Archives

I noticed something unusual on my drive home last night. I was less than a mile from work and I had let off the gas to get the car to shift. Glance down at my iMPG and see 9999. I check the temp knowing that is has been said here that fuel cut will only happen when the engine is completely warm. The ScanGauge said the water temp was 155. Meaning that at the time i went into fuel cut it was between 150 and 155.

Looks like I learned something new about my car thanks to the ScanGauge. I will be doing more tests when I can.

Mine goes into fuel cut very early - within the first mile. I think newer models have the temperature requirement.

I always try to say 'somewhat warm', based on my observations in 3 cars.

My Insight seems to require a coolant temperature above 138F to enter DFCO.

I want to say mine will going into DFCO when it reaches the temperature that enables me to shift into overdrive; maybe slightly earlier but around 150F.

My Insight seems to require a coolant temperature above 138F to enter DFCO.
the '09 HCHII too, depending on outside temp, sometimes as low as 127 saw it at 120 once but that may have been because it was being nice about the Auto Stop

I never checked the temperature, so I'll say luke-warm. I've had it happen within a minute or two of my starting the car, which was sitting in the parking lot for several hours.

But I don't think it will happen that quickly if it's cold out, which is a rarity in Florida.

-Mike

My car also seems to go into DFCO only after the engine has warmed to ~150. But I almost *never* have seen it go into DFCO in D below about ~45 MPH. If I get it into DFCO above 50 in D, then it will hold down to 35. But generally, I use DFCO in the city by shifting down to 3 or 2.

Now, if I could only figure out why my TC doesn't like to lock until about 2 miles after my engine temperature has crossed 200.

Also, why *wouldn't* an MT go into DFCO, regardless of engine tempperature? Since there is no TC to slip, wouldn't the engine would be forced to spew out raw hydrocarbons--which would in turn force the catalytic converter to work impossibly hard--if it did not DFCO?

It's my understanding that DFCO can only happen when the computer is controlling the spark and fuel injection (closed loop) rather than the rich-mixture advanced-spark warmup routine. The outside air temperature and coolant temperature are not as important as the temperature of the O2 sensor, as it needs to be very hot before it starts to "read" the oxygen content. I think the Hondas listed above have a heated oxygen sensor and so they switch to closed loop earlier in the trip.

They switch wicked quick, though getting good FE takes a bit, sometimes several miles go by before mine is ready to get to work.

i have not yet seen DFCO in Vibe if temp is under the 135~

Can some explain this DFCO process for me, especially the components that effect the cutoff. When did cars first have this capability and which ones? - Dale

I checked this morning. My 1996 Honda does have DFCO early on. Once the coolant hit 60F, I had it. That's about a mile out from my house.

I'll post this here since it is my topic and related.

I found out that I may be able to use my brakes and stay in DFCO. I had to press the brakes in the middle of a fuel-cut and noticed the 9999 stayed up. I tried it for a longer brake and still stayed at 9999. I am going to try to do it from 50 mph or so and see how long it stays up. One problem is I have to keep a closer eye on the RPMs as they drop very quickly.

Once the coolant hit 60F, I had it.Pale do you mean 160 F?

I didn't mention for those who don't know, when my car DFCOs it seals the cylinders, and the brakes and accelerator don't have to make it start burning fuel again, or even breathing. 10 mph and it starts at least sucking air again, enough torque demanded and it will start burning again.

When in this mode friction losses in the drive train are reduced but not eliminated (why I like to FAS)

I don't have a Scanguage yet. On my new 2009 Toyota Yaris Sedan, the "Cool" light goes out after .8-.9 miles driving out of my neighborhood on a cold morning, and a few seconds after the light goes out the transmission will upshift and the DFCO starts working. I also notice that while online info says it goes back to idle fuel at 1100 RPM, mine doesn't till it's showing 800 on the tach. (And it downshifts just after that on a coastdown with no brakes.)

I wish I had a dfco. Mine cuts the fuel a lot but never cuts completely. The closest it comes is above 46 mph when the TCC is locked up, and stays locked up going downhill. Then seeing impg over 100 after a few seconds is common.

Can some explain this DFCO process for me, especially the components that effect the cutoff. When did cars first have this capability and which ones? - Dale

1 Once the car has warmed up
2 The car is decelerating to the point the engine is actually slowing the car.
- At that point the fuel is cut.

The tires / drive line will keep the engine spinning. As soon as the engine slows to a given point (some were just above idle RPMs) fuel is restored to the spinning engine and it runs once again on its own.
It works just like bump starting a car. Instead of using the starter, use the car to get the engine spinning then give it fuel. It happens so smooth you likely will not know it is happening.

as for what cars will and won't do it I have not seen any data.

Manual transmissions will have better chance without the fluid coupling of the torque converter in an automatic.

I'll post this here since it is my topic and related.

I found out that I may be able to use my brakes and stay in DFCO. I had to press the brakes in the middle of a fuel-cut and noticed the 9999 stayed up. I tried it for a longer brake and still stayed at 9999. I am going to try to do it from 50 mph or so and see how long it stays up. One problem is I have to keep a closer eye on the RPMs as they drop very quickly.

Pale do you mean 160 F?

No, I mean 60F. That's when I get Closed Loop on in-gear engine braking. Whether it actually cuts fuel, I don't know. I'd have to actually test the injector pulses to know that.