So, I'm one that likes to shift (haven't had a manual in 10 years and I miss it), so I'm constantly shifting. When I'm coasting, a lot of the time I pop it into neutral to coast farther. A friend of mine (that doesn't know anything about Jags) says that when you lift off the throttle and the momentum of the car is moving you forward, the fuel injectors turn off, thus saving you fuel when slowing down. Is this true and does our Jags do that? Makes sense, but I've never heard anything about that before.

 

I bet you drive your friends MAD!
Read the owners manual and you will discover instant fuel mileage info...
displayed message center:
4:14 read it.

 

It's always been my understanding that with modern electronic injection systems
IF
the throttle is closed (my 1990 Merc certainly had a microswitch on the throttle linkage to pick that up)
AND
the engine rpm is above normal idle speed (say, above 1000 rpm)
THEN
the system injects no fuel.

 

I've read that section before; no reference to what happens when you let up on the gas and what happens to the fuel injectors (but then again, most people who purchase new jags aren't as **** as I am so would not be interested in that level of technology--so jag wouldn't put that in the owners manual--it may say something in the service manual but hard to find anything like that in there). Besides, the computer just says 99mpg (display limit) when I let off whether I'm in gear or not if I'm going fast enough...theoretically, if the injectors turned off, my mileage would be infinite for that period of time, not 99.

As for shifting all the time, I actually don't shift anywhere as much as I did on the '97, and that transmission is still perfect after 247k miles. Not my fault that Jag has not build a car with a proper manual transmission (why does't the XK have a manual option, or at least an auto that does proper engine-rev matching downshifting?). I'm still waiting as I am not going to go get a BMW to get a manual (been there, done that). But alas, I digress......

 

It makes sense. I'd just like to know what the parameters are on our X350s (again, that **** "I need to know what's going on, not just that it works" mental attitude.....

 

It's not unique to Jag... I'd say that all port fuel injected cars cut the fuel injector duty cycle when costing. Some also open the idle air control to prevent the "high gear overrun" engine braking you'd get on an older vehicle.

The "99 mpg" indication on the Inst. MPG is typical for most cars. Yes, technically it's infinite if the fuel injectors are cut off completely, but most drivers will have no idea what that means. Think of "99" as the equivalent of "meter pegged."

 

I recommend going to accredited tech school, if your so **** on knowing on what is going on in your car.

Enough said, as for shifting auto trans in neutral when coasting no sense, no fuel gain, if your driving a luxury car and have to worry about a few tenth of a gallon you THINK you save, I recommend you look at a different brand.

 

You could try switching the units to metric(button on the panel to left of steering wheel).In metric the engine computer calculates fuel used per 100km---so when you lift off the fuel decreases down to 0,depending on speed etc.

 

Good point. I'll check it out.

 

Gee. That was extremely beneficial. Thank you so much.....

 

That's really interesting. On my '97, when you are in torque lock up (it's most noticeable then) and let off the throttle, the car almost seems to coast without slowing for a second or so, and then you feel engine braking. I asked about it while the car was still under warranty and was told it was normal (but I don't remember the reasoning). It could be that there is a lag between when I let up and the injectors stop flowing. That certainly would explain it.

Thanks!!

 

It was zero liters per 100km whether I was coasting in neutral or coasting in gear. But I just got "Torque" so I'll see what monitoring it has. So far I really like the coolant temp readout. Lots of cool stuff to monitor, and it's bluetooth so no wires