Hello fellow Jaguar enthusiasts:

My 01 XJ8 is giving me 8 MPG. Is this normal? If not, what should I check? Air filter is new, spark plugs are new, new oil change, new brake rotors and pads. I now is a V8 but 8 MPG is just hard.

Best wishes to all,


Griztkojr

 

Your mileage is off by a factor of at least two or probably three. Do you have a leak in your tank?? :-)

But more seriously, if it were running that rich you should be getting check-engine-light codes. And eventually your catalytic converters would burn out.

 

While I am sure it is possible to drive the mpg down to 8 with the go-fast pedal, mine (XK8) gets 20mpg in everyday driving and 24-25 on a highway run without stops.

 

that is awful mileage...leak in the tank maybe? do you smell gas?

 

I average 21 with long highway trips getting 25. 8 is horrendous and should be causing all kinds of issues - you have no CEL or other issues?

 

No leaks, no smell. My driving is normal. Not aggressive at all.

 

No codes or anything strange.

 

My '01 also averages well over 20.

No codes or gas smell? First check for leaks from stem to stern. Check air filter and clean throttle body. I would recommend new plugs and injector cleaning by a professional shop. A good one will give you a report on before and after specs. In my case, at about 75,000 miles these two things made a noticeable difference in economy and responsiveness. The cleaning took just a couple of days and cost about $100 plus my labor.

These things aside, 8 mpg is seriously abnormal. Are you determining that from the car's computer display or by measuring gas used vs. miles driven? Sounds like you are feeling it in the wallet so I assume you are doing the math.

 

Boomer's comments on damage to the catalytic converters should be a serious thought as they are about $1000 each.

 

May I suggest cleaning the MAF sensor, throttle body and part-load breather. Download this "how to" print it off, gather the bits and pieces to carry out the small jobs.

DiY_Document_Clean_MAFS.pdf
or
http://www.maxperformancecars.com/dm...Clean_MAFS.pdf

Once you have completed these little jobs, I would next do a hard reset. This is to "zero" the throttle body settings. A hard reset can be done by disconnecting the negative cable from the battery, and touching it to the positive terminal on the battery momentarily. This removes charge from capacitors, meaning the car's settings are reset to factory standard. Or, leave the neg cable off the battery and go and have a coffee for 20 minutes.
You will need your radio code.
Next, start the car up, it will initially have a high idle speed as the engine management system sets the now clean throttle and MAF, revs will decrease, almost to stall. Don't panic, or stop the engine, let it run it's calibration cycle.
Next is a run around to see if it's made any difference.

Report back once you have done this.

Hope this helps.

 

It looks like you are in New York. Are you in NYC traffic a lot? When people say they are getting near 20mpg in city driving, clearly they are not living in a city in the northeast with all of this traffic. The max speed I drive everyday is about 35-40mph (average about 20mph) and the rest is stop and go traffic and stop lights. I'm getting about 13-14mpg. My check engine light is one b/c my engine runs LEAN.

 

I drive my XJR with a very heavy lead foot and I still manage to get about 15 mpg

I would do what sean b said

 

I was getting 11 until I did a TB cleaning and a hard reset. (myself)

Getting much better now, though I haven't measured it yet.

 

I drive a lot of stop and go and I average about 15.1 mpg with an average speed somewhere around 20 mph. On the highway I get about 25 mpg. Check out what Sean B said. Clean everything up, reset and start from scratch. If that doesn't help, you might have a leaking injector, though I haven't heard of that occurring much on these cars.

 

i average about 23 on the highway with an 01 xj8

 

I just went through the procedure provided by Mr. B's link. I haven't been able to drive the car much but I've already seen a 5 mile per gal. increase in stop and go traffic. Not bad for an hour or so of my time.