Today we went out 'Tripping' and got through £100 of Petrol.

(Normal not complaining) Then just out of interest I looked at the average Miles per gallon on the dashboard display.

According to which I was averaging 17.7 mpg.

Most of that was on Tarmac doing about 70 mph

Does 17.7 mpg sound about right?

 

Sounds 'about right' for combination/mixed driving.

Mine would deliver 19-21mpg on the open road @ steady speed and 12-13mpg in stop-n-go city driving. Those are smaller USA gallons, mind you.

When was the last time you reset the trip computer?


Cheers
DD

 

Mine gets about 21 to 22 at 65mph with the cruise set on the open road.

 

I should have added that's on the instant setting not the average setting.

 

I have just returned from a 1,400 mile trip to the UK. Mainly motorway at 80/85 mph; but several hours in Paris traffic and London, plus crawls on UK motorway jams.

The trip computer is 10% optimistic on my car. I actually got a real 19 mpg. Aircon always on, engine driven main fan replaced by electric main fan. before the fan change it used to be 18 mpg.

So, OB, your mpg sounds about right.

Greg

 

Hi Doug

Oooops! I haven't reset the 'Tripometer' since last year!

But I do disconnect the battery every night after using the Car, so I'm 'guessing' that this would do the same as a reset?

 

Hi JT

I've never used 'Cruise' on this Car, I'll have to try it.

 

Hi Greg

Thanks

Hope you enjoyed your Trip to dear old 'Blighty'

No wonder these Cars aren't more popular with that sort of MPG but we're getting some nice hot Weather at last, which probably won't be with us very long.

So got to make the most of it while its here.

 

When we had the Red Terror, it was like Greg's, as in 10% out on average at the dash unit as compared to actual fill and read.

Mostly it sits on 15L/100km around the 'burbs. We have 50KPH limits in the 'burbs, so the V12 is not so happy, and 110KPH on the open road, as in interstate highways etc, so again the V12 is not real warm and fuzzy.

On our "Round Australia" cruises, we averaged 11.2L/100kms for the whole trip, which was 20,000 odd kms each time.

Also, please bear in mind, that my engine was rebuilt by me, and fully balanced. The engine also has NO emission junk at all, NO balance pipe, NO AAV, 70mm throttle discs, 16CU ECU, foam airfilters, cold air intakes, mechanical FPR set at 31.5psi. Both camshafts were dialed in "1 tooth" on the micro wheel in the "advance" mode. The a/c compressor is the new generation compact syle, which has less drag than the Dinosaur unit. It also has twin themo fans. The exhaust is 2" ALL the way to the tips, with minimal mufflers at the rear. NOT noisy, just "throaty", and "Growls" when stood on. We do NOT have Cats in that year model.

I have NO idea what, if any of this, has to do with fuel economy, but it is better than it was pre the work, and it goes like stink just for fun. Redline comes up REAL QUICK.

 

Wow Grant!

You're making me envious, how much is a Gallon of Gas in OZ?

Even though the Summers that we have in the UK, can be measured in just a matter of weeks.

She still costs as much in Petrol to run as the price some people pay for a good used Car!

So you either learn to live with that, or go and buy something else.

If you think that 50 KPH is bad, then you better stop reading now, as in certain places in the UK the limit is 20 MPH!

'Warm and Fuzzy'-Not!

 

Now its $1.50/litre for the standard 91 Ron. I only use the 98 Ron which is $1.65.

Back then it was under a a dollar mostly for the 98.

I have always been of the manner that it costs what it costs.

Mind you a V12 now would be stretching the purse a tad, so the V6 reigns supreme. It sits on 10.1L/100 aound the burbs, and 8.2 on trips, and never a thought of what is hanging by a thread awaiting to bite when least expected. Not that the V12's ever did, but in my mind, common sense must prevail, and age is age, and there is only so much that can be done within the preventative scheme of things.

Add to that the aching bones, rife arthritis, one leg, etc and the S Type maintenance simply makes sense to me.

We were seriously tempted by a 1990 Conv the other day, but resisted.

 

Cheers Grant

Very wise words from the WoOZ, it costs what it costs and I'm just getting used to that now.

 

OB,

I like figures (rather than actually care about my fuel consumption!) so have kept a log of every tank of fuel that's gone into my XJS over the last 12 years. As a result I have detailed comparisons of the accuracy of the fuel consumption calculation of the trip computer vs the actual consumption.

It may be that the electronic sensors of the AJ16 engine are much more accurate than the earlier V12s. However, over 12 years, my trip computer fuel consumption has been optimistic by only 2.82% compared to the actual consumption, which I think is pretty impressive.

By comparison the trip computer in my 2004 x350 XJ8 has been optimistic by 4.96% over the last 60,000 miles.

Does any of this matter? Not really, but I'd still like to really understand how the XJS measures the fuel used?!

Paul

 

Paul
This must qualify you as the Jaguar Enthusiast's Enthusiast. The V12 measures the injectors' pulses and their duration, somehow, and converts these into the fuel quantity used. On my car's trip computer, the mileage part is dead accurate, but the fuel used under-reads by 10%, thereby giving an optimistic MPG. Quite honestly, given the elderly nature of the ECU chips and circuitry, and the inherently inaccurate pulse length to fuel squirted in calc the ECU makes, I am not surprised about the 10%.

Greg

 

Greg,

Perhaps "saddest Jaguar enthusiast" might be more accurate! Tks for the info. I'm also surprised then that it can get to within even 10% of accuracy. Do you know if it measures it off a specific injector, or does it do it from the defined pulse duration setting of the ecu (irrespective of what the injectors might actually do)? Just musing: I wonder if it reads optimistically if that means that the injectors are really staying open for fractionally longer than they are being told to by the ecu?

By way of nothing relevant, I had some Rover SD1s in the 80s and they had a "fuel-flow sensor" mounted somewhere near the fuel rail which provided the signal for the trip computer. I had the tiniest leak on the sensor on one car and it gave weird consumption figure readouts.

Paul

 

Funny you should say that Paul, I was also wondering how that worked.

 

Thanks for that Greg, now I know!

I also started keeping records of every time I filled up and how much it cost but when I started adding it up, I wanted to slash my own wrists!

So I'd rather bury my head in the Sand and just hand over the plastic.

 

What I found coz I was bored one day, and the JD was out, and I was a LOT younger.

That "Black Box" in the boot, alongside the 2 well discussed relays, is the interface for the trip computer fuel deciphering. Mine even had "V12" on a sticker attached.

As you ALL should/do know, teh injectors are fired in 4 banks of 3.

This jigger takes the pulse reading from the 6B section and does its smoke and mirrors, to give the numbers we luv so much.

The mileage, distance etc is direct from the transmission transducer. That Yellow wire splices off just near the LH footwell vent, and also does the pulse for the Cruise Control. Busy little item that Transducer?.

Gregs 10% is about the mark that I have found on most that bother to read that screen for the fuel side.

The accuracy of the rest of the info I also have found to be "spot on".

Side note:

Our 2 S Types are spot on with the fuel usage as compared to actual fill and calcualate. Now please remember that down here this "Spot on" may be a stubbie or 2 out, depending on the temp of the beer, and the number of meat pies comsumed whilst filling the tank.

Again, "It costs what is costs", and they are all better than the Mighty MK7 I once charioted around in, man that thing could DRINK the fuel.

 

Paul,
Grant has explained in more detail. But the trip defintely measures actual pulse length, not a set average. One of the great games we play in the V12 is an absolute flat out acceleration run from a standing start with the trip computer set to "instant".

I have had it down to 3 MPG once, and 4 MPG is easy to get!

There is no fuel pressure input to the ECU's calculation, so that is also a (real) variable that is not actually measured by the system, and may well account for the 10%. Also, whisper it only, Jaguar were not above setting up such a system on the optimistic side to give the owner a warm fuzzy feeling!.
Greg

 

HA, I did the 3MPG also, what a HOOT.

Jaguar fudguing the figures, NEVER, they all do it, still today, and the owners "warm and fuzzies" is important, as it always has been.

Increase the tyre pressures to MAX, Alternator unplugged, etc etc, are common theories as to how they got the figures they got, that we find unachievable.