does the 5mt fit cut fuel completely while engine braking?

thanks

 

Yes, this has been confirmed with Scangauge, etc.

 

What does scangauge use to indicate fuel cutoff?

In Ultragauge, I can see that the Fit sends an AFR (lambda) command of 2.000 and then kills short term trim (its zero and if you're looking at any O2 readings, they go to zero also)... but all that really indicates is the car being in open loop, nothing more. ARF Lambda command (and current reading) is part of the newer UG. The classic UG doesn't have those two gauges.

From what I've read here and there, it seems that's what people are using to indicate fuel cutoff. Not saying its wrong, but it isn't exactly proof either.

If fuel cutoff is supposed to be with injectors off... my AEM datalogs should show that, right? But in all my logs, I've never gotten zero injection cycles unless engine is actually completely off (ie, zero RPM, or key switched off and back on when I had those limps while driving before swapping in the new fuel pump).

Seems to me, maybe it's not really fuel cutoff... more like "fuel minimum."

 

has anyone check the injector pulse width during decel?

thanks for the info guys

 

This is what I remember reading about and it seemed to indicate they were off or almost off. At least enough to be inconsequential to fuel use.

As far as I know all modern cars do this.

 

Well, made two logs just now. One was a very short, two blocks, coasting through a turn in gear. The second log was about 2-2.5 mile drive with various coasting and braking. Also, some in and some out of gear. The one of importance was near the end where I braked to stop while in gear, only popping out near full stop to avoid stalling.

Suffice it to say, except for the beginning of the first log where I was stopped with engine off (working to connect the AEM f/ic6 to my laptop), it logged a minimum of 2% injector duty cycle, never hitting zero. Mind you, it didn't give 2% at high RPM when lifting completely off the throttle. I don't remember the exact number (not too high, maybe 6-10%?), but it was somewhat proportional to the RPM, slowly falling to 2% as the RPM fell to near idle/stalling.

As for pulsewidth... The log doesn't directly indicate that. But can be calculated from the duty cycle and current RPM.

 

out of curiosity why does this matter?

 

Injector duty cycle/pulse width or fuel cutoff?

Fuel cutoff matters to those that are even slightly concerned with fuel economy.

Injector dc/pw matters in a sense that, if the injectors are supposed to be "off" at those times, then why aren't dc/pw zero at those times?

Now, if your intention is to be dismissive altogether... Then that is another story.

 

Much easier to minimize voltage than it is to create a complete cut off. Circuit design wise I mean. That's just a guess of course. 2% is inconsequential in the grand scheme of things.

 

Pretty much every car made in the last few years (or decade plus) uses no fuel when engine braking.

 

Im curious as to why fuel shut off during decelleration would matter? It is something I have never taken into consideration honestly.

 

thanks for the log info... i wondered for mpg concerns mostly, if it was better to coast while in gear or out... i presumed in gear, but then the fit still has manual valves...

 

Cause you could save gas?

Did a google on it last night, and there seems to have been some debate about it. The general acceptance is... it depends on what you're doing.

If you're costing downhill and want to avoid gaining too much speed or if you're trying to slow down or coming to a stop, then coasting in gear and keeping RPM above the threshold for restarting the injectors, by downshifting, will save gas.

On the other hand... if you're just coasting and want to minimize speed loss, you'd want to coast out of gear. The claim is that many engines use so little fuel at idle, that it somewhat offsets the fact that, if you coast in gear, you slow down too much and have to get on the gas sooner to pick up speed.

Some folks have gone as far as straight up shutting off their engines by turning the key from the ON (II) position (of course, out of gear also).

For myself, I'm not much for hypermilling... so I don't drive for those reasons. I especially will not shut off my engine during a coast just to save gas (I will do it if I need to get rid of limp mode however).

I drive with "speed" as a priority. Not so much high speed, but consistent speed.

If I am truly coasting, I'll be out of gear.

If I want to do some light deceleration because the general traffic speed is slowing down slightly, I'll "coast" in gear as a light form of braking.

If I want to do some moderate to heavier braking (like coming to a stop), then hit the brakes and pull out of gear (mostly because I tend to forget and stall at the end if I leave it in gear).

And at the heaviest braking situations, I'll slam on the brakes and hope with engine braking it'll be sufficient to avoid the moron in front of me (like the time a bicyclist popped out of blind spot and tried to cross the intersection/my path on my green). At that point, stalling out is the last of my concerns.

 

^Very good assessment of when and what you should do.

Panic stops should always be two pedals in if you're just trying to stop as fast as possible. I understand what you mean though and sometimes it's better to be in gear to throttle and maneuver, it's situational, just like the gas thing.

 

If you're in gear, you're not coasting: you're braking. It's more fuel efficient than being out of gear and using the middle pedal, though.

 

good info goob

 

I certainly don't disagree with this; still I would like to observe that if you're in a panic stop situation, you're probably not taking the time to think about how many pedals to push—just that you need to stop NOW if not sooner. What actually happens probably depends on whether you're more used to a manual or an automatic, or which you learned to drive on, or something like that.