[xj-s] Speedo problem

Hello all,

I have been working on a friends 1983 XJS and have basically
got the engine running happy enough but have come across a
potential problem. Before the car came to me it had an
engine and transmission transplant from a 1988 XJS with
Marelli ignition. The previous ‘‘Mechanic’’ that installed
the engine made a mess of the wiring when it was changed
back to a Lucas ignition. This is now fixed, but I’m not
sure if I have somewhere to plug in the speedo anymore. I
believe the donor car had the speedo transducer on the diff?
Had anyone else come up against this problem? Any ideas
would be warmly received.

Thanks
Sean–
1985 XJS HE V12
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–

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Hi Sean,

Yes, the 83 had the transducer mounted on the side of the transmission,
which sent an electrical signal directly to the speedo, while the 88 &
89 models (the Marelli ignition was first used in the middle of the 89
model run) had a speed transmitter mounted on the right rear of the
diff cover, and sent pulses picked up from diff gear teeth to a speed
interface unit in the boot, which then sent a signal to the speedo.

If the car you are working on had an operating speedo at some point
after engine/trans swap, it has to have one of those two systems. The
speed signal is also required to operate the distance functions of the
trip computer, and the cruise control. IIRC, the transducer screwed
onto the side of the transmission like an old mechanical speedo cable
(which it replaced :wink:

The speed transmitter on the rear plate of the diff is easy to spot, as
there is a coiled black wire running from the transmitter into the
boot. There is then a black speed interface mounted on the left hockey
stick in the boot (underside of top of left rear fender).

George Balthrop, Clifton, VA USA
89 and 85 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: RingoSM ringosm@gmail.com

1983 XJS…had an engine and transmission transplant from a 1988 XJS…
I’m not sure if I have somewhere to plug in the speedo anymore. I
believe the donor car had the speedo transducer on the diff?

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In reply to a message from George Balthrop sent Sun 4 Mar 2012:

Thanks George, I do believe then that this car is in a unique
configuration where there is no place for a speedo sender. This is
going to be a rather annoying problem.

Thanks for you help :slight_smile:

Sean–
1985 XJS HE V12
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
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In reply to a message from RingoSM sent Sun 4 Mar 2012:

Im ususing my gps as a speedometer dont know if anyone has tried
this. Just didnt feel like messing with speed signal transducers.–
The original message included these comments:

configuration where there is no place for a speedo sender. This is
going to be a rather annoying problem.


britirn
West Covina, California, United States
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In reply to a message from britirn sent Sun 4 Mar 2012:

This will be my work around until I can make something that will
send pulses to the speedo.

Sean–
1985 XJS HE V12
–Posted using Jag-lovers JagFORUM [forums.jag-lovers.org]–
–Support Jag-lovers - Donate at http://www.jag-lovers.org/donate04.php

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In reply to a message from RingoSM sent Sun 4 Mar 2012:

Hello all,
I have been working on a friends 1983 XJS and have basically
got the engine running happy enough but have come across a
potential problem. Before the car came to me it had an
engine and transmission transplant from a 1988 XJS with
Marelli ignition. The previous ‘‘Mechanic’’ that installed
the engine made a mess of the wiring when it was changed
back to a Lucas ignition. This is now fixed, but I’m not
sure if I have somewhere to plug in the speedo anymore. I
believe the donor car had the speedo transducer on the diff?
Had anyone else come up against this problem? Any ideas
would be warmly received.
Thanks
Sean

Sean
I have had several '88 XJS and they all had Lucas ignitions. I
think the Marelli did not start until '89. Anyway the transducer
for the speedo in on the side of the transmission. Hope that helps.
JHS–
countpackula
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In reply to a message from britirn sent Sun 4 Mar 2012:

I too have been using my GPS instead of the speedo or to check the
speedo. Cool idea.
JHS–
countpackula
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In reply to a message from countpackula sent Sun 4 Mar 2012:

When using the GPS, how did your speedo compare…mine is out about
20% on the low side. No wonder I was passing everybody lol–
The original message included these comments:

I too have been using my GPS instead of the speedo or to check the
speedo. Cool idea.


Bill 87 TWR XJS Ontario, Canada
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