The MPG feature on my trip computer in my 1994 XJS V12 has started
functioning backwards!
If I am cruising down the Interstate at 75 MPH in 6th gear my MPG
read out shows I am getting 8 MPG. It used to show about 23 MPG.
Conversely, if I am accelerating hard up through the gear, it
indicates 30+ MPG. ???
Not sure about yours, but older XJSs had a “interface unit” that converted
injector pulse width into a language the trip computer could understand. My
gut feeling is that this could be the problem.
But I suspect others will chime in will better answers
Doug Dwyer
Longview Washington USA
1995 XJR
The MPG feature on my trip computer in my 1994 XJS V12 has started
functioning backwards!
Apparently beginning with the 92 V-12 models (and probably any earlier
4.0L-engined models) there was no longer a separate fuel interface, but
rather the Engine Management ECU provides the “fuel used” output to the
trip computer via a Yellow/Green wire.
Might also check the trip computer ground (Black wire).
George Balthrop, Clifton, VA USA
85 & 89 XJ-S Coupes; 89 XJ40 VDP-----Original Message-----
From: Doug Dwyer dougdwyer1@comcast.net
Not sure about yours, but older XJSs had a “interface unit” that
converted injector pulse width into a language the trip computer could
understand. My gut feeling is that this could be the problem.
In reply to a message from TheDrivenMan sent Mon 17 Nov 2008:
If you have the same mph/km switch the 94 X300s got, then you have
accidentally swapped the setting. Harder use comes up as a higher
number (litres per 100Km) whereas driving gently gives low numbers
(i.e. less fuel used). Let us know if that’s it.–
The original message included these comments:
If I am cruising down the Interstate at 75 MPH in 6th gear my MPG
read out shows I am getting 8 MPG. It used to show about 23 MPG.
Conversely, if I am accelerating hard up through the gear, it
indicates 30+ MPG. ???
What causes this?
Check that the little switch up on the left side of the trip computer
display is in the correct position. In the “mls” position it reads in
statute miles per gallon and in the “km” position it reads in liters per
kilometer (sort of the opposite if you ask me). In the “mls” position a
high number shows good fuel economy, in the “km” position I believe that
a low number shows good fuel economy.
If this just started happening and nothing else seems amiss, I suspect
that someone bumped that little switch. BTW, I’ve never done the math
for the “km” position numbers would be, so I could be wrong.
Regards,
Paul M. Novak
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1985 XJ6 Vanden Plas (parts)
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA @Paul_M_Novak1-----Original Message-----
From: owner-xj-s@jag-lovers.org [mailto:owner-xj-s@jag-lovers.org] On
Behalf Of TheDrivenMan
Sent: Monday, November 17, 2008 6:53 AM
To: xj-s@jag-lovers.org
Subject: [xj-s] Trip Computer MPG functions backwards
Hello All,
The MPG feature on my trip computer in my 1994 XJS V12 has started
functioning backwards!
If I am cruising down the Interstate at 75 MPH in 6th gear my MPG
read out shows I am getting 8 MPG. It used to show about 23 MPG.
Conversely, if I am accelerating hard up through the gear, it
indicates 30+ MPG. ???
In reply to a message from Paul M. Novak sent Mon 17 Nov 2008:
Ta-Dah!
I just went to the garage to check,and the ML/KMS button on the
lower LH side of the computer was on KMS.
Thank you fellas.–
The original message included these comments:
Check that the little switch up on the left side of the trip computer
display is in the correct position. In the ‘‘mls’’ position it reads in
statute miles per gallon and in the ‘‘km’’ position it reads in liters per
I'm glad that I could help. I wish they were all that
easy!!!
Regards,
Paul M. Novak
1990 XJ-S Classic Collection convertible
1987 XJ6 Vanden Plas
1985 XJ6 Vanden Plas (parts)
1984 XJ6 Vanden Plas
1969 E-Type FHC
1957 MK VIII Saloon
Ramona, CA @Paul_M_Novak1-----Original Message-----
From: owner-xj-s@jag-lovers.org [mailto:owner-xj-s@jag-lovers.org] On
Behalf Of TheDrivenMan
Sent: Tuesday, November 18, 2008 7:23 PM
To: xj-s@jag-lovers.org
Subject: RE: [xj-s] Trip Computer MPG functions backwards
In reply to a message from Paul M. Novak sent Mon 17 Nov 2008:
Ta-Dah!
I just went to the garage to check,and the ML/KMS button on the
lower LH side of the computer was on KMS.
Thank you fellas.
The original message included these comments:
Check that the little switch up on the left side of the trip computer
display is in the correct position. In the ‘‘mls’’ position it reads
in
statute miles per gallon and in the ‘‘km’’ position it reads in liters
per
