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I have seen this in the car before and wondered.
2 days ago I got it to happen just enough to try and describe it.

it seams to be more than just hang time.

at highway speed, let the car settle into a speed, back off to work hang time.
*Then after 1/2 a second back off again and incredibly small amount instant will JUMP up 10-15mpg. watching IGN it would jump at that time also form 30's to 41~. the car would lose speed easy if anything happened - small hill or truck passing.
*Next in an effort to better hold speed I found I could push the accelerator down an even more incredibly small amount and speed would hold better and mileage would keep 80% of that jump in mileage. the IGN would also drop down but ONLY by 1.

is this something like Super Highway Mode?

Hi Allen:

___Yes and many vehicles have something like it. This is hang time.

___Good Luck

___Wayne

I'm a bit unclear on this?
You partially lift off the accelerator-the ign advance bumps up a bit, then 1/2 second later give another slight lift and the advance will jump another 10 points and the mpg will increase maybe 25%? On level highway this setting will hold speed or more likely lose speed slowly?

I Why is this written into the ECU ?

I'll have to see if my 5.7 FSP it responds to this. I occasionally see 35-40 mph during lightly powered glides at 35-40 mph or so.

Thanks
Charlie

yep that is what I am seeing.

I have noticed something similar with the 1NZ-FE 1.5 in my Yaris. Not so much the big jump from letting off the gas a second time but after letting off the accelerator, waiting a few seconds, then pressing slightly on the gas I can accelerate getting a higher impg reading. It also feels as if the engine has more power with a lighter touch.

On the reverse side, if I have to accelerate rapidly, for a merge or something, it takes a while for me to be able to get a decent steady driving impg. I am finding that I have to let off the accelerator (major hang time to where I actually slow down a little) for a few seconds then I can press again and get a much higher impg reading while accelerating. Sometimes it takes a few times of doing this for it to happen. Perhaps it is a timing thing where it needs to be a certain time for it to kick in, such as more than 3 seconds or more than 5 seconds or something? Maybe I should try letting DFCO kick in and that might trigger it? Or, perhaps it is all in my head!? Whatever it is, it is a great feeling to see high numbers and feel all the chipmunks working together to speed my to my destination.

I have noticed something similar with the 1NZ-FE 1.5 in my Yaris. Not so much the big jump from letting off the gas a second time but after letting off the accelerator, waiting a few seconds, then pressing slightly on the gas I can accelerate getting a higher impg reading. It also feels as if the engine has more power with a lighter touch.


On the reverse side, if I have to accelerate rapidly, for a merge or something, it takes a while for me to be able to get a decent steady driving impg. I am finding that I have to let off the accelerator (major hang time to where I actually slow down a little) for a few seconds then I can press again and get a much higher impg reading while accelerating. Sometimes it takes a few times of doing this for it to happen. Perhaps it is a timing thing where it needs to be a certain time for it to kick in, such as more than 3 seconds or more than 5 seconds or something? Maybe I should try letting DFCO kick in and that might trigger it? Or, perhaps it is all in my head!? Whatever it is, it is a great feeling to see high numbers and feel all the chipmunks working together to speed my to my destination.

ya sounds simular.

I am thinking the ECU is programed to think if you just accelerated once you might do it again soon so it stays in a mode for more power for a few seconds.

This may or may not be related.

When you apply small increments of throttle, but not enough to dramatically drop the manifold vacuum, then you should have more advanced timing.

I call it the lack of cylinder filling events. To me a cylinder filling event is when manifold vacuum is 0, and you have maximum available compression.

When mani vac is 0, your timing will not be as advanced as it will when mani vac is significant. Mani vac is essentially choking off the air flow to the engine.

In the old days of mechanical advanced distributors, they had a ported vacuum that modified the centrifugal advance movement. The ported vacuum would retard the normal centrifugal signal, which retarded the timing under light loads. Stomp on the gas and the ported vacuum would be practically 0.

This is because your "effective compression" is lower when manifold vacuum exists. In essence with lower compression you get better combustion with timing more advanced.

As far as it being repeatable, I can only speculate as to why it would be inconsistent.

Certain timing controls are based on engine speed, throttle position, and load. This gives you an initial timing amount. Then that value is modified by the knock sensor, which will cause the initial value to be reduced. Generally the intial value will be more than ideal, and rely on the knock sensor to provide feedback for further value modification.

Inconsistent throttle imput would delay the knock sensors modification enough to get a minute amount of knock, so the signal would not allow advance until things had become somewhat stabilized.

Just a WAG, but there is considerable experience behind the WAG,

regards
gary