Deceleration Fuel Cut Off

[California98Civic]

Originally Posted by Hypochondriac

I read that for automatics to enter dfco you have to be in d3. Does anyonr know if that's true? I haven't tested it yet. I'm worried if I shift into d3 whie driving I'll ruin the transmission

Nah. That does not sound correct to me. I would think it is all about throttle position and RPM. With throttle closed and RPMs above maybe 1500, or perhaps 2000, I would think your car would slip right into DFCO. You might switch gears like that to raise the RPM above a necessary threshold but it is not likely a requirement that you be in D3 specifically.

[puddleglum]

Shifting to d3 won't do any harm unless you were going extremely fast. You are just doing manually what the trans normally does automatically. I agree that doesn't sound right for DFCO though. Not all engines have the same parameters for DFCO (my Rondo will only cut fuel below 2000 rpm) but it won't require any abnormal input from you to cut in. If you meet the conditions, it will work.

[JockoT]

My previous car was a Volvo S40 automatic, and at anything other than high speed, lifting off the throttle caused the revs to drop to about 1200 - 1500 rpm. There was so little engine braking. From what I understand, for DFCO you need the engine braking to keep the revs above the threshold (as you say, about 2000 rpm). The only way I got appreciable lower speed engine braking was to drop down to D3.
I believe the torque converter didn't lock up until 50 mph in Drive.

[fearlessjoe]

It won't nessacerally kick in at the same rpm in different gears

After using my scan gauge for a few tanks now mine will will kick in at much lower rpm in high gears at speed then it will at lower speeds and rpms.... Which isn't something I saw coming

I often find it more efficient to roll in neutral down shallow hills

[JockoT]

My ScanGauge is ordered, and on its way. What I am doing meantime is coasting in neutral then going back to a high gear when I need to control my speed. My Jazz/Fit is rather light and doesn't build up a great deal of stored energy. On a shallow downgrade, in top gear, it will slow to an unreasonable speed very quickly. In neutral it goes on for ages.

[spdfrk]

Look in torque for the upstream oxygen sensor output. If you're at 0, then you aren't burning any fuel and you're in DFCO.