Fuel Computer Problems

Following comments re:- Fuel Computer Problems under the Fuel Consumption topic, I think we should continue this subject under a new topic heading, so as not to distract from the one we could be accused of hijacking as it may take a bit of time
When you are ready Clive and cheslynjay we will carry on here if that is OK with you.
John

I'll join in with this one and get some advice from you as well John. My trip computer flashes all the time. Diagnostic mode? I get a petrol level reading and an MPH reading that seems to be some sort of average. I don't get an MPG figure. I've always assumed that the fuel flow meter is the most likely suspect and have made a couple of attempts to find a cheap spare to try but no luck so far.

Am I working along the right lines?

Cheers

Thanks John,will try this weekend and let you know.
Some points: I do keep disconecting the battery while car not in use
Speedo only works intermitently
Just incase these have some bearing on the issue.

[quote="scottydog"] I get a petrol level reading and an MPH reading that seems to be some sort of average. I don't get an MPG figure. I've always assumed that the fuel flow meter is the most likely suspect [quote]
Hi scottydog.
In my experience if the fuel flow unit, or connections to it are at fault, but you get an average MPH reading, the computer will read 99.9 in MPG mode. As the computer will see pulses from the speed sensor, therefore milage, but it sees no fuel being used, hence an extremely high MPG reading, however the max the display can show is 99.9. This is why I have asked the others for the reading of the MPG. This is an easier check than putting the unit into diagnostic mode. What I would do is whilst driving, put the computer into MPG mode, push the reset button, (you may have to select MPG mode after pushing the reset button) and if the fuel flow unit is not sending pulses to the computer, after 440 yds, a figure will appear, and climb steadily upwards to 99.9, and stick. Now if after 440 yds the display shows 0, the computer sees car using fuel, but no pulses are being detected from the speed sensor, therefore no milage, hence zero MPG.. If however having pushed the reset button, the dashes which appear stay as dashes, and neither change to 0, or 99.9, then no pulses are being detected by the computer from the speed sensor, or the fuel flow unit. I would then suspect bad contacts behind the instrument cluster. Which is why I have suggested to cheslynjay to clean all his connectors in the first instant, as in his case until you can always select MPG every time you want to, then no other checks can be made.
Hope this helps, however although it makes sense to me, I might not have put it in a way that is clear to someone else, therefore do not hesitate to come back with anything which is not clear.
John

I do keep disconecting the battery while car not in use
Speedo only works intermitently
.

HI cheslynjay
If you disconnent the battery, like I always do, then yes, the display will always come on with 8888, so you do have to press the reset button each time you reconnect the battery.
With regard to the speedo, this tends to prove that you have many poor connections behind the instrument cluster, and a dismantle job and clean contacts MAY just be your problem. Let us know how you get on.
John

Hi John,

I did as you suggested and put my computer into mpg mode, it was showing 99.9. I then reset it, it now showed dashes, and went for a drive. After a short distance the dashes suddenly changed to 99.9 again and it stuck on that.

Clive

Hi John,

I did as you suggested and put my computer into mpg mode, it was showing 99.9. I then reset it, it now showed dashes, and went for a drive. After a short distance the dashes suddenly changed to 99.9 again and it stuck on that.

Clive

Well done Clive. Clearly the problem is with the fuel flow unit either not producing pulses, or bad connection along the loom to the computer.
The first thing I would do is to disconnect the three pin connector on the side if the fuel flow unit, spray contacts with a switch cleaner, and connect and disconnect a few times, this has the effect of cleaning the pins/sockets of surface corrosion, and then try again. I did have problems with this connector many years ago, and a good clean cured the fault. However dont get too excited yet, I can think of a few other faults that will give this indication. but first things first Let us know how it goes.

John

John - I get the 99.9 mpg figure and dashes instead of the fuel remaining figure.

John - I get the 99.9 mpg figure and dashes instead of the fuel remaining figure.

Hi scottydog.
It looks as if you have two faults here.
I dont know if you have done a computer reset, but that would be worth a try for your "fuel remaining figure" I assume that means the top LH fuel in tank figure, AKA fuel gauge? To do a reset:- Disconnect battery, press and hold reset button at the bottom of the RH instrument (Rev counter) for 15 secs, release, reconnect battery, press reset button again, momentarily and let me know what happens.
With regard to the 99.9mpg reading, do the same as I have suggested to Clive. Just one note of caution, for Clive to, do not be tempted to use any form of abrasive paper or cleaner, when cleaning pins/sockets, as this will remove the plating on the surfaces, not a good idea, just a spray contact cleaner will surffice.
John

Hi John
Have not had chance to try your solution as was at "cars in the park" Saturday and the wife stopped me playing with the car on Sunday.
You look busy with the other problem computers at moment,I shall be on holiday Thursday but if its okay with you would like to resume when i get back and hopefully the other guys will be sorted.

Thanks Jay

Hi John
Have not had chance to try your solution as was at "cars in the park" Saturday and the wife stopped me playing with the car on Sunday.
You look busy with the other problem computers at moment,I shall be on holiday Thursday but if its okay with you would like to resume when i get back and hopefully the other guys will be sorted.

Thanks Jay

Hi Jay
No problem, Have a good Holiday, hear from you when you get back.
John