just checking in
 

My ,94 XJ limited just turned 455,000 KM today still going strong

i would do heaps more if the fuel economy around town wasn't so bad hahahah

The funny thing is that with fuel prices having been so high, I have been using the 4.0L XJ because I would prefer to use ULP91 (it is much cheeper, rather than 98 in the 3.6L Pentastar JKU).

I usually give the XJ, ULP95, but the price of that lately has been ridiculous.

The XJ is now at 390,000km and I have just noticed a craick in the (original since 1995) air intake manifold.

What fuel "economy" do youse get in your 4.0 ?

Mine is mainly about town, short trips, and I fill up ~60L per ~360km
which equates to about 17L per 100km

If I do longer trips, I get about 400km per 60L

My trips are usually long and I have to refuel at 420+ km at a time.

In city and country driving, our figures are probably spot on. City driving gets me 360-380km.

Strange thing is, fuel economy hasn't worsened with the age of the car - 1995 sport.

Fuel economy could depend on a lot of things.

e.g. drive on the Barrier Highway at night, and you will struggle to do Broken Hill to Cobar on a single tank. This is due to the frequent braking for the roos.

During the day, a tank will get you across without a refuel. I have also found that ULP91 gives greater endurance than ULP95. Strange but it's true, at least in my case.

To the best of my knowledge regarding theory of IC engines;

If an engines parameters specify it will run on 91 (which it does with an XJ), then it is theoretically impossible to gain any benefit from running fuel with just higher octane rating

Some bedtime reading for you :)

Secondary but related question...have you ever noticed your engine pinging?

I had this, and my plugs were white, changed them out for the same Champion 12RYC, still some pinging, gave it several Italian tuneups, and it seems cured, so likely carbon from short runs

I dont like the burned white plugs though

crazy thing ive noticed (for years) that if you drive for economy they seem to tune themselves accordingly.

by that ive noticed that if i tow a trailer or use the A/C at first the car seems to struggle a bit, but after a little while it gets its act together and runs well

even to the point of starting quicker and idling better. however the gains are then lost if i drive without A/C or trailer, its like the car detunes itself.

i think you need to drive it like you stole it regularly

and there's the problem the fuel economy then sucks

hehe, what are those italian tuneups- water into the TB intake?