105 MPG coast
 

I drove home from Wal Mart today and did a down hill coast (engine on in N) right before getting exiting on the off ramp. No big deal I've been doing this plenty of times. This time was different though. Today the SG2 reported 105MPG. It has never reported over 75. It stayed in the 80 to 90 range all the way down. Do you guys think it's because of the grill block that I added or maybe because I had the 19.4% correction on the SG2 last time I filled up?

I don't think it would be the grill block when you're in neutral. It's just your idle gallons/hour times you're speed. (unless you got coasting faster than usual.) Was it a blistering hot day? I had a great coast like this just yesterday and first saw 100+mpg. On my good coasting hill the car had already heated to where it reported 0.5gph in neutral versus 0.6gph. Bam, 20% difference right there. And who knows it might have been right on the cusp of rounding to the next tenth, so maybe it was a smaller difference than it appears. But 112mpg sure looks nice.

I started coasting at 40mph, which is normally what I coast on this hill. It was pretty hot but not unusual for where I live.

nice #s just keep working on it! you have improved really quickly and its sweet to see

I'm trying. We're probably going to New Orleans this weekend. About 70 miles from Biloxi. What would be the most effecient speed on a 70 mph I-10?

It seems somewhere between 40 mph and 50 mph.

So an off the wall and possibly bad idea I thought about was, your car is an auto and you don't really want to turn off the engine while rolling. How about hook a button up to the injectors so that you can stop them from firing and sit there and tap on the button so it is only getting gas half the time. That would double how much mileage you are getting while coasting in N. The car would idle badly like that but as long as you let it get enough gas not to die it should be ok.

Of course since it is probably an OBD2 car, the computer will probably hate you if you try it.

I wonder if there is some kind of electric booster pump that could be added to the trans so the fluid could be circulated while the engine is off. That would be a great way to let an auto trans do engine off coasting.

Coyote X I had the engine on in N. Please re read first post.

Coyote X: The idea you had doesn't work. The car uses the oxygen sensor to try to maintain a optimum air/fuel ratio. When you just shut an injector off, all it does is to add more air, but without fuel, so the computer tries to compensate and, well it doesn't work well.

popimp: From the scangauge data you got and some testing, I found that I have to hit about 43mph for the transmission to go into 4th and to lockup. Anything lower than that, in speed and either the lockup is not engaged, or the transmission is in 3rd gear, either of which equate to lower mileage.

If your on the interstate, I don't think you can legally go less than 45mph, but I would drive fast enough to stay out of the way of the Semi's. I think you'll still be surprised by how much of a help the grill block will make.

popimp,

Firstly, I've been following your struggles to improve your mpg since we've both got similar cars. Based on my recent experience, "getting out more" seems to help raise your mpg because you're travelling closer to highway speeds than city speeds therefore should raise your mpg closer towards the highway mpg and away from city mpg. Your mileage may vary but on my relatively long distance drive, I was puttering along at 55 mph or less due to at least three traffic jam pockets and got bored on the way home so was practicing pulse & gliding up to 60 mph then back down to 55 mph. That resulted in a relatively astronomical mpg boost to 28.32 mpg. For a frame of reference, the posted speed limit on the highways for my trip was 65 mph.

Godslow popimp. :)

I didn't really think it would work but it was worth a shot mentioning it :) That pesky O2 sensor just keeps taking all the fun out of goofy ideas.

On your car does the converter stay locked up when coasting in gear so it coasts with the injectors off like a manual trans car would do while coasting. If it does I wonder if coasting in D with the injectors off but not coasting as far before having to resume driving would be better than coasting a longer distance in N but using a small amount of gas idling the engine?

I'm suspicious that the scangauge recalibration might have been the biggest factor in the change you saw. Was the change in the right direction to explain your improvement?

That said, the grille block should help you coast a little faster, so there is some real improvement in there, most likely.

45mph :o ... probably unbearable though.

Find out! Take it out on a flat road, warm up and plot a speed<->mpg curve like I did when we were talking about it way back. I found a sizeable difference because of the aero just between 45 and 50. If you find that grill block flattens your curve out past 45 a ways I'd love to know.

Coyote X -

Could the button that turns off the injectors also cutoff the signal from the 02 sensor(s)? In that scenario, I think the car would go into Open Loop, right? Open loop may not be as efficient as closed loop, but it might be better than the ECU/PCM's reaction to the 02 sensor.

CarloSW2

Bill in Houston -

This is real easy to check if you don't use the ScanGauge for gaslogs. Just coast down the same hill with and without the correction factor.

CarloSW2

Carlos, taking the O2 senor off-line could do the trick. I think that is one of the ways to overcome the mileage reduction I saw when I was experimenting with my MAP sensor mod.
Edit: Also, the correction factor could possibly account for the gain. I would sugest trying Carlos' idea and do back-to-back runs with the different SG values to verify it.

Do you mean 28.32 for the whole trip? Ah looked at the gaslog, that's for one looong day on the highway. Pretty good including the endpoints.

At highway speeds I've been seeing negative value to trying to pulse and coast, though. The drag brings it down too fast. Let us know if you get some good comparative data and what your secret is to pulsing a minivan.

:D :D :D

savoF3 -

For engine-on-neutral-coasting, the GPH option is a good variable to observe on the ScanGauge.

In terms of rounding, you can change the units to Liters in order to see LPH instead of GPH. The LPH will give you better precision :

0.5 GPH = 1.89 LPH => 1.9 LPH on ScanGauge
0.6 GPH = 2.27 LPH => 2.3 LPH on ScanGauge

Conversely :

2.0 LPH => 0.53 GPH
2.1 LPH => 0.55 GPH
2.2 LPH => 0.58 GPH

I should make myself a handy conversion chart.

CarloSW2

Well I've coasted down the hill several times before with the SG2 and got about 75mpg. I guess at a -19.4&#37; correction this would equate to about 105mpg. 75 is about 71% of 105. With almost a 20% correction this would be about 91% give or take. So it was probably the correction factor.

Question about the P&G, or pulse and coast I guess. If I did the method of speeding up to 60 and using the coast function of the cruise control to drop to 55 then cruise back to 60, would this be the same as turning off the cruise then getting the speed back to 60 manually?

I haven't used cruise control much in the past but, from what I remember, most CC's try to get back up to speed as quick as possible which means they may "push" the pedal harder than what you might do manually. Many people say that your foot can get better FE than CC but it's a WHOLE bunch more effort to do it yourself.
Edit: I just checked out your garage. Nice choice of lubricant and filters. ;) I'm using the 0W-20 in the Prius.

Shutting of the O2 can cause a problem with your emmisions if your trying to be green.

Which by the way, is why I never went there.

What diamondlarry said, plus "coast" on the cruise control will coast in gear. It'll drop fast from 60 to 55.

I think 15mph under the max speed limit is safe (this might be a law - you can get a ticket for driving to slow, causing a hazard) or you'll have to turn your flashers on as do big trucks do going up hills. this way someone doing 85-90 mph will see you and have a chance to slow down or change lanes vs you might get rear ended without flashers. or have one of those big dump trucks with the crash zone cushion following you :)

savoF3,

The return leg was late at night so I was fatigued before the leg began. So I was just pulse and coasting not only to try to increase my mpg but the more important reason was to help keep my mind awake and alert to prevent boredom induced falling asleep at the wheel. Man, pulse and coasting does utilize more of your attention and therefore brainpower to drive. Fortunately, by returning back to familiar road sections near home helped me perk back up due to "home sweet home" emotions so I stopped pulse and coasting at that point.

popimp,

Purely from a technique comparison they would be different since you're doing different things in each technique.

So with the first technique, you're basically cruise controlled at 60 mph then push the [coast] button down to 55 mph then re-engage cruise control so it automatically accelerates back up to 60 mph. Am I understanding the technique correctly? If so, based on "gut instinct" since I don't have a ScanGuage, the "automatic acceleration from 55 mph to 60 mph" is probably going to involve an RPM spike to like 2500 rpm, achieve 60mph then RPMs drop back to the appropriate RPM for 60 mph. So since it's probably going to spike, I would recommend against this technique.

Now from a pure no cruise control technique, this may result in spending too much time with your eyeballs inside the car by looking at the tachometer and the speedometer to see if the RPMs are low and the speedometer is bouncing between 55 mph and 60 mph. That would probably distract you from safety of driving by looking outside the windshield for other traffic. Increasing fuel economy and saving fuel expense is one thing, but unless you're the only car on the road, you could also "fuel efficiently collide" with another car. So like the first technique, I'd recommend against it.

What I did was to smoothly and slowly accelerate up to 55 mph then set the cruise control. Then, on the flats and gentle downhills, I would add like an extra 100~200 RPM to help nudge the speed up to 60 mph. Then once it reached 60 mph, I took my foot off the accelerator and disengaged the cruise control so that my RPMs dropped as low and fast as possible. However, at around 57 mph or so I re-engage the cruise control so that the tachometer pops up from 1500 RPM to 1800 RPM instead of spiking to like 2500 RPM had I re-engaged the cruise control at or below 55 mph. YMMV for your 2006 model. When "brain overload" happened, I just temporarily discontined pulse and gliding and just sat at 55 mph with cruise control.

I hope this helps.

minic6 -

Yup, I was actually waiting for someone to point that out. I would only do it for experimental purposes, not as a general solution.

:D <- Green

CarloSW2

Thanks for all the feedback.