XJ40 4.0 15L Gasoline consumption too much

I think my Forty uses too much gasoline.
I drive about 50% city and 50% country road.
rarely faster than 100kmh …
consumption 15L the trip computer says 12.3L.
Trip Computer also says that it uses less fuel overall … according to the calculator 52L in real 77Liters.

Lambda probe is new and from Bosch.
otherwise the Forty drives without problems.
class starts too …

every now and then, when I turn it off, it smells a little like fuel

are the 15L normal for 100km?

thanks .
best regards

Stojan …

15 liters for 100 km comes out to about 15.8 mpg. When the XJ40 was new it was advertised at a combined city/hiway consumption of 18 mpg.

Remember that number was under ideal conditions. Do you drive with the A/C on or with the windows rolled down. How many people are in the car. Are the tires always properly inflated. Is it flat or are there hills where you drive. A lot of variables.

With the A/C on and driving mostly around town I normally get about 16.5 mpg. Others on the forum have reported much better numbers.

My '92 routinely gets around 17 mpg with mostly city driving.

This can have quite an effect on consumption, although a later car (‘99 XJR) I was traveling back from having the front of the car repaired and was switching between having the windows open and closed, the air con was still needing refilling, I could see a difference on the trip computer as the journey progressed.
The other thing in the equation is how long are your journeys? Short ones are going to eat the fuel. When I was working my commute was <> 4 klms each way 10 mpg was about it as the car never reached operating temp. And before anybody says lazy person I needed the car at work in case I needed to follow a motorbike for his riding test.

I get 15.4l/100k in mine, city and hwy. Lots of traffic lights in town before I get to highway so lots of stop and go plus I always have aircon running - summer and winter …my tailpipes are black though, she’s always run a bit on the rich side. Oh well, the price of ownership when you drive a 4litre straight 6 …don’t really give a hoot myself.


okay then my 15 L consumption per 100km are completely normal! or?

What about the trip computer, it is possible to adjust it a little so that it comes in the direction of real

Over the years with my 4.0 1990 XJ40 I have found the trip computer somewhat inaccurate when compared to consumption calculated from a fill up to the next fill up and miles traveled. I wonder if the less efficient 10% ethanol fuel was built into the computer calculations or not. Was 10% fuel common when the cars were built? Also when mentioning fuel consumption on the forum always good to state US or UK gallons as there is quite a difference.

Litres per 100k crosses all cultural borders!

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There are so many different factors to consider when calculating fuel consumption. As already mentioned driving with the windows open, tyre pressures, number of people in car a/c in use etc but in 18 years of driving two different 4.0L xj40’s and covering a combined 80,000 miles plus, I’ve found the biggest deciding factor by far to be the length of the journey. On long trips ( say over 100 miles ) I’ve managed around 29 MPG if the traffic wasn’t too bad and I’ve been able to cruise around 70 mph for long stretches, sometimes even up to 31mpg. Shorter journeys of 50 miles or less and the consumption drops quite noticeably to around the 23/25 mpg mark. Around town with stop start type driving or a couple of weeks of journeys averaging about 15 miles and it will drop to about 15 to 17 mpg.
I’ve never noticed a fuel smell on either car following a journey of any length, that is not a normal thing for this model so I would definitely be investigating that if I was you.

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Should be. The injector cycle is adjusted by lambda, and the consumption is likely calculated from there. The cars run just as rich using more fuel. The computer knows.

UGGH :imp: thats all I can say :innocent:

What per 100 what? I dunno about that but my '94 with 193k miles is currently getting 16-17 miles per gallon (and even more SMILES per gallon) in city driving, albeit more going than stopping. This is with 91 octane ETHANOL-FREE premium petrol. It seems my fuel economy has gotten better by 1-1.5 mpg since the shop that does my service work switched from 20W50 dino oil to 10W40 full synthetic lubricant.

My computer seems to be accurate since I have checked that the real consumption is very close to the figures on the VCM. If I drive mostly highway the consumption is 9.5 l per 100 kilometers (about 29 Miles per Imperial Gallon (UK)). I use the cruise control as much as possible.

Stojan take it on a trip. No stops after filling up, constant speed say 130. Fill up again after 200km and see what the real number is.
If it is really high you may have a fuel leak, possible. Or just the trip computer. To me your 15l for mixed city and Landstraße seem pretty good…