fuel fuel injection cut off when engine brakes the car

[THE NEW GUY]

does somebody knows if the fuel injection cut off when engine brakes the car operates when driving in forced power drive mode (with a switch connected to the TCU)?

[Green1995SVX]

What? 4321

[92snowmachine]

if i gather what you are trying to ask then no and no. the fuel isn't cut off during engine braking in the first place and the power mode only affects the way the transmission operates, not the engine fueling strategy.

[THE NEW GUY]

Some time ago, I´ve install a DMM meassuring the injection duty cycle in the injector 2 and there was no injection when engine brakes the car over 1250rpm. Below 1250 rpm the injector receives pulses again. That is to save fuel and improve engine brake power. But now I´ve installed a switch to force the power mode on the TCU and I suspect the injectors still inject fuel when braking the car.
Does somebody knows if the injectors still inject fuel while braking the car over 1250rpm with the TCU in forced power mode?

[Green1995SVX]

As was stated above, Power Mode only affects the transmission. It is a transmission mode.

[92snowmachine]

Originally Posted by THE NEW GUY

Some time ago, I´ve install a DMM meassuring the injection duty cycle in the injector 2 and there was no injection when engine brakes the car over 1250rpm. Below 1250 rpm the injector receives pulses again. That is to save fuel and improve engine brake power. But now I´ve installed a switch to force the power mode on the TCU and I suspect the injectors still inject fuel when braking the car.
Does somebody knows if the injectors still inject fuel while braking the car over 1250rpm with the TCU in forced power mode?

i would think that your meter just didn't read the injector on time when you had it above 1250, a multimeter is not really the right tool for that job. in order to get clear and accurate results without the data dropping out of hardware limits or in between scales (which would look like a temporary 0) you will need to use an oscilloscope. if the on time actually goes to 0 then there is no engine braking because the engine is not attempting to maintain it's own rpm and would simply increase in rpm to match the speed of the car as there is no power to resist this action. and again power mode will not affect this in any way.

[THE NEW GUY]

Originally Posted by 92snowmachine

i would think that your meter just didn't read the injector on time when you had it above 1250, a multimeter is not really the right tool for that job. in order to get clear and accurate results without the data dropping out of hardware limits or in between scales (which would look like a temporary 0) you will need to use an oscilloscope. if the on time actually goes to 0 then there is no engine braking because the engine is not attempting to maintain it's own rpm and would simply increase in rpm to match the speed of the car as there is no power to resist this action. and again power mode will not affect this in any way.

Well, you are right and wrong. It´s true a simple DMM may not be accurate reading duty cycle but I use to have an "automotive DMM" (made in china) that works very well in fact reading Duty Cycles within a range. Now, my osciloscope (Fluke 125) does not read duty cycle directly as my 289 wich is better for this task.
About the engine brake, while the throttle sensor is at iddle position and rpm is over 1250rpm, there´s no fuel injection. At this point, engine is breaking the car just like when you engage second speed in a MT when aproaching a curve. You can also use the engine breake putting the gear lever on 3 or 2 on your AT. (do not do this on 1 for common sense). By cutting the fuel injection at this point, engine breaking power is increased because there´s no fuel to burn so the engine tend to stop. There´s no air getting in, so there´s no compression on the combustion chamber, only vacuum = no heat generation. But we do not want the engine to stall so the injection re-starts when rpm going down crosses below 1250rpm.
I was just trying to avoid repeating the test of the duty cycle meassuring in power mode. I think the same as the mayority of you: power mode affects only transmission. But, I better confirm on the wiring diagrams that the power mode signal does not goes to the ecu too...
thanks guys.

[Crazy_pilot]

What's you end goal with this? Determining if the car is as fuel efficient in "Power Mode" as it is in normal driving mode?

I recall a post by one of the European members stating that he ran back to back fuel tanks in both modes and found no significant difference in fuel consumption that couldn't be accounted for by simple driver habits and road conditions.

[92snowmachine]

while you may be able to read duty cycle with a dmm that is not actually what you should be checking for, if you check for injector on time in ms you will see that they don't shut fuel off it just drops to near zero ms. duty cycle and on time are related to each other but not the same thing. even with a cheap dso you will see 0 as a duty cycle when on time drops to low level because as a percentage of time it drops below your hardware's ability to display it.

what are you trying to do?

[Tapani]

There's not much engine brake to speak of while in forced power mode - it's not due to engine management..... but the tranny (OWC 1-2 and 3-4).

Tapani

[THE NEW GUY]

I read that test in europe. As a mater of fact, I confirm it my self in my car: mpg is the same in normal and in power mode. But then I was reaching my exit in the HW 15, Laval Quebec, on my way back home, with the gas pedal completely released and engaged in TC... using the engine break to slow down from 124 to 50km/h; then I decided to switch power mode on and I could clearly felt the engine break lower its effect. Just like if the injection re-started. I know that in power mode there's no TC and I can see the rpm go higher when I connect the power mode, but that means to me that engine breaking power shoud be greather under this condition, just like when I use 3rd to breake the car...
I confirmed yerterday that there's no fisical connection (wiring) between power mode and ECU, so AT mode shoud not affect the ECU decisions.
Anyway, I think I'll reconnect my 289, which have a duty cycle meassuring capacity from 0.01 to 99.99%. If you are traveling at 124km/h, your engine is turnig at 2500rpm. this means an injection freq of 1250 pulses per min or 20.83hz. At 1250rpm the injection freq is 10.41hz.
At iddle (650rpm), EG33's duty cycle is around 22. this means an on pulse of 40.6ms. Fluke 289 can read an injector on time of 1.84ms at this rpm
Fluke 289 can see a minimum injector on time of 0.00025ms.
but this is borring calculus... I'll let you know when I finish my test with the 289 connected.

[icingdeath88]

Originally Posted by THE NEW GUY

I know that in power mode there's no TC and I can see the rpm go higher when I connect the power mode, but that means to me that engine breaking power shoud be greather under this condition, just like when I use 3rd to breake the car...

The t/c unlocking should reduce the engine braking effect, not increase it, because it would allow the engine rpms to drop.

[92snowmachine]

Originally Posted by THE NEW GUY

Anyway, I think I'll reconnect my 289, which have a duty cycle meassuring capacity from 0.01 to 99.99%.

At iddle (650rpm), EG33's duty cycle is around 22. this means an on pulse of 40.6ms. Fluke 289 can read an injector on time of 1.84ms at this rpm
Fluke 289 can see a minimum injector on time of 0.00025ms.
but this is borring calculus... I'll let you know when I finish my test with the 289 connected.

why don't you just measure the on time instead of messing with duty cycle calculations? your 289 can measure .00025ms on time but could never display that in duty cycle because it's less than the .01% display range.

[THE NEW GUY]

Originally Posted by icingdeath88

The t/c unlocking should reduce the engine braking effect, not increase it, because it would allow the engine rpms to drop.

absolutelly right! I was confusing 3rd speed with unlocking tc... I think.

[THE NEW GUY]

Originally Posted by 92snowmachine

why don't you just measure the on time instead of messing with duty cycle calculations? your 289 can measure .00025ms on time but could never display that in duty cycle because it's less than the .01% display range.

But measuring duty cycle tells you what percentage of the period is already high. If Duty cycle goes to cero, then for sure "on time " is cero.
In my opinion, duty cycle is the most efficient way to know if any injector is receiving injection signal. But you need a reliable DMM. An oscilloscope is too expensive.
Other good way to know if there´s fuel injection is reading O2 signal. If O2 signal goes to cero, then there´s no fuel injection.
It´s too cold outside and winter is comming hard here in Montreal... I think I´ll leave this meassurements for next summer.