i understand that, but that still is requiring fuel to keep an idle, i'm talking about down hill coasting while having to keep a specific speed. talking about using less fuel period, and when engine braking, you're in fuel cut off mode which uses NO fuel period where as neutral requires fuel to keep an idle...

 

WTF??

That made no sense whatsoever. Maybe you should try English next time . . . .

 

nevermind i even said anything...

you just don't understand what FUEL CUT MODE is during engine braking and how NO FUEL IS USED when engine braking because of the FUEL CUT...

negative influencing force to the engine = forces that the engine sees that isn't generated by the engine, sort of like vacuum and positive pressure... positive pressure being what the engine it's self is generating and vacuum being the negative force that is making the engine spin the same direction more then what the work of the engine is putting out thus causing a negative force.

maybe you should try sinking your nose further into mechanics...

PS, i'm done, i have no need to argue with those who don't want to learn.

 

Quick clarification needed on the fuel cut off during engine braking please...

Nobody has spoken of a quoted source that told them engine braking = fuel cut off mode. Does everyone know this because of their scan gauge? Does the scan gauge measure injector duty or throttle position?

There doesn't seem to be any clear info on here as to why or how the engine is cutting fuel. I am not arguing that is doesn't. It makes complete sense and if everyone is getting a null readout on their gauge under engine braking that further verifies this concept. However... This data is coming from where? How is the scan gauge actually measuring fuel and injector duty?

EDIT: I have recently read that DFCO (deceleration fuel cut off) is responsible for this increase in mileage while engine braking... Is there a confirmed source that the 1st gen xB has DFCO?

 

That's a very good question. My experience with my '06 xB with a scan gauge suggests it doesn't. I have a large long hill that I go down on a regular basis coming into town and I've experimented a bit with leaving it in top gear vs snicking it into neutral at the top of the hill. I find I get higher mileage indicated on my scan gauge going down the hill in neutral. Plus, I'm going faster at the bottom (in fact, fast enough to maybe earn me a ticket if I keep doing it ;^).

I've read others here who've said there is a fuel cutoff. Perhaps it's a stick vs auto thing?

 

Wow.

Pot, meet kettle.

 

this thread turned from "educational" into an english lesson...Ok, so I have an auto tranny, does any of this engine braking vs. coasting in neutral have anything to do with autos?

 

my .02

Having a vehicle go from drive to neutral( say while going downhill, to possibly gain some more mpg's) , then back into drive once back on the flat has got to also put some strain on the tranny , no??

I have a 5spd. When ever I go down a steep enough grade, I keep it in gear(say 5th), maintaining 55-60 mph , fuel cut off is in effect, since I'm close to 3K rpm's (thus above the 1700 rpm cut off mark). Even at the bottom of the grade, I'm going 55 mph while in gear (not to mention I have much better control of my vehicle in gear- safer all around position).

The engine braking senerio has its place. I tend to utilize it , say I'm in 4th gear going 35 mph aproaching a stop light- nearing the stop light its still RED, and as I get closer I'll down shift into 2nd gear(say going 25 mph)- RPM's kick up to about 2300 RPM's (still fuel cut off) , the light turns GREEN- and I coast up to the light still in 2nd but also ready to jocky for position to get into the flow of traffic fairly quickly (and get through the gears at least to 4th to optimize mpg).

I'll also occationally downshift from 4th or 5th coming off a offramp going say 55mph , I'll start out foot braking getting the car down to 30-35 mph then I'll down-shift to 2nd gear to help the car stop a bit quicker, yet not putting a significant load on the tranny (ie. not going 60 mph in 4th , then slamming it down into 2nd gear while still going 55-60 mph .... thats a NO-NO )

Does any of this info. register to anyone hear reading? I've done my best to put everything in laymen terms.

 

I have limited experience driving autos. However, you can go from drive, into neutral, then back into drive , but there isn't any ability of changing of gears at different rates of speed (onboard computer controls all of that for you, I mean come on.. thats why you bought an auto- to take the guess work on when the proper time it is to shift, and the apparent hassle that comes with sticking your leg in to engage the clutch).

If I had a auto(would mainly only work with 4cylinder cars/trucks), while above 1700 rpm's taking your foot off the accelerator will at least not give the engine any gas- while coasting into something, going downhill, etc. That saves some gas right there.

 

This fuel cut mode confuses me, people say that when you leave your car in gear and just coast the fuel used is zero. If I were to turn my ignition off while going in a straight line and leave it in 5th gear it would also use zero fuel, but the car would stop real quick. Please explain how using zero fuel with the ignition on and then off makes such a big difference.

 

re-read my first post above.
When your above 1700 rpm's , in any gear , then take your foot off the accelerator- the fuel injectors STOP giving gas to the cylinders so the spark-plugs cannot explode the fuel.

I do remember someone on TV, talking about hypermilling, and they had a automatic, put it in neutral and shut off the engine while going on a slight down hill (this may help some, if its a fairly long down hill- and your not picking up too much speed, and its not going to be an unsafe act to either yourself or other motorists around you. In other words, its a real specific situation, a certain road you drive weekly/daily , that you can utilize doing this ..... but 99.5% of the time this situation is just a dream.

 

Anyone have a roof rack and notice a difference in MPG?

 

the extra down force from the front wind deflector will lower your mileage, but hardly noticeable over a half mile to the gallon i would say...

if you're looking to save as much on your fuel as possible WITHOUT taking alternative fuel methods into account. i would say spending the extra money to get any carbon fiber body panels that you can I.E. hood, hatch and fenders. sure you'll only be saving some 60-70lbs off the total curb weight, but it's less weight for the engine to be carrying. another area to look at *if you have fiberglassing experience or know how* you can get your self some carbon weave of a tight knit like 4 or 6 weave or higher and replace all the metal in the back rests of the rear seats. glassing carbon weave *carbon fiber* is just the same as fiberglassing, specially when it's just a crude structural job and there's no need for excessive sanding and clean gel coating. this will save a good load of weight just on that. my estimates was around a good 50lbs. just need to make the carbon fiber strong enough to handle about 500lbs without fatigue, cracking or breaking. it would be perfectly safe to do being all that metal only supports the weight of whatever passenger is laying their back heavily on the backrest. other then that, the tie down bar FOR the back rests is the one piece that would be considered part of the vehicle's safety.

 

Replacing your OEM hood/trunk and fenders w/ CF parts would yield an extremely minmal increase in MPGs (ie less than 1MPG increase).

 

Exactly, and the cost attributed to doing those mods is rediculous. Basically all show, and no extra go gumption

Getting back to that roof-mount rack system. No doubt it will be a decrease in mpg.. by how much?? Around town not much if at all(under 30 mph) , but once you start going 35+ mph, highway/freeway usage... I could see a drop from say 40 mpg, to 37-38 mpg.

I am working on a custom mod/experiment in the coming week or so. Its costing me about $25 , plus my time. Once I'm done, I'll share pictures... results, etc.

 

Belly Pan?

 

no... thats fairly time intensive. Plus , to do it right gotta get some kind of hard material.. plastic?? or Aluminum, which would easily be over $25

 

Guess it depends on how your source your material...I have a 12' x 24' thin sheet of stainless steel ($5.00!!!! ) that I have been wanting to use as a belly pan...ive been wanting to do this for over a year now ( .... ) but my motivational levels have not been that high.

Hmm...Ok...I will be waiting patiently until you post some pics of your mod.

 

hmmm... what about xB's with a wing as opposed to those w/o, does that make a diff in mpg?

 

I wouldn't think the factory style wing would make much if any difference. Since it hangs off the back instead of being up in the air like a trunk mounted wind on a sedan.