Hi All,

First post here as i've only owned this jag for a week. The mileage i'm getting is appalling, far below that which is mentioned on several websites. (may just need a tune) around 5km per litre or 13.5 mpg

My question is, has anyone known of or have had any experience in replacing the V6 engine for something smaller? Please save the "if you wanted an economic car you should have bought a honda fit" bs thanks.

I'm only interested to know if its possible or not, if it has been done, what engine fit with the least modifications required etc.

Thanks in advance

Matt

 

Which V6 is your S-type equipped with...? My 3.0 gets roughly 7.6 km/l in mixed driving with a modest amount of expressway driving included. This increases to 10.6 on a straight highway run at 70 mph or 113 kph.

How many km are on the car and do you know its service history? Tune ups tend to be expansive as the manifolding must be removed to access the RH cylinder bank (#s 1,3 and 5); it is often prudent to replace the plugs, coil-packs and valve cover gaskets while the manifolding is removed.

 

Hiya Matt, and welcome. In the kindest, gentlest manner I can muster, your statement above probably isn’t going to win you too many friends. Not exactly putting your best foot forward, but enough of that.

Swapping a different engine into an S-Type would be an incredibly daunting task. The security system will immobilize the car if it can’t talk to the stock ECU. Even if you went with a non-electronic control system for the donor engine, the security system won’t be happy. You’d have to trick it into seeing what it wants to see. No idea how that could be done.

I only know of one project on this forum like you are thinking. No idea how it ever turned out. I think it was one of those interesting threads that just faded off into the sunset, never resolved.

Your present fuel economy sounds horrible. My ‘02 V6 regularly gets about 25 MPG, plenty of power, etc. Are you curious to figure why your car is using so much fuel? Diagnosing and repairing what you have is going to be way easier than an engine swap, but you said you weren’t interested.

 

Thanks for your reply and the useful information, I believe the engine type is AJ30 if thats correct, havent driven it since due to the fact it would cost me $45 nzd every 100km.
I haven't received all the service history just yet, I had some in initial reports over the phone (It had to be shipped to my city from elsewhere) which all sounded positive but it has done 128,800 km or there abouts.

It really does seem to be in great shape.. but something is definitely off.

 

Hey Karl, thanks for your informative reply and yes you're quite right maybe i'm talking to a very different audience on this forum as opposed to previous encounters.

I will of course attempt to get to the bottom of whats causing my Jag to lag, but in the meantime I was curious about downsizing. Any further information I find from the dealer or mechanic I will post on here

 

umm — in this case , a down size of engine will be just as hard to achieve as an engine up size .
and although a few have managed this successfully. Many have tried and failed . As Karl said there is far to much electronic wizardry going on in the S-type to hinder this swap ether way .
but I will put it out there that if you were going to swap the engine you might as well go bigger ,
because my 03 supercharged 4.2 v8 S-type does 26mpg . So I doubt very much your issue has anything to do with your engine size .

i would start with checking the engine is reaching the correct running temp .via obd2
then check the MAF sensor readings via OBD2 also .
The MAF generally fails without a trouble code and tends to cause rich running conditions when they fail .

 

How much have you driven the car in the short time you’ve owned it? Have you manually checked the fuel consumption, comparing fuel used versus distance driven? Or are you just going by the computed value shown on the dash display?

The reason I ask is because the computed value may be incorrect. The computer has no way to know how much fuel is actually being consumed. There’s no flow meter keeping track. The fuel economy display is based on an inferred consumption value of what the computer thinks is happening.

I haven’t found any supporting documentation, but my theory is the computer keeps track of fuel consumption based on injector duty cycle and fuel pressure. At a certain duty cycle at X pressure, that should translate to a precalculated consumption rate.

However, certain factors can skew the results. For example, Injector rail pressure is controlled by pump duty cycle getting feedback from a fuel pressure sensor. This sensor could read high and cause the actual pressure to be low. Low pressure reduces the injector flow, but the computer doesn’t realize this. All it sees is a lean condition (per the O2 sensors), so it ramps up the injector duty cycle to compensate. The computer mistakenly displays this as higher than normal fuel consumption, when it may actually be close to normal.

Have you checked the long term fuel trims? Such a condition as described above would drive the trims high. There may be other scenarios that could cause a similar erroneous mileage display. Are you getting any OBD fault codes?

 

Downsizing is going to cost a HUGE amount more than keeping the car AND buying an extra one. Not viable financially, not even vaguely.

If you're really not interested in trying to find whether your car actually has a problem (as it at first sight appears, but based on very little information) then all you can do is move the car on.

However, if you're willing to let people help then at least you should find out whether it's the car, not the car, something you're doing, or what.

For example, like all modern petrol cars, your car should run CL (closed loop) but suppose it isn't - you'd get poor MPG.

Easily checked with a cheap OBD tool.

Also, if running CL it should have fuel trims within about 5 of zero - same tool needed.

May to some sound like rocket science but it's not.

 

[QUOTE=Datsports;2192285
i would start with checking the engine is reaching the correct running temp .via obd2
then check the MAF sensor readings via OBD2 also .
The MAF generally fails without a trouble code and tends to cause rich running conditions when they fail .[/QUOTE]

Thanks for the advice i'll look into this

 

Appreciate the information here Karl,

I've only driven it 62.7km. I topped it up with 34L of 95 octane. Gauge went from halfway to exactly 2/5 which is roughly 13.6L of fuel used.

62.7 km / 13.6 L = 4.61 km/L which is around about the figures the dashboard displays. Even on motorway cruising at 100 kmh it never exceeded 5km/L.

Thanks for your advice and I will look into what you've mentioned.

 

You have a six speed gearbox, which should result in lower RPM at highway speed than my 5 speed automatic. Does it FEEL like your engine is working harder with higher RPM than what would appear normal? Also, does the cabin have a fuel smell? When my fuel pumps (yes, we have 2) were beginning to go, my MPG on the same drives dropped by 3, before the fuel smell was noticeable. As KR mentioned above, fuel trims out of whack could have you dumping more fuel in than needed (rich) that you could detect at the exhaust with just your nose.

And, a code reader is a must to keep you from chasing your tail. Good luck!

 

That is perhaps the problem as it could easily mean you have far too little and imprecise data.

 

One other thing to consider is that given the shape of the fuel tank, the fuel gauge on my car seems to indicate higher consumption when the tank is below half full. The only way to accurately (or semi accurately) check your mileage is to fill the tank and on re-fill divide the fuel added by distance traveled. Checking the car for error codes and fuel trims is a good first step.

 

Another point to consider - if car sat it may have old gas in it. This in turn will degrade octane rating and may result in loss of efficiency due pulled timing. I would only measure gas mileage on a car that I personally filled with fresh gas.

There are couple things you could do to marginally improve fuel efficiency on a high-mileage car. They are:

a. Make sure your spark plug are not fouled
b. Make sure your injectors work well and do not leak or drip, you can start by running quality fuel injection cleaner with your next fill.
c. Select tires designed for improving fuel economy - they tend to be harder and louder, but will give you extra mileage
d. Change differential fluid and use synthetic fluid to refill - this will give you marginal boost
e. Inspect brakes, inspect parking brake - if calipers do not fully disengage it will reduce your mileage.

 

I would suggest resetting your trip meter when you fill the tank...

Drive the vehicle until it gets to the 1/2 reading. Refill and do the math.

I know my STR drops to the middle of the gauge much much quicker than it drops to the 1/4 mark.

 

The only way to reduce consumption in your car, realistically is to throw a Diesel engine in it. And I doubt you can do it as well as Jaguar did.
So I know you asked not to be told what to do, but let me tell you in any case, you are barking up the wrong tree.
I have a 3 liter, and it is actually economical for the power it produces, manual and a delight to drive. Downsizing an engine will not necessarily give better fuel economy, just give you a car which will be neither fish nor fowl.
In other words a stupid idea. Find a Diesel engined S if that really is your main concern.
Otherwise there is plenty of economy to be had by just getting your present engine sorted. It is not an inefficient engine at all, I think it is one of the best 6 cylinder engines you could buy in its day!
Sort your car out, it will be worth it. If you can do it yourself, it might actually not be that expensive. If you can't, learn, or buy another car if you can't afford to send it out. Garage charges at Jag are not be cheap.

 

.

 

Interesting point! And actually I haven't topped it up over half way simply due to the price of fuel in Auckland. ($1.51 USD per litre).
It would cost roughly $75 USD for a full tank. or more importantly due to exchange rate: NZ $120

 

I think I will take into Jaguar Auckland for a thorough service. If they find anything unusual i'll put up here on the thread.

 

Thanks for the suggestion, I will give this a go