Anyone tried this to save gas

Stop making so much sense. You are making my brain hurt.

 

I was driving a manual last night, I rolled all the way from the top down five levels in nuetral and it was damn fun. I was yelling I live life a quarter mile at a time the whole way down.

this may or may not have been in a honda fit.

 

Sure there is. The injectors do turn off while in gear. I know for a fact 100% that they do. The intertia of the vehicle turns the drivetrain which keeps the engine turning. The clutch keeps the engine and drivetrain "locked" together. Your valves still open and close just like normal, there just isn't any combustion occurring.

 

^

Correct answer

 

That means that the compression braking power is only the intake air being compressed in the chambers ?

 

Everything in the engine functions exactly the same, the only difference is that no fuel is being burned.

 

If coasting in neutral on the highway is against the law, then I have been breaking the law for over 34 years. My dad taught me to coast in neutral whenever possible for improved gas mileage. I also coast up to stops, and engine brake all the time.

 

I don't have any proof to the matter, other than experimental, but the injecters do not turn off while coasting in gear. Having coasted down long hills at highway speeds, my engine doesn't cool down. Which it would if it was not burning fuel.
Pumping nothing but air through the engine for a long period would cool both the engine and the emmissions system (catatytic converter) below desired temperatures.

 

They do turn off. My last vehicle had a wideband 02 sensor that I installed to monitor my Air/fuel ratios because it was a turbo vehicle. BTW a wideband is the best and most accurate way of monitoring AFR's. When coasting in gear my wideband readout would display LEAN which for that particular wideband setup that means that my AFRs were greater than 17:1. While coasting in neutral my AFR's were around 14.7:1 because the engine is idling when in neutral.

 

What you are missing here is the temp gauge is not very sensitive, in fact it is intentionally not sensitive in the normal range, if you are 210 or 170 there is no change in the location of the needle. Designed that way so hypersensitive gauge watchers don't get all paniced by a little increase or decrease here or there.

With a scangauge I DO see the temperature drop even though the factory gauge stays in one spot. On a long steep climb i'll see 208 also with no change from the factory gauge.

 

Sorry, 17:1 and Lean is not OFF.
I am talking about long downhills. 20+ minutes of coasting at 50+ mph. On more than 1 occasion. That would have cooled to below normal temps. It didn't. Perhaps there is logic to maintain engine temperature. But there must be fuel to maintain heat.

 

Don't think so. The heater was working and it was cold outside. (Coming back from skiing.)
Obviously, fuel consumption is down for the speed hence the increased milage. But the injectors are not OFF.

 

Not this thread again

 

I have noticed with the Ultragauge that when letting off the gas while in gear, the injectors DO turn off for a brief period of time. However, after a few seconds they start to cycle again at a much leaner mixture. I think that this is to keep the catalytic converters' temps hot for emissions purposes. Remember that the cat's can't maintain heat unless there's exhaust gases moving through them (chemical reactions produce the heat).

Try monitoring short term fuel trim if you have a Scangauge/Ultragauge.

 

Yes they do shut off but you are correct that after it cools some the injectors will briefly pulse the injectors enough to produce heat.

http://www.autoshop101.com/forms/h43.pdf


cutoffgraph by worthywads, on Flickr


fuelcutofftext by worthywads, on Flickr

 

I said that it reads LEAN when the AFR's are greater than 17:1. BTW 17:1 is very lean considering the vehicle idles around stoich (14.7:1). If the injectors are turned off, the AFR's would read LEAN.

20+ minutes coasting downhill without any throttle interaction is a very long time to be coasting downhill, and not typical everyday driving for most people. Perhaps the injectors would pulse in that situation.

Also, the heater still being on wouldn't really matter. Your engine would not cool enough to even notice a difference in the heat. Hence why your heater will work when you crank the truck on a cold day before you reach optimum operating temp.

 

Thanks for the link. Good information, it's even a Toyota document.

 

Eeek don't do that unless the road is perfectly strait!

 

Why only straight?