My trip computer has flaked out and is giving erroneous stats (e.g. 976
miles on one tank of gas!)
Anybody have any ideas what to do to remedy?
How do you remove it from the dash? Thanks in advance.
Wayne Estrada
89 XJ-S Convertible
Wayne Estrada
President
Richmond NET
Internet Access * Web Site Development & Hosting * Web Programming
“The Capital for Worldwide Communications” tm
1-804-740-6100 http://www.richmond.net/http://www.Richmond.NET
Wayne, I had a problem with my trip computer and it turned out to be the
fuel interface unit attached to the ECU. I replaced mine with a used unit
at little cost and it has worked fine ever since.
The computer simply pulls out from the dash and is only held in by two
spring clips on each side,or it is on mine an 87 vintage.-----Original Message-----
From: Wayne Estrada wayne@richmond.net
To: xj-s@jag-lovers.org xj-s@jag-lovers.org
Date: 16 November 1998 19:56
Subject: [xj-s] Trip Computer
My trip computer has flaked out and is giving erroneous stats (e.g. 976
miles on one tank of gas!)Anybody have any ideas what to do to remedy?
How do you remove it from the dash? Thanks in advance.
Wayne Estrada
89 XJ-S ConvertibleWayne Estrada
President
Richmond NETInternet Access * Web Site Development & Hosting * Web Programming
“The Capital for Worldwide Communications” tm
1-804-740-6100 http://www.richmond.net/http://www.Richmond.NET
At 10:44 AM 4/17/99 -0400, Lushan@aol.com wrote:
To the list:� Has anyone taken out the in dash computer?� Did you lose
anything.� I believe that it just rides on top of the system and doesn’t
control anything.�
Bradley and List:
I have had mine out for a month now as I continue to buid this gauge inset
into my dash (pictures of the micro size gauges are on my web site). So
far no
problems with wire connectors hanging free in the dash.
Wayne Estrada
1989 XJ-S Convertible (Dorchester Grey)
1989 Vanden Plas Sedan (Alpine Green)
Richmond VA, USA
Please Visit my Jaguar Site at:
http://www.u3training.com/jaguarhttp://www.u3training.com/jaguar
1984 XJS H.E.
My car has a Trip Computer.
Can anyone tell me how it works, i.e. what do all the numbers mean, and how
do I reset the trip meter and clock?
Thanks
Graham
At 20:15 1999-12-17 -0600, Graham Murray, MCSE wrote:
1984 XJS H.E.
My car has a Trip Computer.
Congrats. If you’re really lucky, it might even work.
Can anyone tell me how it works, i.e. what do all the numbers mean, and how
do I reset the trip meter and clock?
Hold down the RESET button on the far right for several seconds, and all
figures will be reset.
To set the clock (running from memory, rather than doing it at the moment),
you’d hold down the HRS (hours) button and press and release the RESET
button (hold it down long enough to change the value, then release it - if
you hold the RESET button down too long, it’ll RESET the other
values). Same for MIN (minutes). There is no AM/PM indicator - the clock
runs a simple 12 hour cycle.
Miles/Km switch, if present switches the values between US and
Metric. Unless you have a UK model, in which case you may have Imperial
gallons. I only use mine (for what it is worth) in US mode (as the pumps
here display gallons and my odometer is miles), so the secondary units
mentioned below may be incorrect - they’re assumptions on my part:
FUEL shows amount of fuel (as metred by the ECU) consumed. Gallons or
Litres. If yours is accurrate (this seems to be the only thing truly
working on mine), this is useful for jotting down in your logbook between
fillups and noting the actual mileage from the odometer tripmetre.
INST displays instantanious economy (MPG or KM/L (I think)). The figure
may vary erratically, which is not unusual. Will usually be very low for
the first few minutes of driving (5-8 MPG), and as the engine warms up,
it’ll show a much healthier value (as much as you’re going to get with a
thirsty kitty). Go downhill, and the value will climb (because you’re not
using as much petrol). Can sometimes display ‘99’ briefly. Updates every
3-5 seconds or thereabouts.
AVE displays the running average economy. Same units as INST, but these
are average since the last RESET, and reflect economy of total distance
over total petrol used.
DIST displays distance (miles or km). If all is well, this should very
nearly be the same as your odometer tripmetre (if you reset them both at
fillups as I do). If not, then the other trip computer computations will
be inaccurrate.
AV SPEED reports the average speed. AFAIK, this is averaged over the
entire time the ignition is on, and therefore, if you spend a lot of time
idling while chatting to someone, the value will be lower.
TIME shows the clock. What a surprise.
DISP turns the display on/off. Well, at least OFF - pressing any of the
other buttons (like FUEL) will turn the display on and display that value.
RESET resets the logged values.
The trip computer has no battery backup, so if the automobile battery is
disconnected, the values will be lost. If you disconnect the battery, you
should probably RESET the unit with the RESET button just to ensure that it
is properly reset.
If you’re interested in tinkering, or an upgrade, you might want to swing
by my Trip Computer project page:
<http://jaguar.professional.org/TripComputer/tc.html>
I havent begun the project yet, but the basic idea is to replace the unit
with a more visually appealing one, but also one which can optionally be
used to interface to a number of projects people have discussed in these
forums.
— http://jaguar.professional.org/
Sean Straw '88 Jaguar XJSC 5.3L V12 (LHD)
Marin County, California '69 Buick GranSport 455 V8
“Graham Murray, MCSE” wrote:
1984 XJS H.E.
My car has a Trip Computer.
Can anyone tell me how it works, i.e. what do all the numbers mean, and how
do I reset the trip meter and clock?Thanks
Graham
Graham,
FUEL : Fuel consumed since reset
INST : Current fuel consumption
AVE : Fuel consumption since reset
DIST : Distance traveled since reset
AVG SPD : Average speed since reset
TIME : Press to display time of day, press
again to display time since reset
DISP : Switches off display, but all calculations
continue
RESET : Press for 5 seconds to reset functions
(except time of day)
Walter
FUEL : Fuel consumed since reset
INST : Current fuel consumption
AVE : Fuel consumption since reset
DIST : Distance traveled since reset
AVG SPD : Average speed since reset
TIME : Press to display time of day, press
again to display time since reset
DISP : Switches off display, but all calculations
continue
RESET : Press for 5 seconds to reset functions
(except time of day)
OK, Walter, explain this:
My 1986 trip computer, does not AFAIK display fault codes.
Last night when I started the car, it displayed for about one second “uuo88”
before reverting to showing the time.
Perhaps it is practicing for Y2k?
regards,
MikeFrom: Walter Petermann
Mike Morrin wrote:
From: Walter Petermann
FUEL : Fuel consumed since reset
INST : Current fuel consumption
AVE : Fuel consumption since reset
DIST : Distance traveled since reset
AVG SPD : Average speed since reset
TIME : Press to display time of day, press
again to display time since reset
DISP : Switches off display, but all calculations
continue
RESET : Press for 5 seconds to reset functions
(except time of day)OK, Walter, explain this:
My 1986 trip computer, does not AFAIK display fault codes.
Last night when I started the car, it displayed for about one second “uuo88”
before reverting to showing the time.Perhaps it is practicing for Y2k?
regards,
Mike
Mike,
I think it’s practicing to conk out altogether. The garbled
display might have something to do with resetting the serial
input display chip.
When you turn the ignition off, I assume the power to the display
chip is removed. On start up, the data in the chip is invalid.
There ‘should’ be a blanking input to disable the output of the
chip until it gets good data from the uP. Maybe this input is bad.
I’ll check it next time I have one that behaves that way. Usually
I just resolder everything, then go from there. As far as I can
remember, I haven’t seen this problem after having resoldered
everything.
Walter
How can I find out how to operate the trip computer on my 85 XJ-S. What do
all the buttons do (apart from the obvious ones like the clock.) What does
the fuel bits indicate, and is it in l/100 km or what?
Does anyone have an owners manual scanned or where can I borrow a manual to
copy. I live in Brisbane, Australia.
Iain Burgess
85 XJ-S*****************************************************************************
This email and any files transmitted with it are confidential and
intended for use by the Addressee only. The confidential nature
of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.
Use or dissemination of the information contained in the email
and/or files by a recipient other than the Addressee may cause
commercial damage to both/either the Sender and/or Addressee.
If you are not the Addressee of this email/files please immediately
contact the Sender and delete this email/files.
How can I find out how to operate the trip computer on my 85 XJ-S. What do
all the buttons do (apart from the obvious ones like the clock.) What does
the fuel bits indicate, and is it in l/100 km or what?
Mine’s an '85 also.
There’s a switch on the upper left corner marked MLS/KM. That switches
between miles and kilometers. Mine uses gallons and can’t be changed. I
don’t know whether Jaguar reprogrammed the computer for metric markets.
FUEL: Displays the amount of fuel consumed since the computer was last
reset. Mine tends to be within ~1 gal of actual, not bad. I hear others
are way off though.
INST: Instantaneous fuel economy. Kinda fun to watch.
AVE: Average fuel economy since the last time the computer was
reset. Reasonably accurate for a general guide.
DIST: Distance travelled since the computer was last reset.
AV.SPD: Average speed since the computer was last reset.
TIME: When you first push this button it will display the elapsed time
from the computer’s last reset. It will then switch to a clock. When you
first start the car it defaults to the clock.
DISP: Turns the display on or off.
RESET: the reset button. To clear all settings but the clock, put the
computer in any mode other than the clock, push and hold the reset button
for about 5 seconds. Everything will revert to zero. To change the time on
the clock, push and hold the RESET button. Then advance the hours using
the TIME button and the minutes with the DISP button.
Cheers,
Bry
Thanks, it came out great. Now the thing has stopped working properly.
When I press any of the three fuel buttons, it shows “199” in all modes
including the clock. If I switch the display off, it can read the clock,
the Ave speed, Dist, but pressing the next one sends it off to “199”. It
has only started doing this since I filled up and pressed the reset button,
before that, everything seemed to work. Anyone got any ideas?
Iain Burgess
85 XJ-S-----Original Message-----
From: Barney Dykes [mailto:bdykes@datastar.net]
Sent: Tuesday, 25 July 2000 23:32
To: Iain Burgess
Subject: Re: [xj-s] Trip Computer
Hi Iain,
Attached is the page from the 1986 XJS owner’s manual covering the operation
of the trip computer. It should print out pretty clear. Hope this helps.
I’d loan you my manual, but I live in Southern MIssissippi, USA.
Regards,
Barney Dykes ('86 XJS)
-----Original Message-----
From: Iain Burgess <@Iain_Burgess>
To: ‘xj-s@jag-lovers.org’ xj-s@jag-lovers.org
Date: Tuesday, July 25, 2000 2:31 AM
Subject: [xj-s] Trip Computer
How can I find out how to operate the trip computer on my 85 XJ-S. What do
all the buttons do (apart from the obvious ones like the clock.) What does
the fuel bits indicate, and is it in l/100 km or what?Does anyone have an owners manual scanned or where can I borrow a manual to
copy. I live in Brisbane, Australia.Iain Burgess
85 XJ-S
**
This email and any files transmitted with it are confidential and
intended for use by the Addressee only. The confidential nature
of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.Use or dissemination of the information contained in the email
and/or files by a recipient other than the Addressee may cause
commercial damage to both/either the Sender and/or Addressee.If you are not the Addressee of this email/files please immediately
contact the Sender and delete this email/files.
**
This email and any files transmitted with it are confidential and
intended for use by the Addressee only. The confidential nature
of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.
Use or dissemination of the information contained in the email
and/or files by a recipient other than the Addressee may cause
commercial damage to both/either the Sender and/or Addressee.
If you are not the Addressee of this email/files please immediately
contact the Sender and delete this email/files.
Iain,
I can photocopy the owners manual for my 1988 XJ-S V12 (Australian-delivered) if
that would be of interest. I am not sure how much difference there is between
'85 and '88 models. Let me know your postal address if you want me to proceed.
Regards,
John Rickman
1988 XJ-S V12 Coupe
Iain Burgess wrote:> How can I find out how to operate the trip computer on my 85 XJ-S. What do
all the buttons do (apart from the obvious ones like the clock.) What does
the fuel bits indicate, and is it in l/100 km or what?Does anyone have an owners manual scanned or where can I borrow a manual to
copy. I live in Brisbane, Australia.Iain Burgess
85 XJ-S
This email and any files transmitted with it are confidential and
intended for use by the Addressee only. The confidential nature
of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.Use or dissemination of the information contained in the email
and/or files by a recipient other than the Addressee may cause
commercial damage to both/either the Sender and/or Addressee.If you are not the Addressee of this email/files please immediately
contact the Sender and delete this email/files.
Thanks for all the replies on my erratic trip computer. It is working now,
occasionally. I have noticed a number of other things as well:
Strangely enough, the computer worked fine when I was stuck in traffic for
an hour, in the rain, wipers and headlights on, and fans coming on every
minute or so. Rpm seldom rose above 1000rpm in dead crawl traffic. The
charge gauge would move about two needle width down when the fans came on.
Five minutes of 1500rpm driving and it was back up to the middle.
I am beginning to suspect either the earthing of the harness under the dash,
or the power to the instruments - possibly the fuse. I will clean of the
contacts on the fuse box and replace the fuse with a gold plated one (you
can get them from the upmarket car sound stores. I will also connect a new
earth to the trip computer. and instrument panel.
As a result of the 199l/100km fuel consumption, the computer believed I used
800lt of fuel driving home last night - could be some sort of world record?
Anyone have a flash of inspiration?
Iain Burgess
85 XJ-S*****************************************************************************
This email and any files transmitted with it are confidential and
intended for use by the Addressee only. The confidential nature
of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.
Use or dissemination of the information contained in the email
and/or files by a recipient other than the Addressee may cause
commercial damage to both/either the Sender and/or Addressee.
If you are not the Addressee of this email/files please immediately
contact the Sender and delete this email/files.
Despite my best efforts, I still cannot get the fuel consumption part of my
trip computer to work properly.
The symptoms are as follows:
I replaced the OP Amp as per the book - this did not make any difference, I
bought 2 IC’s and an IC socket, and have swapped both around so I think I
can rule out the OP Amp.
I have checked all the connections under the dash and in the boot, no
difference.
I suspect that something in the sender unit circuit is getting hot, then
failing, but can’t find anything hot inside the sender unit.
Do any of the electronic experts out there know how the fuel usage part of
the computer works, and how the sender unit in the boot takes the signals
from the EU and converts it into something the trip computer can read.
I’m fairly sure that there is a simple solution, like a bad transistor or
diode that could easily be replaced.
There cannot be more than $10 worth of components in the sender unit. My
last resort is to just unsolder them all, one by one and replace the lot.
But as I have had quite a few of list comments of how others have similar
problems with their trip computers, it would be nice to see how to fix it
with the minimal of fuss.
Iain Burgess
85 XJ-S UK Spec
Brisbane Australia.*****************************************************************************
This email and any files transmitted with it are confidential and
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of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.
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At 08:14 2001-08-23 +1000, Iain Burgess wrote:
Early in the morning, the instant reading is correct , but afterabout 1/2 hour of driving, it goes to 199 again.
Sounds like a thermal problem - possibly something shorting out as the
metal near it expands with heat?
I replaced the OP Amp as per the book - this did not make any difference, I
bought 2 IC’s and an IC socket, and have swapped both around so I think I
can rule out the OP Amp.
Damn, I really wish I had a good reference for what the fuel and speed
signals should look like on a scope (the trip computer on my 1988 is iffy
with distance, but seems okay with fuel, and I’m not sure it is the head
unit itself (I’ve thought about swapping it to the 1985 and seeing if that
car reads any different with it, but I haven’t gotten around to it). If
we’d produce a chart of standard waveforms (or metre readings), some of
these things would be made much easier to diagnose.
The Trip Computer expert, Walter Petermann, hasn’t been on the list in some
time (he’s busy getting WORK done - he runs an electronics repair shop
specializing in Jaguar electrics). If you get to the point of thinking you
need to send the unit in for calibration or repair, his contact info is on
my resources page.
Do any of the electronic experts out there know how the fuel usage part of
the computer works, and how the sender unit in the boot takes the signals
from the EU and converts it into something the trip computer can read.
I had the general impression that it was pretty much a standard pulse width
modulation signal. Measure the “on” time as a function of maximum fuel
flow for the injectors (gph, or in your case, lph), and you have some idea
of fuel consumption.
There cannot be more than $10 worth of components in the sender unit. My
last resort is to just unsolder them all, one by one and replace the lot.
Again, having reference signals would make this much easier to diagnose -
one could make a 555 timer circuit (like US$1.00 in parts) to pulse the
fuel input and watch the output of the sender to see if it matches what it
should show for that input. Similar technique could be applied to the trip
computer head unit.
When I get around to swapping my trip computer head units between my cars
to confirm where my problem lies, I’ll see about measuring these signals
and producing a simple circuit for simulating the input. That won’t do you
much good now, but perhaps you’ll beat me to it, and I won’t have to do the
work.
— http://jaguar.professional.org/
Sean Straw '88 Jaguar XJSC 5.3L V12 (LHD) ‘Black Cat’ 63K
Marin County, California '85 Jaguar XJS 5.3L V12 (LHD) ‘Bad Kitty’ 210K
'69 Buick GranSport 455 V8 324K
At 04:22 PM 08/22/2001 -0700, you wrote:
Damn, I really wish I had a good reference for what the fuel and speed
signals should look like on a scope (the trip computer on my 1988 is
iffy with distance, but seems okay with fuel, and I’m not sure it is the
head unit itself (I’ve thought about swapping it to the 1985 and seeing if
that car reads any different with it, but I haven’t gotten around to
it). If we’d produce a chart of standard waveforms (or metre readings),
some of these things would be made much easier to diagnose.
Sean
Don’t know if this will help or not. It’s from something else I’m doing
with an XJ6
"The Trip Computer in the dash is a nice clock without information from the
speedometer, and the fuel injection system. The speedometer feed provides
speed and distance information but the ECU doesn’t connect to the Trip
Computer. Rather, the ECU is connected to the Interface Unit which is
located adjacent to the ECU in the trunk. The Interface Unit actually
creates and sends the fuel flow information to the Trip Computer.
The three units work together in sequence. The Jag ECU generates an
injector pulse which is sent to the injectors and the Interface Unit
simultaneously. The Interface Unit takes the voltage of the injector pulse
and derives a consistent measured voltage which is linearly related to the
full duty cycle of the injectors. That “control” voltage in turn drives a
variable frequency generator which then sends square waves at variable
frequencies to the Trip Computer. The Trip Computer decodes those
frequencies into pulses which increment a fuel consumption register. Given
enough increments the Trip Computer reads out fuel consumption in 1/10ths.
of a gallon increments. MPG is derived by dividing fuel consumption by the
distance information contained in a separate register.
Testing the XJ6 system in place was the next step. To test the function of
the interface the ignition was turned “ON” but the vehicle not
started. This caused the Trip Computer to increment at a rate of
approximately 18.5 gph. This meant that, absent an ECU pulse, and
operating on a 12vdc line feed, the Interface Unit was sending a constant
signal to the Trip Computer. My cohort determined the signal was a fixed
250 HZ. Obviously this was the base frequency representing constant full
duty cycle flow of six Jag injectors. Subsequent vehicle road testing with
the ECU/Interface Unit connection eliminated (unplug the Y/G wire) , gave
an indicated flow rate of 20.65 gph. This difference between 18.5 and
20.65 gph was thought to be due to higher voltage and yielded a base
frequency of approximately 274 HZ."
Clearly working with your 5.3 the base frequency will be higher and I would
guess would result in a GPH full duty cycle flow rate of about 34 gallons
per hour (calculated for twelve cylinders from 5.3 injector tech
specs). In vehicle testing should be doable using the procedure
above. The key point is that the interface unit output is a square wave
which with your skill (unlike mine) you should be able to measure. My tech
friends tell me that speedometer signals are also square wave signals.
Wes Channell
Hi,Iam new to the list and enjoy it vevy much.If some one can help me,I have
a 87 xjs and need a trip computer can enyone help,Paul
At 08:14 2001-08-23 +1000, Iain Burgess wrote:
Early in the morning, the instant reading is correct , but afterabout 1/2 hour of driving, it goes to 199 again.
Sounds like a thermal problem - possibly something shorting out as the
metal near it expands with heat?I replaced the OP Amp as per the book - this did not make any
difference, I
bought 2 IC’s and an IC socket, and have swapped both around so I think
I
can rule out the OP Amp.Damn, I really wish I had a good reference for what the fuel and speed
signals should look like on a scope (the trip computer on my 1988 is
iffy
with distance, but seems okay with fuel, and I’m not sure it is the head
unit itself (I’ve thought about swapping it to the 1985 and seeing if
that
car reads any different with it, but I haven’t gotten around to it). If
we’d produce a chart of standard waveforms (or metre readings), some of
these things would be made much easier to diagnose.The Trip Computer expert, Walter Petermann, hasn’t been on the list in
some
time (he’s busy getting WORK done - he runs an electronics repair shop
specializing in Jaguar electrics). If you get to the point of thinking
you
need to send the unit in for calibration or repair, his contact info is
on
my resources page.Do any of the electronic experts out there know how the fuel usage part
of
the computer works, and how the sender unit in the boot takes the
signals
from the EU and converts it into something the trip computer can read.I had the general impression that it was pretty much a standard pulse
width
modulation signal. Measure the “on” time as a function of maximum fuel
flow for the injectors (gph, or in your case, lph), and you have some
idea
of fuel consumption.There cannot be more than $10 worth of components in the sender unit.
My
last resort is to just unsolder them all, one by one and replace the
lot.Again, having reference signals would make this much easier to diagnose -
one could make a 555 timer circuit (like US$1.00 in parts) to pulse the
fuel input and watch the output of the sender to see if it matches what
it
should show for that input. Similar technique could be applied to the
trip
computer head unit.When I get around to swapping my trip computer head units between my cars
to confirm where my problem lies, I’ll see about measuring these signals
and producing a simple circuit for simulating the input. That won’t do
you
much good now, but perhaps you’ll beat me to it, and I won’t have to do
the
work.— http://jaguar.professional.org/
Sean Straw '88 Jaguar XJSC 5.3L V12 (LHD) ‘Black Cat’
63K
Marin County, California '85 Jaguar XJS 5.3L V12 (LHD) ‘Bad Kitty’
210KOn Wed, 22 Aug 2001 16:22:26 -0700, sean.straw+Jaguar@mail.professional.org wrote:
'69 Buick GranSport 455 V8 324K
Send a cool gift with your E-Card
http://www.bluemountain.com/giftcenter/
I drive a 1976 xj-s… a trip computer would only depress me 
'76 Jurgen
paul garnett
<mrcobra11@exci To: sean.straw+Jaguar@mail.professional.org, xj-s@jag-lovers.org
te.com> cc:
Sent by: Subject: Re: [xj-s] Trip Computer
owner-xj-s@jag-
lovers.org
23/08/2001
13:50
Hi,Iam new to the list and enjoy it vevy much.If some one can help me,I
have
a 87 xjs and need a trip computer can enyone help,Paul
At 08:14 2001-08-23 +1000, Iain Burgess wrote:
Early in the morning, the instant reading is correct , but
after
about 1/2 hour of driving, it goes to 199 again.
Sounds like a thermal problem - possibly something shorting out as the
metal near it expands with heat?I replaced the OP Amp as per the book - this did not make any
difference, I
bought 2 IC’s and an IC socket, and have swapped both around so I think
I
can rule out the OP Amp.Damn, I really wish I had a good reference for what the fuel and speed
signals should look like on a scope (the trip computer on my 1988 is
iffy
with distance, but seems okay with fuel, and I’m not sure it is the head
unit itself (I’ve thought about swapping it to the 1985 and seeing if
that
car reads any different with it, but I haven’t gotten around to it). If
we’d produce a chart of standard waveforms (or metre readings), some of
these things would be made much easier to diagnose.The Trip Computer expert, Walter Petermann, hasn’t been on the list in
some
time (he’s busy getting WORK done - he runs an electronics repair shop
specializing in Jaguar electrics). If you get to the point of thinking
you
need to send the unit in for calibration or repair, his contact info is
on
my resources page.Do any of the electronic experts out there know how the fuel usage part
of
the computer works, and how the sender unit in the boot takes the
signals
from the EU and converts it into something the trip computer can read.I had the general impression that it was pretty much a standard pulse
width
modulation signal. Measure the “on” time as a function of maximum fuel
flow for the injectors (gph, or in your case, lph), and you have some
idea
of fuel consumption.There cannot be more than $10 worth of components in the sender unit.
My
last resort is to just unsolder them all, one by one and replace the
lot.On Wed, 22 Aug 2001 16:22:26 -0700, sean.straw+Jaguar@mail.professional.org wrote:Again, having reference signals would make this much easier to diagnose
one could make a 555 timer circuit (like US$1.00 in parts) to pulse the
fuel input and watch the output of the sender to see if it matches what
it
should show for that input. Similar technique could be applied to the
trip
computer head unit.When I get around to swapping my trip computer head units between my
cars
to confirm where my problem lies, I’ll see about measuring these signals
and producing a simple circuit for simulating the input. That won’t do
you
much good now, but perhaps you’ll beat me to it, and I won’t have to do
the
work.— http://jaguar.professional.org/
Sean Straw '88 Jaguar XJSC 5.3L V12 (LHD) ‘Black Cat’
63K
Marin County, California '85 Jaguar XJS 5.3L V12 (LHD) ‘Bad Kitty’
210K
'69 Buick GranSport 455 V8 324K
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I tested the trip computer as you recommended - With the ignition on but not
started, I get 1.4 Gallons in 1 minute reading which is around 84 Gal/hour.
Driving all the way home, I got 24.5G in 17 minutes which gives me
86.7Gal/Hour (the 17 minutes is not exact).
I will re-check the wiring between the ECU and the sender unit, but it looks
like I have a lot more “theoretical fuel” usage than the 18.5 Gal/hour.
Would mine being a UK spec car make that much difference.
The ECU is obviously not giving out a continuos duty cycle to the injectors,
so I am back to suspecting the sender unit.
Does the square wave frequency get faster with more fuel used or slower, if
I am using maximum fuel, would it be that the square wave is just
continually “on” thus fooling the Trip computer into thinking it is
infinitely high frequency hence lots fuel being used. If that is the case,
which one of the components in the sender unit is likely to produce this
effect?
Iain Burgess
85 XJ-S UK Spec
Brisbane Australia-----Original Message-----
From: channell@cvc.net [mailto:channell@cvc.net]
Sent: Thursday, 23 August 2001 10:08
To: Iain Burgess
Subject: Re: [xj-s] Trip Computer
Do any of the electronic experts out there know how the fuel usage part of
the computer works, and how the sender unit in the boot takes the signals
from the EU and converts it into something the trip computer can read.I’m fairly sure that there is a simple solution, like a bad transistor or
diode that could easily be replaced.
I don’t understand the electronics but can give you the logic flow. The
trip computer interface unit gets a signal from the ECU which corresponds
to the injector pulse. Actually two terminals in the ECU are jumpered
together so that the signal goes both places. The trip computer interface
generates a square wave signal which is fixed at some HZ when voltage is
applied. The injector voltage causes a variation in the frequency of the
square wave. The trip computer simple updates the fuel register by one
unit every time it receives a square wave. After so many updates it
increments the diaplay by 1/10 of a gallon.
A quick test is to turn on the key but not start the engine. The trip
computer fuel function should increment at a rate of about 18.5 gallons per
hour. Next unplug the y/g wire from the ECU to the interface box. The
trip computer should increment the fuel function at a fixed rate similar to
what you saw with the ignition on test. This amount represents the full
duty cycle flow of the six Jag injectors. If after driving for a while the
TC continues to increment at a consistent rate I would look at the wiring
between the ECU and the interface or the connections inside either. If the
interface fails to produce full duty cycle readings on the TC my guess is
the interface unit itself.
Wes Channell
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My distance reading on the TC is very accurate (exactly what is shown on the
speedo that is).
I have looked any possibility of shorts, could not see any point where it
could.
Does the fuel input pulse to the sender unit, or is it a voltage that varies
which the sender unit then changes to a series of pulses whose frequency
then varies?
I could built a 555 frequency generator (you could also use it as an input
for the speedo, and take a photo of your speedo indicating 260kph - would
look good on those websites that brag about top speeds. You would have to
rev it a bit to make it look authentic)
That would test the Trip computer unit, and then I would know if the sender
unit was not working, or the TC unit.
I anyone around the Brisbane area has a spare sender unit, I could also test
it that way.
Iain Burgess
85 XJ-S UK Spec
Brisbane Australia
<<<<< Sean wroteDate: Wed, 22 Aug 2001 16:22:26 -0700
From: sean.straw+Jaguar@mail.professional.org (Sean Straw)
Subject: Re: [xj-s] Trip Computer
At 08:14 2001-08-23 +1000, Iain Burgess wrote:
Early in the morning, the instant reading is correct , but afterabout 1/2 hour of driving, it goes to 199 again.
Sounds like a thermal problem - possibly something shorting out as the
metal near it expands with heat?
I replaced the OP Amp as per the book - this did not make any difference, I
bought 2 IC’s and an IC socket, and have swapped both around so I think I
can rule out the OP Amp.
Damn, I really wish I had a good reference for what the fuel and speed
signals should look like on a scope (the trip computer on my 1988 is iffy
with distance, but seems okay with fuel, and I’m not sure it is the head
unit itself (I’ve thought about swapping it to the 1985 and seeing if that
car reads any different with it, but I haven’t gotten around to it). If
we’d produce a chart of standard waveforms (or metre readings), some of
these things would be made much easier to diagnose.
The Trip Computer expert, Walter Petermann, hasn’t been on the list in some
time (he’s busy getting WORK done - he runs an electronics repair shop
specializing in Jaguar electrics). If you get to the point of thinking you
need to send the unit in for calibration or repair, his contact info is on
my resources page.
Do any of the electronic experts out there know how the fuel usage part of
the computer works, and how the sender unit in the boot takes the signals
from the EU and converts it into something the trip computer can read.
I had the general impression that it was pretty much a standard pulse width
modulation signal. Measure the “on” time as a function of maximum fuel
flow for the injectors (gph, or in your case, lph), and you have some idea
of fuel consumption.
There cannot be more than $10 worth of components in the sender unit. My
last resort is to just unsolder them all, one by one and replace the lot.
Again, having reference signals would make this much easier to diagnose -
one could make a 555 timer circuit (like US$1.00 in parts) to pulse the
fuel input and watch the output of the sender to see if it matches what it
should show for that input. Similar technique could be applied to the trip
computer head unit.
When I get around to swapping my trip computer head units between my cars
to confirm where my problem lies, I’ll see about measuring these signals
and producing a simple circuit for simulating the input. That won’t do you
much good now, but perhaps you’ll beat me to it, and I won’t have to do the
work.
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intended for use by the Addressee only. The confidential nature
of the information contained in the email and/or file is not waived,
lost or destroyed if it is sent in error to other than the Addressee.
Use or dissemination of the information contained in the email
and/or files by a recipient other than the Addressee may cause
commercial damage to both/either the Sender and/or Addressee.
If you are not the Addressee of this email/files please immediately
contact the Sender and delete this email/files.