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Crazy idea or coincidence: From bad to better MPG

2097 Views 9 Replies 4 Participants Last post by  Yves M.
Hi all (I know this will sound crazy and I can not verify more),

Here is the experience I had that seems to have given me better MPG:

First, I do not have great MPG average, I have larger tires (185/60) with more rolling resistance and a heavy foot.

Second, after a night of rain, the first time I apply the brakes I hear a low grinding sound from the side the rain was from. Probably just to remove some rust on the disk, and then everything is fine.

Third, a few days back and after I started moving the car for the first time (before the first Stop sign), I applied the brake while I had not removed my foot from the accelerator. I was crusing steadily at about 20 MPH, and applied the brakes just enough for the pads to touch and not enough to slow the car. For about 5 seconds. I must have had my foot a little more on the gas to keep the speed.

NOW: At that time, I noticed that the IMA battery charging was doing it more easily while crusing at a slow speed and having the battery level at more than half. Since then, the charging happens more frequently and the battery level is higher.

More, I can now have some of the lean burn mode. I did not get it since I put on the larger tires. It now happens.

I see my daily average has dropped by half a liter. Something I could not do before the brake/gas pedal at the same time.

Could it be that applying the brakes and the accelerator at the same time have reset something in the way the car manages the fuel or is it some coincidence with something else like maybe the gas itself.
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Hummm...that is interesting. I guess the computer could always "watch" where the throttle position sensor is when the brake circuit is activated. It also wouldn't be too far fetched for there to be some type of "calibration curve" so that the computer would expect that the throttle was closed and it could start to set up regenerative power. If those two conditions were met, hitting the brake with the throttle still slightly open would certainly "skew" the curve and seem to make the re-gen come on at an earlier time. Keep us posted on the behavior.
It has been almost a week now.

Here is what I remember:
With the OEM tires at 44 psi,: I averaged 4.5 l/100km
With the 185/60 tires at 44 psi: I averaged 4.8 l/100km

After the 'brake and accelerator' pedal incident:
With the OEM: I do not have them anymore
With the 185/60 tires at 38 psi front and 35 psi rear: I averaged 3.7 l/100km

I lowered the pressure for better comfort (bad roads). MPG has been great (not small improvement, it is clear) since brake/accelerate.

Is it possible to do a 'brake and accelerate' test by someone with a manual car that the person thinks it is not showing good mileage while he is trying to.

It is simple: start the car, move in 1st gear, apply brake and accelerator with the engine about 2500 rpm for 5 seconds.

P.S. When I run the car for the first time and after some rain (origin for this tread), the brake grinds. I checked and there are 2 bolts holding the front caliper. One is long, the top one. It is screwed tight and the bolt comes out on the side of the disk. I could see at the end of the bolt that the tip has made contact with the tip of the disk (rusted part).
I have grinded down the bolt to make it flat with the caliper therefore it does not touch the rusted part of the disk (where the pads do not touch) and it removed the grinding noise.
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Yves M. said:

Could it be that applying the brakes and the accelerator at the same time have reset something in the way the car manages the fuel or is it some coincidence with something else like maybe the gas itself.
It's possible, I guess, but not likely. If you assume this is possible, it will return (rather quickly) to the previous state. It will not be a permanent change. Anyway, the ECM continuously monitors all the variables, and they are changing all the time (umm... being variables). The basic programming will not change.

I wonder if this is a mechanical event. It is unlikely that you had any significant drag from your brakes, but I guess that's possible, too. It must have been symmetric (L/R) to not be noticeable.
OK, I have attempted to duplicate your conditions. Just after a local rainstorm (coincidence!) I took the Insight for a short drive around the block. Held it at about 20 MPH and lightly rode the brake for about 5 seconds.

I calculate your figures of 4.8L/100Km and 3.7L/100Km to about 49MPG and 63.5MPG respectively. We averaged about 58.7 MPG on the last tank of gas. The bad part is that my car was just filled up, so I won't have the "same gas" comparison.

One note of interest is that you do not get regenerative braking in this scenario...clearly, the computer gives priority to the position of the throttle versus application of the brake.

I will report back as the "experiment" progresses.
Could it be that it is all about the outside temperature that is giving you that great milleage.
I also noticed a big improvement from last few weeks compare to this week, we went from 15C to 30C. that as to make for some improvement.

Also, to my understanding, bigger tire requires less air so i was told by my tire vendor. So your 38/35 is good!

Thanks Corey very much for doing a test. Look forward to see the results. I did notice a change right away on the instantanious display. If you did not, could be that you already have a good MPG average or the test will not show any improvement. We'll see.

Normand, I thought it could be the temps but for example, this morning was 8C and the tank average went to 3.9 for a few minutes and back to 3.8 (60 mpg). In the last 4 years I never had that kind of MPG in the city and that was with the oem tires.
In the first few days I had the 185/60, I had put more pressure because the MPG was better at 44 than 40. The lesser air is for even wear but not necessarely for MPG

I guess I hit a 'good' twilight zone or something. Cause I get EPA ratings.
OK , here are my last findings:

Like Corey872 wrote, on normal occasions, at startup, applying the brake while the gas pedal is pressed does Not induce regenerative braking

I experienced 3 times the abnormal (although better than my normal) more MPG and SOC:
Again, first start of the day, after 200' of driving and gas pressed, I am still in first gear, I press the brake litly BUT the regenerative DOES engage and show a few green bars. And then I get the better MPG.

There is a relation to having both pedal pressed and having regenerative brake charging that gives me better MPG for the rest of the day. It is not a premanent change.
Interesting...I was going to delay post until I had some "actual" numbers...but since it popped up:

On June 9 (see earlier post in this thread) I attempted to duplicate the same set of circumstances observed by Yves. So far the MPG for this tank (which is about 3/4 gone) is ~58.9 in mixed driving. Which is pretty much equivalent to the last tank.

I also had a chance to take the car on my 50 mile round trip commute to work. I achieved 75.3 MPG on the loop. My personal best so far is 76.0MPG. There was light rain and wet road conditions for the first half of the 75.3 MPG loop while the conditions on my "best" were excellent for the entire loop.

So far, I have not seen anything that I would consider "significant" in the form of mileage gains. However, as I have pointed out and say test was far from scientific. Also I was getting nearly the mileage normally which Yves claimed his car jumped to.

Lastly, Yves...About the regen braking. What I found with my car was when driving down the road, throttle slightly open, and lightly stepped on the brake (RPM ~2500) no regen braking. As soon as I would lift on the throttle (ie ECU would see 0% open) the regen braking would kick in until the engine RPM fell below the cutoff point.

If you are seeing regen with the throttle partly open, is it possible your TPS is mis-adjusted or the ECU is not getting the correct voltage (ie faulty wire?) Generally TPS voltage is ~.5V closed and 4.5V at WOT. IF you had a high resistance connection, bad ground, etc... that voltage may be reduced and the ECU would think the throttle closed earlier. It could be a situation where a component is faulty and giving you poor mileage, while the "fix" is just getting everything back to normal for a while.

I will admit that I am not a big "featherfoot" but my car still manages 55-57 MPG on the interstate (70-75MPH), 70-75MPG on the secondary highways (60-65MPH), and about 60MPG around town.

I will give "The Yves Method" more testing with the next tank of gas. Keep us posted on any additional discoveries!
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Ah AaaaaH!

Thanks for this tip Corey. The TPS could be faulty and I'll try to validate it.

Then maybe this tread should be in the Problem section. I'll move it there.

I just received the MAP sensor that Cakley wanted to depart with, thanks to Cakley. It should be good and I thought that it could be related. I'll replace it with mine. But the TPS is more probable.
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