[xj] Trip computer

I’ve had my 83 XJ6lll for a couple of months and love it.
I think I’ve solved my fuel odor problem by tightening up a couple of lines.
Now I’d like to try to get the trip computer working. It seems to be working
so far as distance travelled goes, but the fuel section gives me odd readings.
The fuel consumed reading for the trip is way too high and when I press
instant I either get a reading of 0 or 99, and average gives me a 0.
I’d appreciate any suggestions.
Thanks, and a Happy New Year to all.
Jay Friday

The 0 reading on instantaneous and average is due to the fact that the speed
input information is non-existent.

My computer did exactly the same and it was due to an intermittent
connection.

The average consumption data is calculated internally using the distance and
speed inputs (which input-speed-is used to calculate distance by utilising
the elapsed time record…push your “time” button twice and you will have an
elapsed time reading of all the minutes/hours the engine was running since
the last reset.)

So, if the speed input is duff, the distance and average speed/fuel
consumption information is out of whack.

What is more, my computer was glowing three or four buttons dimly and not
reading anything at all (members of the list know it was one of the problems
in my car which we decided to put on the “to do” list.)

I pulled the computer from the dash and disconnected the two 3-pin
connectors at the rear. This totally disconnected all power to the unit
which allowed it to clear its befuddled memory circuits. WHile it was
calculating nothing at all, I cleaned the connectors and checked for power
feed to the unit (3 feeds, purple wire, green wire and red wire) All present
and correct.

Re-fitted the unit and I now have good readings again and all functions are
working well. Apparently the trip computer uses the same pulse-generator for
speed inputs as the speedo and cruise control (i.e. in the gearbox) If your
speedo needle wanders a bit, or gives eadings about 8-10 mph slow, then the
pulse generator is tired and must be renewed.

Good hunting

Mark Young
Johannesburg, South Africa
1983 Daimler DOuble SIx Series III V12 HE Van Den Plas 180 000km
1972 Series I 4.2 XJ6 SWB restoration project

I have a XJ12 Sovereign 1988 and after a jump in the battery to
start the engine, the trip computer stoped showing any information,
showing only a sequence o 88 88 88 88. Any clue on how to fix it?–
Rubens - Zambia - XJ12
Kitwe, Zambia
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Rubens Figueiredo wrote:

I have a XJ12 Sovereign 1988 and after a jump in the battery to
start the engine, the trip computer stoped showing any information,
showing only a sequence o 88 88 88 88. Any clue on how to fix it?

The jumpstart may, somewhat unusually, have fried it, Rubens - it’s the
common computer fault code…

However, have you tried driving the car, pressing and holding the
reset button for some 10+ seconds. Then tried various buttons for any
indications? As the display is on, the computer obviously gets some
power, but depending on reactions to the various buttons one of the
power inputs may have blown a fuse…

You can also disconnect and reconnect the battery. Though efficaceous to
shake some sense into computers generally it may or may not work on a
Jag driving computer too…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Frank Andersen sent Tue 9 Mar 2004:

I’ve had a few strange readings on my computer but it always seems
to fix itself after a few days.–
glenn britnell
Lancashire, United Kingdom
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To all,

Has anyone had display issues with their trip computers ? I have
taken mine apart, cleaned the switch contacts, inspected for loose
wires, etc. I still have a display that works only part of the time.
These things don’t seem that complicated. Is there somthing else I
should check? Do they need to be grounded to the dash panel?
Please let me know what you guys think.
Thanks,
Tim.–
Tim '83 VDP
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Even when working, it’s unreadable in Calif sun!
;]–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Tim. wrote:

To all,

Has anyone had display issues with their trip computers ? I have
taken mine apart, cleaned the switch contacts, inspected for loose
wires, etc. I still have a display that works only part of the time.
These things don’t seem that complicated. Is there somthing else I
should check? Do they need to be grounded to the dash panel?
Please let me know what you guys think.
Thanks,
Tim.

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In reply to a message from Tim. sent Tue 30 Oct 2007:

Tim

I’m not sure if it will help but have you looked here?

http://www.backglass.org/duncan/jag/ifu/--
The original message included these comments:

Has anyone had display issues with their trip computers ? I have
taken mine apart, cleaned the switch contacts, inspected for loose


al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom
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In reply to a message from Tim. sent Tue 30 Oct 2007:

Tim,

I had problems with my trip computer. The unit was intermittent and
would re-set at times. This is what I did to cure the problems:

  1. Took the unit apart and found that the wires that are soldered
    down to the PCB needed to be taken out and re-soldered becuase they
    were corroded. I also replaced the small wire wound resitor on the
    board (I think it was 56 Ohms 3 watts). The resistor apeared to be
    suspect.
  2. The second problem was that the connection at the fuse holder
    was loose and also corroded. I dropped the fuse box cleaned and
    soldered the wire to the rear of the fuse clip.

It took me several goes to get it all fixed as it should be but
it’s been fine now for a couple of years or so.

Cheers

Len.

1985 VDP at 205K miles.–
The original message included these comments:

To all,
Has anyone had display issues with their trip computers ? I have
taken mine apart, cleaned the switch contacts, inspected for loose
wires, etc. I still have a display that works only part of the time.
These things don’t seem that complicated. Is there somthing else I
should check? Do they need to be grounded to the dash panel?
Please let me know what you guys think.
Thanks,
Tim.

Tim '83 VDP


Len Dole
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In reply to a message from Len Dole sent Tue 30 Oct 2007:

what has worked for me is to have a fully charged battery, or to
disconnect the battery cables for 20 minutes and re-connect them,
it always resuscitates the display.

Zurdo–
The original message included these comments:

I had problems with my trip computer. The unit was intermittent and
would re-set at times. This is what I did to cure the problems:
Len.


1965 3.8 ‘S’ 1984 XJ-6
Florida, United States
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In reply to a message from Len Dole sent Tue 30 Oct 2007:

Al and Len,
Both are a huge help! Thank you!

Al, your diagrams are great.

I will let you know how I make out.
Tim.–
The original message included these comments:

  1. Took the unit apart and found that the wires that are soldered
    down to the PCB needed to be taken out and re-soldered becuase they
    were corroded. I also replaced the small wire wound resitor on the
    board (I think it was 56 Ohms 3 watts). The resistor apeared to be
    suspect.
  2. The second problem was that the connection at the fuse holder
    was loose and also corroded. I dropped the fuse box cleaned and
    soldered the wire to the rear of the fuse clip.
    It took me several goes to get it all fixed as it should be but
    it’s been fine now for a couple of years or so.
    Cheers


Tim '83 VDP
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In reply to a message from almcl sent Tue 30 Oct 2007:

Al,
Thank you for the great info in the trip computer. I know what
I’ll be doing wuth my next free day.
Stephen J. Niznik–
The original message included these comments:

I’m not sure if it will help but have you looked here?
http://www.backglass.org/duncan/jag/ifu/
The original message included these comments:

Has anyone had display issues with their trip computers ? I have
taken mine apart, cleaned the switch contacts, inspected for loose


dizmando
jefferson hills PA, United States
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Cannara wrote:

Even when working, it’s unreadable in Calif sun!
;]

It’s b… unreadably in any sun, anywhere Alex…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Tim. sent Tue 30 Oct 2007:

Thanks, Tim.

Glad they were of use but I can’t take the credit: they were
actually produced by Duncan Brown (Frobozz) who used to post here
regularly.

His latest project, which is still ongoing, was to produce an Air
Con amplifier replacement for under $30. Hope to hear of his
success soon.–
The original message included these comments:

Al, your diagrams are great.
I will let you know how I make out.


al mclean '93 XJS 4.0 - '84 4.2 Daimler - '84 DD6
Telford, United Kingdom
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Tim. wrote:

To all,

Has anyone had display issues with their trip computers ? I have
taken mine apart, cleaned the switch contacts, inspected for loose
wires, etc. I still have a display that works only part of the time.
These things don’t seem that complicated. Is there somthing else I
should check? Do they need to be grounded to the dash panel?
Please let me know what you guys think.

All electrics need a ground, Tim - so in addition to internal
examinations…

Incidentally; you don’t mention if the computer itself actually works,
ie show correct when the display is on. Or, like, retain memory if the
display goes off. - it may just be a display thing, simplifying
matters…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Frank Andersen sent Wed 31 Oct 2007:

Frank,
The computer itself works just fine. I will retain the memory and
everything. It seems that it is just the display that has issues.
The MPG calculation is really quite accurate when compared to the
math calculations. The clock keeps very good time, when I can read
it.

Tim.–
The original message included these comments:

Incidentally; you don’t mention if the computer itself actually works,
ie show correct when the display is on. Or, like, retain memory if the
display goes off. - it may just be a display thing, simplifying
matters…:slight_smile:
Frank


Tim '83 VDP
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Tim. wrote:

In reply to a message from Frank Andersen sent Wed 31 Oct 2007:

Frank,
The computer itself works just fine. I will retain the memory and
everything. It seems that it is just the display that has issues.
The MPG calculation is really quite accurate when compared to the
math calculations. The clock keeps very good time, when I can read
it.

It may be just a display fault then, Tim - not that that clarifies the
specific cause or remedy…:slight_smile:

Frank
xj6 85 Sov Europe (UK/NZ)===================================================
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In reply to a message from Frank Andersen sent Wed 31 Oct 2007:

I think, now that I have the wiring diagram, I will hook power to
it and bench test it. IMHO, it is loose connections inside. If I
apply pressure to certian areas of the outside case I get diffrent
reactions from the display, ie, on or off.

Funniest thing is, when I drive moderate distances, over ten or
twenty miles it seems to work just fine.–
The original message included these comments:

It may be just a display fault then, Tim - not that that clarifies the
specific cause or remedy…:slight_smile:
Frank


Tim '83 VDP
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You might look over how the display connects to the main board. These
connections are termed ‘dry’, in that they involve very low currents and
perhaps low voltages, so any corrosion does them in easily. The clock in our
86 Accord started doing funny display things last year, and whacking it no
longer did the trick, so it had to come out and get those connections cleaned.–
Alex
79xj6L SII (BRG + wires)
86xj6 SIII (Black)
61 Sprite MkII (Red)
Menlo Park, Calif.

Tim. wrote:

In reply to a message from Frank Andersen sent Wed 31 Oct 2007:

Frank,
The computer itself works just fine. I will retain the memory and
everything. It seems that it is just the display that has issues.
The MPG calculation is really quite accurate when compared to the
math calculations. The clock keeps very good time, when I can read
it.

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My trip computer works sometimes.but don’t work when
pushing buttons. Is this a common problem. Is this unit
connected to main ECU? Is there a trick to fix connector
shorts, ETc any input anyone cheers–
Daniel Sawyer
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