I tried to search the forum for this, but could not find any good answers..

My 98 Jaguar XJR Supercharged uses 1,8 litres of gasoline per 10 km. (I live in Norway, so that is our measure.) I feel that is too much. Is it?
If so, what should I check to figure out what the problem is?
Thanks in advance for any help.

Kenneth

 

MPG : 16 city / 21 highway

 

Thanks. My car only gives me 13,1 MPG with mixed driving. (City and highway) So it actually use too much gasoline. Any suggestions on what to check?

 

Correct tire pressure,use premium fuel & ensure your gas cap is sealing.

 

If you can, have a look at your long term fuel trims.
Your ecu may be adding lots of fuel to compensate for a dirty MAF or an air leak and wont set a code until it adds 25%
If not already done try a new air filter, clean the MAF, and try some BG44K fuel injector and engine cleaner (or something similar)

 

All of the above, plus a new fuel filter and new spark plugs and slow down. It is so much fun to open it up . . .

 

Thank you. I will check the MAF!

 

Check the cam cover vent tube for obstruction and for excess oil in the air tube/TB downdraft. The fuel filter is a simple and maintenance replacement if it hasn't been done in awhile along with spark plugs. When plugs wear, they gap out...they may run fine, but you will notice lack of power and loss of fuel mileage. (Ya beat me to it Jim...lol)

25.7 km City/33.8 km Hwy ....so yeah, your drinking a big cup of fuel at 21 km. Of course that can be determined by driving habits also...I have an issue with a heavy foot, so I just watch the fuel gauge...lol.

 

I drive like a priest
Thanks. I will go straight down to the garage and start checking!

 

I'm actually ordained not sure I buy that one, from experience lol.

 

 

Hi Kenneth,

In addition to the above, very common causes of reduced fuel economy are a stuck-open coolant thermostat that prevents the engine from reaching full operating temperature, or a problem with the engine coolant temperature sensor (ECTS) that tells the engine control module (ECM) that the coolant is cold even after the engine has reached full operating temp. Both issues can cause the ECM to continue to apply cold-start fuel enrichment continuously, even when the engine is hot, causing rich running and excessive fuel consumption.

Please keep us informed!

Cheers,

Don

 

Once you've cleaned the maf, I think you need to do a reset by disconnecting the battery.

I've had similar issues recently, tried doing a cat clean with that mannol stuff and it seems to have helped.

My issue is oil dropping into the cylinders through the valve seals. I've used a handy dandy mini USB borescope camera to look inside and the cylinders are a bit coked up. Catch twenty two situation though because that stuff can head into your cat once you clean it out.
If that happens now, I put acetone into the tank or preferably, spray acetone into the air intake, as it does unblock the cat.

Need to sort out the source of the problem really otherwise you'll keep having to repeat this.

 

I started with the spark plugs and took out the four from the left side. Two of them had what seemed like new oil around top insulator. My guess is that someone spilled oil when filling and it went dont down there, because the thread and electrode part wasn't oily. I cleaned them and put them back.
The motor runs a little smoother now, so I am going to get new spark plugs, because the car obviously need that. I think the NGK 2341 is ok right?
The spark plugs in the car now is Bosch FR70C btw.

 

Hi Kenneth,

A common cause of oil on the spark plugs is leaking spark plug tube seals, which are part of the camshaft cover gasket set.

I think you're correct about the spark plug. I'm on the wrong computer to check the Jaguar Vehicle Specification booklet, but according to the NGK parts finder, the actual OE spark plug for your engine is 2341 / PFR6G-13E.

NGK Parts Finder

Cheers,

Don

 

My plan now is to wait for the new spark plugs, clean the MAF and at replace the air filter, and fuel filter at the same time. Then check if oil is still dripping onto the spark plugs that were oily. If so, replace the camshaft cover gasket. Sounds like a plan or am I missing something?
And thank you so much for helping me everyone!

 

Mine's been getting around 13mpg according to the onboard computer, while driving to work and back mostly (lots of stop and go, 0-50-0 mph, etc). I think I've got around 19mpg when doing mostly highway driving before, haven't been doing highway nearly as much as I'd like to. Got a day trip planned in a couple days where I'll be able to put about 500mi of highway on the car and see how it goes. Have done plugs, fuel filter, maf clean, PLB clean, air filter. Been suspecting a slight leak somewhere though that I can't trace, or haven't tried hard enough, my ltft usually hover around +7% idle. Injector cleaner is the next step.

One oddball one I noticed recently, may or may not apply to you - the coupling between the MAF and intake tube was slightly loose, causing the intake to pull away from the MAF bracket a bit under high engine load and let in some unmetered air. Caused a bit of stumbling and momentary loss of power under heavy acceleration. If the basics don't solve the issue it's worth checking for air leaks, things like the full load and part load breathers crack easily, and there's lots of hoses behind the intake to leak as well.

 

Have you checked to see if your thermostat is stuck open? Have you inspected the coolant temperature sensor wiring and connector for any signs of damage and measured the resistance across the sensor terminals when the engine is cold and again when it is hot? Pretty easy tests and very common causes of rich running/poor economy.

 

The motor gets warm really quick (the heating start almost immediately) Cold start with the coolant cap off show no circulation. Are there other ways of testing if the termostat is stuck open?
The cololant temp sensor wiring and connector looks good, but I haven't measured the resistance across the sensor terminals. I don't understand how to do that.

 

For this, I'd simply replace the thermostat, its probably due and its cheap. I may also be tempted to check/replace the water pump? If its the original with plastic impellers, it may warrant your attention if its not performing. Its a bit of a bear to get to on the XJR, but quite doable with patience.