Trip Computer Readings & Fuel Consumption

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Trip Computer Readings & Fuel Consumption

Postby ptjs1 » Thu Dec 04, 2008 11:43 pm

I've got what seems to be a problem on my recently acquired 97 4.0 Sovereign LWB.

I've just bought the car this week and am on the first tank of fuel. However on my 250 mile trip today, I noticed what I think are strange readings on the trip computer. The instantaneous fuel consumption seems to vary more than I would expect under constant conditions. For example when driving on the flat on gentle throttle at 60 mph, it constantly changes every couple of seconds eg 28.2, 23.2, 34.3, 28.2, 21.4. When going down gentle incline on motorway under trailing throttle, it shows 69.2, 92.1, 69.2, 21.4, 54.2, 69.2

I haven't put another tankful in to check the actual consumption, but the average fuel consumption is showing 23.2 over 250 miles, a mix of 65mph motorway, 80 mph motorway and 30 miles of urban.

My AJ16 XJS shows far more constancy on the trip computer under similar conditions. A constant incline of road with constant throttle opening and the instantaneous fuel consumption stays within 1-2 mpg.

So have I got a schizophrenic instantaneous function on the trip computer (where is the fuel flow sensor?) or do all XJ8s do this? It just seems strange that my XJS is so much more constant. Also what mpg do people get? Is a motorway-biased average of 23mpg about right or poor? The previous owners last 2600 miles indicate 20.7 at average speed of 49mph which speed would imply nearly all motorway use.

I don't really care what mpg it does, I just want it to do what it's supposed to do!

Any thoughts?



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fuel consuption

Postby joejag308 » Fri Dec 05, 2008 12:13 am

Paul the readings on the trip computer are very active and its the same with the average MPG on a longish run if you zero the trip computer and go directly on a motorway the average i get is about 24-26 mpg if i have to do mileage before going on the motroway it does take a long way to get the 24-26 average back up, if at all.
I had an XJ40 for 9 years and had the similar readings you have with the XJS so it looks lke the different individual instruments work in a different way......its called progress so they say.......Joe.... :lol:

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