Hi Guys,

My dash came out to replace my evaporator however i have just noticed that the trip computer is not recording

Instant Fuel
Average

only thing it is doing is is recording time and DIstance travelled,
anybody have any idea where the sensors are so that i can check
i have checked the connecters to the schematics and it all looks wired up correctly

thanks in advance

 

No sensors per se.

There's a "Fuel Interface Module" in the boot. I don't know exactly how it works but injector pulse width info from the ECU is sent to the fuel interface module ....which in turn converts the data into something the trip computer can use.

That said, I don' t know how to determine if your problem is in the FIM or the trip computer. FWIW, I've heard of many trip computers beng replaced but can remember nary a single instance where the FIM failed <shrug>. Not 100% proof of anything, I know.

Diagnosis by substitution is one idea. The pain of guesswork should be eased by that fact that used Ser III parts are usually quite inexpensive.

Cheers
DD

 

I've had that crap happen, and someone told me to diisconnect both cables from the battery for 20 minutes, then reconnect them to see if the trip computer is "awakened". In my case, it awoke and started "reading" again.

also make sure the battery is fully charged, these Series 3 cars are very sensitive to battery voltage and if the computer detects low battery voltage, it has a tendency to go to "sleep" thinking it needs to save the planet by not drawing voltage.

I hate to say it but I really think these trip computers have a "sleep mode", so that if you let them really sleep for those 20 minutes, they awake "refreshed" after the short nap. But even if it awakens, remember that these trip computers are programmed to deliver "very optimistic" reports. So in my humble opinion, they are a very glorified, CLOCK.

 

here's a great article with pictures that has been around since the 1990's, if you want to learn about these trip computers:

Jaguar XJ6 SIII trip computer details

 

I dunno. The three I've had have been accurate within about 3% versus the speedo....which is pretty good as far as automotive gadgets go. Of course, if the speedo is, let's say, 3% off the in the same direction, the compounds :-)


Cheers
DD

 

Doug, I'm thinking of eliminating the trip computer, it just does not "fit" my idea of a classic Jag. It seems so "out of place", a digital gizmo in an otherwise analog car, and in my opinion, useless.

if I find a a Kenwood radio Equalizer (the little one with many adjustable bands), that fits in the trip computer's opening, depth and width-wise, the "computer" is gone.

I'm going to post a picture of the mods I've done so far to the vertical trip computer panel of my XJ, which brings together 1960's and 1980's Jaguars. When you consider the butchering that is going on with these cars, mine will be like "classic art" :-))

 

I say do whatever strikes your fancy :-)

However, I'm not sure an equalizer will add any vintage-ish appearance of your Jaguar interior :-)

OTOH, both the trip computer and an equalizer are very "eighties"....so perhaps neither is really out of place ?

After all, the Ser III Jag is the most modern of all antique automobiles :-)

Cheers
DD

 

I agree the EQ will not add any vintage "look" to the interior, but it will definitely add usefullness. I can't remember the last time I went thru the trip computer to look at my "average speed". It always says "Average speed 43 mph" even if I was going 80. And I know that I can get at least 530 to 545 miles out of the two tanks on an interstate trip going 70 on cruise with a/c ON, so I rely on the speedo counter anyway. (city driving is not predictable).

I think the trick is to change tank every 20 miles to keep the fuel levels and the rear "wings" balanced, just like they do in airplanes. That was the whole idea with the twin tanks which started with the S type in 1963. Funny, the S type does not have as complicated a system to change tanks as the XJ, but it does have twin fuel pumps, no fuel return valves, when you switch tanks, the switch starts the selected pump and turns the other one OFF.

 

Hi all just an update,

i managed to get hold of a replacement module hooked it all up and started readin and recording with no issues at all.......
but and heres the but , now i get odd characters appearing on my trip computers everytime i startup

if i disconnet the battery it comes back but the moments later the clock freezes. turn the car off then on again and all garbage apears on the screen

im guessing its the actually unit thats blown

 

That would be my guess as well, but.......

Lack of supply voltage to the trip computer has been known to cause some crazy display readings. Couldn't hurt to check/clean/tighten the connections at the back of the t/c. Would take only a few minutes.

The t/c pulls straight out from the front of the panel.

Might help?

Cheers
DD

 

Yep pulled the unit out carefully using some dental floss around the edges
and one of the connecter was partially in

tried multiple on offs with the ignition and all is well, thanks for the advice cant understand why is didnt thing of it

 

nylon wire works too if the flossing string breaks, like a nylon guitar E-string;

three places where you need a nylon guitar string so far: (I prefer the E string).

1) to pull the air intake grille under the wipers,

2) to pull the trip computer,

3) to pull the cover off the warning lights cluster between the speedo and tach.

 

Oh well i thought i had it i had only tried ignition on to "I" and all had been good, cranked the engine over and the corruption had begun, checked all the plugs and all is good but cant get rid of the corruption unless i disconnect the battery

funny this ony happed when i changed over the module, so imight put the old one back in to see if i have the same syptoms

 

Excessive voltage drop, perhaps? Any other strange symptoms when cranking, such as the speedometer needle spinning up?

On general principles clean/tighten the battery cables, main ground under the car, fenderwell ground, the two "+" posts on the firewall, and check all fuses for corrosion. Even if this doesn't solve your t/c problem (and it very well may not) it might prevent a problem next week or next month :-)




Makes sense to me :-)

Cheers
DD

 

Okies, heres my update, still having the issue i have replaced every component but still get the same symptoms ...but now a new one has popped up instead of garbled data the screen just goes blank and i can replicate it, i can also easily bring it back by popping out the fuse and putting same onew one in. "different fuses make no difference"

i have noticed with my Fan or air-con engaged when cranking it looks like the trip computer loses power and dosent come back. however if i ensure that the aircon is not engaged on start everything is sweet....until i forget to turn the fan off when cranking or if i get a longer than normal crank...


i have a Feeling that when i called RAC out to replace a dud battery that i may not have the correct cranking amps, long shot i know or could it be my alternator

only accessories that run consistently would be a GPS tracker which runs on its own power supply for days and the radio which automaticly engages on ignition

...does anybody know the required cranking amps?

 

Remove the t/c so the connector contacts are exposed. Using a voltmeter, measure the voltage on the green wire and purple wire with the key "on" and then repeat the measurements *while cranking*. Let's see how much the voltage drops.

Cheers
DD

 

Hi Guys, well i went and bought an analog multimeter cause my digital was just to difficult to read "slow"

so here goes

Accessories = radio and aircon

on with no accessories turned on i read 12v all round

Test 1
Cranking with no Accessories 11.5v-12v Cranking and Running 10.5v-12v idle

Test 2 with all accessories 11-12 Cranking and Running 9.5-12 idle

Test with all accessories and headlamps low beam 10-12v and 9.5-10 running

batterry is 4 months old and cracks 460 according to RAC

 

Not sure what you mean by "all round". Where did you check?





Dropping to 9.5 may be low enough to confuse the trip computer. Is this the voltage at the trip computer connector?

Overall the voltages look to be on the low side.

With no or few accessories you should see 13.8 or more volts when running. Since Jag didn't use high output alternators this may drop down to 12 volts or so running at idle with rear defog, lights, blowers, etc all in operation at once....and perk up if the engine speed is decreased.

Engine off, accessories off, you should see about 12.6 volts if the battery is fully charged.


I suspect you have a weak battery and/or poor connections and/or weak alternator.

Cheers
DD

 

hi Doug sorry just meant no accessories running at all, "all around"
and yes this was direct from the trip computer connecter in the final test i actually connected the unit and slid the probes down the back to get the final reading.

when i performed the test the engine was warm after a good 40 min run, so i will leave it a day or so and try again on the first start.

i just had the battery replaced and tested the charge and it looks good. i have a feeling it might be the alternator as the charge drops right down into the red at night during idle i and i don't remember ever seeing that before....any recommendations for alternators new ?

 

Hi Guys just an update, got the wifey to rev it up to 1500 as i have heard from that accurate testing should be done at the rpm,

alternator looks like it is charging sweet at 14v, but on the inside cabin on the trip feed i am getting erratic readings. 9-12