My manual-transmission Fit seems to have nearly no engine braking. When I go down a long-enough hill, I can feel the engine braking increase significantly after about a minute. That is far too long for some of the steep hills with curves or stop signs at the bottom where I would prefer a smooth, engine-slowed descent.

On many other roller-coaster hills around here I want to get to the bottom with the highest (safe and legal) speed. If even a little engine braking is too much I'll apply a tiny amount of throttle to prevent the engine from slowing me too much.

Now I developed a superstition that I have trained the ECU to leave the butterfly open. Perhaps it would be better to go down hills with the clutch depressed or in neutral and then match engine speed at the bottom and resume powered driving. There is little enough traffic here that this would often be safe.

Questions. Answer one answer all:

1. Does the ECU use the butterfly in the throttle body to increase or decrease engine braking?
2. Does the ECU change the butterfly opening according to how the car is usually driven?
3. Does a ScanGauge or other OBDII reader show throttle-body butterfly position?
4. Why would the ECU not close the butterfly a bit when I touch the brake pedal?
5. Has anyone else experienced anything like this or am I simply deluded? My comparison for engine braking is skewed by usually using carbureted motorcycles that have great power-to-weight ratios and corresponding enginebraking-to-weight ratios.

These may not look like hypermiling questions, but they are related to the way I drive to get 42mpg and this is the sub-forum where people would pay attention to this stuff.

Thankyou verrmuch.

 

What gear are you engine braking in? I find mine doesn't do much braking in 4th and 5th. I have a very steep hill I go down every day and take it in 3rd.

The Fit is fairly light but not featherweight.

Most scan tools should tell you throttle position. You can look at the instant MPG gauge as well. If it's pegged at 80 in gear the throttle is closed and injectors are off. It will also show this coasting at a decent speed idling in neutral because it's barely using any gas idling, but that also means the throttle is closed. Throttle open = injectors on. You will not see the MPG gauge pegged if you're on the throttle even downhill from what i've seen.

 

Today I noticed the engine braking (eventually) increase in 2nd gear (construction traffic on a hill). Other times I'm looking for engine braking in 4th or sometimes 3rd These are 45 to 50mph roads and I don't enjoy engine braking at very high RPM. I'll try different gears to see. Thanks.

Throttle position is different from the position of the butterfly in the throttle body. No? The change that I can feel means that the pedal is not physically linked to the butterfly and the Throttle Position Sensor is usually the device that tells the ECU what the driver's right foot is doing. I also believe that the injectors can be shut off and the throttle-body butterfly can open or close to make the engine work harder against intake vacuum. Isn't that what the controller for the automatic transmission does in response to the tilt sensors?

When I'm very lightly using the pedal to prevent engine braking the MPG meter is often still pegged at 80 although I suspect that my foot (what I think of as throttle position) is probably causing the butterfly to open and probably causing the injectors to fire. MPG is probably closer to 80. When the injectors are off the MPG is infinite.

Perhaps I should shut my big mouth (or fingers) until I can make measurements to back up my suppositions. I'm sure, though, that I will learn here. The suggestion to try lower gears sounds useful. Thanks.

 

Not sure how the auto trans and cruise control witchcraft works, you could very well be correct on that is indeed how it controls speed. I do not know.

4th and 5th gear are fairly long gears. I believe I took 4th to 115mph (closed course disclamer, etc), so dont expect much braking out of it. 3rd goes to 80 mph, don't be afraid to use it on the highway, I think a lot of people only use 4th and 5th on the highway being scared of all the noise

Edit: That is for M/T, I am not sure about A/T offhand but i'm sure they're even longer and don't have time to look right now.

 

I think of all the MT gears as being very short. The engine turns at 33% higher RPM than the AT at the same speed in top gear (or, conversely, the engine with AT turns at 25% lower RPM at the same speed).

I'm sure willing to downshift to pass. That's the only way 1.5L will accelerate this ton+.

My mention of the AT is because someone on this site mentioned that it has tilt sensors that add engine braking for downhills. I have the MT.

 

Sorry, comparatively long gears (to third). 4th is overdriven slightly I think to make up for the final drive, it's a compromise between power and economy and does neither exceptionally well.

 

I feel engine braking in 4th and 5th.

I also weigh 240-250 pounds depending on how hard I do my work outs when Im off duty.
Look at your screen in your gauges, gas mileage should max out when its engine braking. If its not maxed out, its using the throttle a bit.

If your engine is cooling too much from a LONG hill coast, the ecu WILL throttle it slightly to keep fuel injected to maintain operating temp.

99% of the time, OBD2 vehicles kill injectors with no throttle and coasting in gear

 

I think the basic "problem" you're encountering is that the Fit's engine doesn't really have a lot of engine braking power; it's pretty efficient, which means there's not a whole lot of parasitic friction, and it's not very large displacement, so there's relatively little pumping loss. It's not a retraining of the ECU or anything along those lines—or, at the least, I very highly doubt it is. 13fit is entirely correct that cars with EFI (including the Fit) generally cut off all fuel to the engine when descending hills in gear, since it's an easy way to save fuel with essentially no bad side-effects. On some cars, it's fairly noticeable when this happens.

Coasting down a long hill in neutral and relying solely on the service brakes seems like a very poor idea. You'll wear out your brakes sooner, and if you try it on a long enough hill, quite possibly overheat them and have a rather scary moment or worse.

The increase in drag after some time may possibly be due to the alternator kicking in or the A/C compressor turning on or something similar? Just a couple of wild guesses there. I can't say I've ever noticed the effect myself.

(The AT's engine braking feature is primarily an automatic downshifting when necessary. I don't know if it also manipulates the throttle body on the engine in any special way.)

 

Very bad idea. I described two different kinds of hills, the ones where I want engine braking and the ones where I don't. I would only use neutral when I don't want any braking at all. I'd still rather leave it in gear which is why I've been pressing the throttle pedal just a tiny bit. I can feel the reduction in braking even though the meter still shows 80MPG.

I'll try to notice what causes the change. Thanks for those suggestions. I know that sometimes there is useful engine braking and sometimes there is nearly nothing. I wondered if it's providing nearly no engine braking because I keep asking for nearly none. On different hills. The difference is not entirely the gear selected.

I know that the Fit can have useful engine braking even if it's just 1500. Working against a closed intake is enough for control. While hills here can be longer or shorter, it's still the east coast and not like "hills" in Colorado or even near here at the Appalachians.

 

Long stroke, small bore makes for a poor engine brake. This is the L15's problem with engine braking and why you need higher RPM to effectively engine brake with this motor. That and using gear multiplication are essential.

This is why you can't expect much out of 4th and 5th unless it's a fairly shallow grade.