Hi everyone, here's the deal- my jag (1998 4 l. with 240.000km on odomether) takes 26l / 100km. that is alot! my CO is 7,5 and the allowable is max 3.0.. i've tryed to connect the car to computer (not dealers, the one that fits most cars) result was: no mistakes... now your opinions would be appreciated.. where should i look? oxygen sensors? catalytic converters? ignition coils (perhaps anyone knows how to chek them with tester or..?) ... what else could couse the problem? oil is fresh, air and oil filters changed, tensioners,rails and chains are new, car starts and drives fine (sometimes feels slight vibration on idle), no warning or check engine lights on....

 

At 240,000 km, (150,000 mi) the first thing I would check is compression.

Has mileage (currently around 9 miles per gallon - half of normal) degraded slowly or has this occurred only recently?

 

it came up more suddenly than gradually, i've noticed that onboard computer displays 26,6 l / 100km, (don't look at that to often), with 10 liters of gasoline i can drive aprox. 35 to 40 km.

 

I had the same problem on my XJ8.

Turned out to be the oxgyne sensor on the exhaust down pipe.

your car will have two, but the one on the exhaust mainfold side is one that goes first. Cat have a good life cycle, but if you are getting a rattel at the point near the drivers door then the inner plates could have collasped.

My bet is the sensor. They cost around £50 in the uk. Your dealer should be able to check with a Voltage test, as the sensor is a eletronic gate which allow the correct mixture of air and fuel.

 

I hope that it's sensor or something exept compression, the strange thing is that the cpu (i've had connected) showed nothing, although that cpu was somehow hard to sinchronise with the car (so I dont believe it to much), I guess i have to check those, and compression, just to be shure....
perhaps you know about those sensors that go after the catalytic converter? can they make influence to? or main things are upper ones?

Thanks for info guys.

 

I would do the Oxygen sensor check first. You can do the basic test your self with a Voltmeter. If the sensor is working then you should see the circuit opening and closing this is indicted by a drop and increase in the volts. I would also check the condition of the wiring.
The exhaust sensor is mounted a the top of the down pipe. This is on the right hand side in the Uk as look from the front of the car. You will need to remove the covering to get a good view.
The major problem with doing the test at home is that the exhaust system get very very hot very quickly therefore the chances of hand burns are very high. Best to take to a dealer as they have the software to scan the problem. There is also a very go link on the web, just type in lambda sensors that will describe the test.

 

Just a quick word of advice, if you're going to use a volt meter use a high impedance kind (not analogue). Also the O2 sensor actually generate electricity so if you connect a volt meter to it you should get a fluctuation from below .5 volts to above .5 volts as the cat warms up. Better if you have a diagnostic tool (OBD scanner) connect to it, you can see the response better. If you are on idle and rev it up you should see a quick voltage change and again when you release the throttle, if you don't this O2 is getting "lazy" and should be replaced. Normally it should be checked once every 50k miles and replaced at 100k. Most of the time they don't go bad but they get lazy, that's why the mileage drops and you don't get a code out of the scanner and the Check Engine light doesn't come on.

Alan.

 

The detial from Icebreaker is very good, i am sure if you follow this i am sure you will fix the problem.

 

Thanks people that's a good knews so far

 

Thanks for your ditto, Thejagman!

Alan.