How to accelerate in P&G mode?

[theholycow]

Originally Posted by sonyhome

I not RPMs, flooring the accelerator, the injector duty cycle is close to 100%. So there's a max amount of gas in the piston. Is the explosion complete (gas fully used)? Is there always enough oxygen for the amount of gas pumped in the piston?

The computer won't let it run that rich. I have never managed to see more than 50% duty cycle. At low RPM, flooring it doesn't increase the duty cycle much vs. partial throttle. If I am light on the gas at a given RPM I might see 8% duty cycle, and if I floor it I might see 12%.

Originally Posted by R.I.D.E.

When you use engine drag (car in gear) you are turning all fuel to the injectors off=DFCO=Decelerate Fuel Cut OFF.

Coasting is great, but if you have to stop or slow down a lot, it may be better to use DFCO. AS long as you can keep engine speed above 1000 RPM you have no fuel delivered to the injectors.

If you need greater acceleration use a lower gear. If you don't need greater acceleration, use the highest gear that you possibly can. When you want to maintain speed use the highest possible gear as soon as practical.

Quoted just to reiterate. That was very well said. I would replace "may be" with "surely is".

Try this. use a lower gear than you would use normally. Once you reach the point where more throttle really doesn't do much of anything, you have reached the best point for economy. Wot will use more fuel than this method. The ideal throttle percentage should be about 70%, could be less but not much more.

Are you talking about your Honda in specific, or all cars? From actual measurements, I can tell you this is not universal. In my VW, injector duty cycle goes down when I go from 80% (maybe 70%, maybe 90%, my foot is just not that accurate) to WOT. I'm at a loss to explain it. At first I thought maybe the fuel rail pressure goes up at WOT, allowing a shorter duty cycle to feed in more fuel; but I can't argue with the gas pump, and using WOT (instead of that 80% target) has improved my FE.

To determine what RPM your enigne stops fuel shut off, just let off the gas in 5th gear and wait until you feel the surge when the fuel supply returns.

Also, note that the surge is barely perceptible, you really have to be looking for it, at least in my vehicles. It is gentler than, for example, the torque converter locking in my truck (which itself is almost impossible to feel).

[sonyhome]

Originally Posted by theholycow

I can tell you this is not universal. In my VW, injector duty cycle goes down when I go from 80% (maybe 70%, maybe 90%, my foot is just not that accurate) to WOT. I'm at a loss to explain it.

Also, note that the surge is barely perceptible, you really have to be looking for it, at least in my vehicles. It is gentler than, for example, the torque converter locking in my truck (which itself is almost impossible to feel).

Could it be that the computer switches mode in WOT, and computes the optimal duty cycle for acceleration, whereas at 80% it does what you tell it and runs too rich without returning any benefits in improved acceleration? (by too rich I means spend too much gas for no extra return, not spitting out unburned gas)

I'll try to look for that surge on my Del Sol. 875RPM is darn close to idle, no suprise there...

[theholycow]

Originally Posted by sonyhome

However, for the CRV, it seems there is no DFCO, unless the Scangauge is wrong. Downhill in "D", I see 0.8GPH used, and up if the grade is steeper and the engine RPMs go up. Shifting to "2" or "1" increases consumption too (slower speed higher RPMs, duh! and no DFCO?).

The ScanGauge has to guess/calculate fuel usage. It can't measure GPH, there's nothing in the OBDII standard for that. I assume that it guesses based on O2 sensor reading combined with MAF, but if so then it's probably correct and your Honda has no DFCO. I have a hard time believing there's no DFCO on the CRV!

Originally Posted by sonyhome

Could it be that the computer switches mode in WOT[...]

Could be. I don't know, but I hope to find out eventually.

[sonyhome]

Originally Posted by theholycow

The ScanGauge has to guess/calculate fuel usage. It can't measure GPH. I assume that it guesses based on O2 sensor reading combined with MAF, but if so then it's probably correct and your Honda has no DFCO. I have a hard time believing there's no DFCO on the CRV!

How can the SG compute MPG reliably and not be able to compute GPH? If what you say is true, then MPG results would be way off when coasting downhill (hard to prove, try downhill coasting for a full tank! LOL). People report that the SG should display "9999" in DFCO, right?

Well is there DFCO for other slush-box A/T vehicles in general?

[monroe74]

Originally Posted by theholycow

The ScanGauge has to guess/calculate fuel usage. It can't measure GPH, there's nothing in the OBDII standard for that.

I'm pretty sure this is exactly true, but I want to add something to help people not get confused.

There are scantools that mechanics use, that plug into your OBDII port and report a lot of things. Some of the scantools report injector data. This seems to contradict what you said, but not really. I believe the folks who made the scantool paid a licensing fee to one or more car makers, and were given data about the proprietary method that maker uses to report injector data via the OBD port.

In other words, the data is not part of the OBDII standard, and therefore it's not easy to get at, even though it does exist, on some cars.

I think Scangauge decided to not to try to get at the data that way, presumably because it would have been difficult and added expense to the product. Maybe a lot of expense. I wouldn't be surprised if the car makers demand a licensing fee on a per-unit basis.

[theholycow]

Originally Posted by monroe74

I think Scangauge decided to not to try to get at the data that way, presumably because it would have been difficult and added expense to the product. Maybe a lot of expense. I wouldn't be surprised if the car makers demand a licensing fee on a per-unit basis.

You are most likely correct. It seems extremely expensive to get manufacturers' proprietary stuff like that.

And, here's proof that the SG definitely calculates/guesses fuel rate:

Originally Posted by Project84

I EOC'd today on my commute and w/ engine off it was still reading 0.07 GPH and at 45mph it was only 477mpg.... this is with engine off!