Shifting Tactics

[GasSavers_worthywads]

I've been doing some experimenting with coasting in neutral vs. in-gear with my scangauge. Here are my observations.

1. In a 2.7L Tacoma I don't think it ever shuts the injectors off complete during in-gear coasting. I tried reving as high as 5500rpm in 2nd gear and then coasted. I saw a drop from 1.9 gallon per hour just after letting off the throttle, then 1.1gph at 4500 and 3500 and then .6gph at 3000 or so. Conclusion, for this engine in-gear coasting doesn't reduce fuel use.

2. During idle my fuel usage is .3 gallons per hour, and during in-gear coasting it is .3gph or greater. In-gear coasting at 2000rpm is .4gph, I plan on going through the range of higher rpms to see how much gph rises. Conclusion, below 1800rpm it doesn't gain anything by dropping into neutral unless in-gear slows you down faster than you want.

3. Going up hills keep it in the highest gear that doesn't lug, higher rpms seem to always mean more fuel use on this truck.

[MetroMPG]

hi worthywads -

Originally Posted by worthywads

1. In a 2.7L Tacoma I don't think it ever shuts the injectors off complete during in-gear coasting. I tried reving as high as 5500rpm in 2nd gear and then coasted. I saw a drop from 1.9 gallon per hour just after letting off the throttle, then 1.1gph at 4500 and 3500 and then .6gph at 3000 or so. Conclusion, for this engine in-gear coasting doesn't reduce fuel use.

i have a scangauge too. my car's service manual states that the injectors are off when engine braking, yet the SG doesn't reflect this.

i've talked to a number of SG owners (including JanGeo on this site) about this and nobody's SG is showing "injectors off". i believe it's a SG bug.

[GasSavers_worthywads]

Originally Posted by MetroMPG

I have a scangauge too. my car's service manual states that the injectors are off when engine braking, yet the SG doesn't reflect this.

i've talked to a number of SG owners (including JanGeo on this site) about this and nobody's SG is showing "injectors off". i believe it's a SG bug.

Tried to contact SG off their website but I get a error?

I'd like a description of how the gph is measured or estimated.

After the first 3 fillup calibrations I have been off at most .1 gallons on any tank, though every fillup has been actually more by this little bit than the SG. I'd think the Fuel Used would be way off if the SG is wrong about engine braking. Then again if my driving is similar from tank to tank my fuel adjustment could be compensating. I haven't taken a long trip with minimal engine braking, it would seem on such a trip the SG would then be way off.

Can't seem to find any specifics on fuel injector function during engine braking for my Tacoma.

Aargh.

[JanGeo]

Yeah I asked my brother about it and he said that there is a minimum amount of gas being injected with no throttle and by downshifting the rpm goes up and thus they inject the minimum amount at a higher rate thus using more gas. I got 66mpg 3rd gear 35mph 120-150mpg top gear in this case I think using the brakes a little will be better as they need some use once in a while anyway. I also see the slowdown in top gear until about 1000 rpm (20mph) then the engine kicks and it's time to throw in the clutch. I did one ScanGauge fillup calibration - second one is today as the gas light has been on for a few miles - in town short trips with really sucky mileage like 17mpg 0.5mile trips up and down hills. Maybe we should wire LED's to the injectors to monitor the injector pluses and get a light show to boot!

[Sludgy]

I suspect that auto engineers don't map the fuel to zero when coasting in gear because of pollution control:

If the fuel is shut off completely while coasting, the catalyst will cool off quickly because unheated air will flow through the exhaust. The car would never meet emission standards if the catalyst was cold every time you go back on the throttle.

[krousdb]

Originally Posted by Sludgy

I suspect that auto engineers don't map the fuel to zero when coasting in gear because of pollution control:

If the fuel is shut off completely while coasting, the catalyst will cool off quickly because unheated air will flow through the exhaust. The car would never meet emission standards if the catalyst was cold every time you go back on the throttle.

My Honda shop manual says that the fuel shuts of when the throttle is closed and rpm's are above 1100. The Honda OBD training manual states the same thing. And the SuperMID confirms this showing the injector pulse width as zero when the engine is at normal operating temperature. So it would appear that Honda has figured out how to do this without affecting the catalyst.

[Sludgy]

I'll bet Ford and GM haven't figured it out....

[philmcneal]

Originally Posted by Compaq888

Here is how my auto does it. When I'm at speed let's say 30mph. If I want to slow down or just coast I just release the gas and the rpms go to 1000rpm or lower and the car keeps rolling and only loses a little bit of speed.

I usually coast 1-3 blocks If I see a stale green light or yellow or red. If nobody is around I coast as much as 4-5 blocks to the light.

maybe that's why camry's automatics get such good mileage. They coast for such such a long time if almost putting it neutral does not affect its coast at all (unless hill is super steep).

[JanGeo]

Hey A few tests done going up hills in different gears - steep hill I go up and down every day seems 3rd 18mpg 4th 21mpg 5th 25mpg speed 29mph about 10 degree slope so higher gear lower rpm better mileage.

Coasting in gear (standard) the faster you go the higher the mpg so if in neutral you coast faster and get better MPG unless you really want to slow down put it in neutral and coast faster. Fuel shut off calculations in the SG are not possible division by ZERO!!! DUH!!! but I see the same kick at about 18mph to 20mph depending upon idle speed hot cold etc. when slowing down in 5th and it seems to provide constant engine braking until about 20mph and the fact that it shows a decreasing mpg reading indicates that it is injecting a constant amount of fuel over the range of speed. Killing the injectors will not change the SG reading because it is monitoring the computer not the injector signal. It will perhaps vary the braking action as you kill the small amount of fuel injected if it is injecting. Again with no change in mpg with engine turning faster or idle then it comes back to the SG minimum injector setting.

Another recent thing I have had happen to my in the xB is sticky / no fast idle with engine cold and wet low temps so that when I back off the gas to shift the car quickly tries to slow down before I can get the clutch in where it usually cuts out a little after the clutch is in unless I let off the gas a little ahead of time before clutching.

[MetroMPG]

hey, is that the official scangauge builder's response on the "injectors off" issue? did you write to him?

the scangauge seems able to divide by zero (i mean figuratively - it uses some other calculation mode) when i kill my engine with the new switch.

good info on the hill climb gear/mpg - thanks for posting that.