XJS Speedo

[XjRestorations]

Good morning all,

Help needed!
We have a 1993 4.0ltr Facelift XJS on site, which has had bulkhead welding repairs carried out.
The entire dashboard has been out to repair - now it is back together, the speedo refuses to register speed.

The interface unit has been swapped for a known working unit (taken from a running, testable car), as has the transducer - the two first weak links in the system. Makes no difference.
We have borrowed a 6.0ltr Instrument Pack, does not work in the 4.0ltr. Carried out the swap in reverse, and the 4.0ltr IP works in the 6.0ltr - so not an IP issue.
The blue wire from the interface unit feeds the EMS, Cruise (not fitted on this car) and the speedo via a three way split. Continuity through the blue wire which becomes a yellow white at pin 10 on the IP feeding the speedo. So no break or pinch in the wire (a possibility with the dash removal having taken place). To be extra certain - a direct link wire from the interface unit in the boot to pin 10 on the IP - and the speedo still does not work.
The only ground I can see to the IP is pin 1. Pin 1 tested to show no ground! Found the issue!? Nope - rewired to a perfect ground - no speedo.
The car is fitted with a trip computer - which gets its information via the transducer/interface unit. This works. Reset the trip - and very quickly we register average speed and distance travelled.

Every other part of the car - and IP - work perfectly.

Have picked David Marks brain on this as well - and we are both hitting a mental brick wall.
Any flash of inspiration out there?

Cheers,
Keith

[ptjs1]

Keith,

I'd suggest that 99% of problems on facelift instruments relate to oen of 3 problems:

- the fragile circuit board
- the plug connections
- earth points

As the IP works in another car, you'd have to assume that the circuit board is ok. However it is possible that its moving very slightly and working when you put it in the 6.0 car, but cracking open a fraction when you put it back in the 4.0 car. So still a possibility. Check the continuity of the board from the connector pin up to the speedo itself.

The same principle applies to the earth points on the IP itself. Again if it works in another car, then you'd assume ok. The same should apply to the plug connections. But I'd still check them again.

However, the bulkhead earth points can definitely cause problems with the IP. I've seen a number of problems with low reading minor gauges caused by those bulkhead points. So, it could possible also affect the speedo. Even if they look intact, they can fall apart when you dismantle them. And if you've been welding in that area, it may have caused problems. As you probably know, you'll find both earth and positive terminals on both sides of the bulkhead. Take them all apart, check and rebuild. Maybe worth a look.

Cheers

Paul

[steve_m]

Do what I did when mine failed: fit a Satnav!
Was any other work carried out that could have disturbed the pickup?
I have an earlier car where the pick up is in the differential (like an ABS reluctor ring) but I think that the later ones were gearbox mounted.
Was the battery disconnected during the welding because that will fry the crap out of all sorts of electrical stuff.
I know that I have a problem with the big multi plug that connects the panel to the loom but if you have done a direct feed then it probably isn't that.
It sounds to me like an earthing problem.
Or maybe it's just that time of the month....

[XjRestorations]

An update - nothing good.
A good deal of time spent on the phone with Paul as well - we are a bit lost.
All points check out perfectly.
Earths are good to the IP. The earths within the IP are proven as the IP works perfectly - including speedo - in the 6.0ltr XJS on site.
The transducer and interface unit on the 4.0ltr (car with issue) works on the 6.0ltr.
Continuity from the interface unit to the pin 10 on the IP (speedo input).
Trip computer works - registers average speed and distance travelled.
To DOUBLE check - direct link from the interface unit to the IP - no speedo. Piggy back the feed to the trip computer across to the IP - still no speedo.
Really starting to loose the will now.
The speedo circuit has been essentially wired as a stand alone - and doesn't work. Every component on the 4.0ltr has been placed into a 6.0ltr car - and works.

[XjRestorations]

Sorry Steve - to confirm, this is an AJ6 engined car and still runs of the diff transducer.
The battery was disconnected, as was the ECU.
The transducer is confirmed good as it works when fitted into another car (along with all other parts)

[davidr]

The owner of this car (Steve) posted a number of serious allegations about how his car was treated whilst in Keith's care and the standard of the work. After some thought, I felt that the nature of the post was not suitable for the Forum so I have removed it.

Steve and Keith - you obviously have some issues to discuss and I would suggest that you attempt to resolve them as soon as possible. Please do not air them on this Forum.

Steve - if you are a JEC member then the Club will be happy to advise. If I can help in mediation then I would be very happy to.

[stevexjslondon2]

Thank you David , I am a JEC member.

If you can help mediate it would be much appreciated.

I have moderated part of Steve's post - Davidr

[davidr]

Steve. I have sent a message to Keith
I suggest we now take this conversation off- line
You can email me on xjs.jec@gmail.com or phone me on 07774 195661