Hypermiling techniques that are invalid (potential mechanical wear/cost)

[cfg83]

Clev -

Originally Posted by Clev

I can't confirm that that applies to all FI cars.

In my downhill run, the exhaust on the Clunker burbles slightly when engine braking and the vacuum increases slightly (and engine braking increases slightly) with the key off. This leads me to believe that a small amount of fuel is flowing. This is a '90 with PGM-FI.

Yeah, the older the FI car, the less likely it has DFCO (deceleration fuel cut off). I am pretty sure my car does not have it either. With my digital AFR (Air Fuel Ratio) gauge, I can see the AFR go lean when I hit the brakes, but the lean condition doesn't last for the whole brake event, it goes back to 14.7 . This implies to me that the engine is still getting fuel. Also, when you brake in-gear and you approach idle RPM, the fuel is restored to avoid stalling the engine.

CarloSW2

[Christ]

Originally Posted by cfg83

Clev -



Yeah, the older the FI car, the less likely it has DFCO (deceleration fuel cut off). I am pretty sure my car does not have it either. With my digital AFR (Air Fuel Ratio) gauge, I can see the AFR go lean when I hit the brakes, but the lean condition doesn't last for the whole brake event, it goes back to 14.7 . This implies to me that the engine is still getting fuel. Also, when you brake in-gear and you approach idle RPM, the fuel is restored to avoid stalling the engine.

CarloSW2

I should have said "in the last 10 years or so", instead of grouping all FI cars together like that.

The only way I know to test it is to start engine braking at 2000+ RPM and use an instrument to check for fuel flow, like an injector pulse width identifier.

You could also use an AFR, I suppose, since you'd be going lean as hell with no fuel input.

Oddly, I'm still unsure whether my 4th gen Civics had this setup or not. I never tested for it, but I've seen claims that the older Hondas actually were designed with it.

[SentraSE-R]

Deceleration fuel cutoff in my '02 Nissan Sentra and '06 Scion xB differs considerably. My wife's '06 Hyundai Elantra doesn't have it. So you can't tell from the age of the car whether it has DFCO.

Both the Nissan and Scion have to have the throttle position sensor at idle, open loop, transmission in gear, and rpms above a certain level. The Nissan's rpms have to be >2500. The Scion only >1500. So in sixth gear, the Nissan doesn't go into DFCO unless the car is rolling >65 mph. The Scion goes into DFCO at any speed above 35 mph. Both will stay in DFCO below the initial rpm, but they have to be above that limit to enter DFCO. In practice, I can let the Scion coast down any hill and be sure it's not using fuel. The Nissan, OTOH, has to be in a lower gear to get fuel cutoff.

[basjoos]

One quick way to test if your car has DFCO is to tune your radio to an unused AM channel and turn the volume up so you can hear the static coming from the ignition system. When you release the throttle and start engine braking, if your engine goes into DFCO mode, you can hear the ignition system cut off on the radio.

[elhigh]

I drove about 175K miles without hypermiling, and the last 20K or so feathering the throttle, shifting up....well, I guess I've always shifted up at the earliest possible opportunity. But I'm still on the first clutch, brakes go a long time, tires last around four years or so. It makes sense to amortize cost of repairs into the driving costs if you detect a change in vehicle component lifespans. But what if nothing has changed?

Sorry guys, I've got one of those deathless mid-80s Toyota pickups. I haven't had to replace anything serious yet, I don't have anything to amortize.

I expect a kid, learning to drive a clutch, to finally kill this one and then maybe I can get something that doesn't chatter when it rains. Hello, Centerforce!

[Christ]

Nah, that clutch dies, get yourself an L-series diesel and swap it in. :P

[cfg83]

SentraSE-R -

Originally Posted by SentraSE-R

Deceleration fuel cutoff in my '02 Nissan Sentra and '06 Scion xB differs considerably. My wife's '06 Hyundai Elantra doesn't have it. So you can't tell from the age of the car whether it has DFCO.

Both the Nissan and Scion have to have the throttle position sensor at idle, open loop, transmission in gear, and rpms above a certain level. The Nissan's rpms have to be >2500. The Scion only >1500. So in sixth gear, the Nissan doesn't go into DFCO unless the car is rolling >65 mph. The Scion goes into DFCO at any speed above 35 mph. Both will stay in DFCO below the initial rpm, but they have to be above that limit to enter DFCO. In practice, I can let the Scion coast down any hill and be sure it's not using fuel. The Nissan, OTOH, has to be in a lower gear to get fuel cutoff.

Thanks for posting this. You made me look. I *do* have DFCO after all, just like the Nissan. Today I tested this going downhill in 3rd gear. It went lean until I went below 2500 RPM. I didn't see this before because I am below 2500 RPM most of the time. Because of the way I drive, I never saw it, .

This implies to me that I have a DFCO operating window. On steep (down)hills I can put the engine in a gear that keeps the engine above 2500 RPM.

CarloSW2

[Christ]

Originally Posted by cfg83

SentraSE-R -



Thanks for posting this. You made me look. I *do* have DFCO after all, just like the Nissan. Today I tested this going downhill in 3rd gear. It went lean until I went below 2500 RPM. I didn't see this before because I am below 2500 RPM most of the time. Because of the way I drive, I never saw it, .

This implies to me that I have a DFCO operating window. On steep hills I can put the engine in a gear that keeps the engine above 2500 RPM.

CarloSW2

Woot for better mileage! I'm sure there's lots of places that you drive that would allow you to do this as well!

[roflwaffle]

Originally Posted by Christ

I should have said "in the last 10 years or so", instead of grouping all FI cars together like that.

Based on what I've seen, it's actually closer to most vehicles in the last twenty years or so, depending on location/fuel system type. Vehicles w/ mechanical FI tend not to have fuel cutoff, as do some carb'ed vehicles, but near the end of the carb's use, some were fitted with add-ons that cut fuel depending on manifold pressure, and just about every vehicle w/ electronic FI I've head about has it.

[SentraSE-R]

Cool, CarloSW2. DFCO is handy on those really steep downhills where I can run the AC and slow the car down both, and not use any fuel doing it! The Scion's readiness to enter DFCO at lower rpms makes its DFCO much more useful than the Nissan's.