Help needed with an experiment.

[omgwtfbyobbq]

I was wondering if someone could contribute some bidirectional scanguage runs for the sake of mpg. I don't have a scanguage, or for that matter, an OBDII car, so these would be out of my reach.

I'm trying to figure out if P&G'ing in gear (no engine off, stay in gear) with some average speed is more fuel efficient than cruising at that same average speed. Hopefully, someone could do a bidirectional P&G in gear run, figure out what the average speed was, then cruise at that speed over the same bidirectional run. Maybe do it for a few speeds to see if there's any difference?
Thanks!

[zpiloto]

I played around with this not as an experiment bases but just to see if I need to go further with it. My car is an automatic. I was plusing 5 miles over the posted speed and gliding to 10 under. I did this over a 40 mile test loop with rolling terrain, mixed driving and multiple stops. Traffic is never a factor. Just one run plusing and the other normal driving style. Avg speeds for the loop were 36(plusing) and 40. The Plusing FE was 38.2 and the normal style driving(if you can call it that) was 38.6.
Take the results with a grain of salt. I'm sure there are better way to pulse than what I was doing and with time it would probably make a difference once you perfected the technique but for me with the auto it just not worth the effort.

[omgwtfbyobbq]

Thanks for the input! I'm hoping that the pulsing can do something, but it may be a zero sum game. In that case, my recent spike in mileage (from ~30mpg to 35mpg) is probably because of running 50psi on all four corners and nothing else, which is encouraging in and of itself.

[rh77]

Originally Posted by omgwtfbyobbq

Thanks for the input! I'm hoping that the pulsing can do something, but it may be a zero sum game. In that case, my recent spike in mileage (from ~30mpg to 35mpg) is probably because of running 50psi on all four corners and nothing else, which is encouraging in and of itself.

I do the same as zpiloto. On hills, I'll keep the throttle at roughly 9%. If the speed limit is 55, I go down a hill and get up to 60 (which in most parts of the Country isn't enough to get into trouble). Then I keep the pedal at the same 9% up the hill. I'll generally scrub-off about 7-10 mph in the process, but the FE stays at a great rate. Then on flat ground or another downhill, you get back to 55 or so. This has really helped my primary/2-lane road driving -- instead of using the cruise. The same applies for the Interstate, but it's to easy to get going way too fast if you keep the hammer down (even only slightly).

RH77

[krousdb]

Originally Posted by omgwtfbyobbq

In that case, my recent spike in mileage (from ~30mpg to 35mpg) is probably because of running 50psi on all four corners and nothing else, which is encouraging in and of itself.

Highly doubtful that you would get a 17% increase due to tire pressure unless you were severly underinflated to begin with. More likely the 50 PSI got you 1 MPG. The rest is probably from all of the FE tips and tricks sinking in.

[omgwtfbyobbq]

Well, fronts were at 40psi (45 sidewall), rears at 30psi (35 sidewall), sooo.... maybe 2mpg? If using engine on P&G doesn't work, the only thing I can think of is a reduction in average speed by trying to P&G at 55mph. For the next couple round trip runs I'll try a relatively high speed engine on P&G, and based on my average speed for that round trip, cruise at that speed on my next round trip. All things being equal, I should be able to match the average speed, and since it's ~90% highway, the difference in lights should be minimal, so I can actually figure out if it makes a difference.

Ideally, someone with a scanguage could get instantaneous results, but I suppose I could wait...

[MetroMPG]

Keep in mind: P&G gains are subject to diminishing returns as speed increases. (Aero factors kill the glide length). The fantastic FE numbers you see people achieving with P&G are typically done below 40 mph.

I'd be doubtful that even low speed P&G in gear would net a gain. Add more aero drag at higher speeds and I'd bet that it could end up worse than just cruising.

[diamondlarry]

Originally Posted by MetroMPG

Keep in mind: P&G gains are subject to diminishing returns as speed increases. (Aero factors kill the glide length). The fantastic FE numbers you see people achieving with P&G are typically done below 40 mph.

I would agree. Last week when I took trip with the family, I pulsed to 60 mph and glided to 50 on the highway portion and between 30&50 on the county roads. My FE for that trip(37 miles) was 55.9 there and 56.7 on the way back. While these are respectable numbers, they are substantially lower than the mid 70's to low 80's when I am travelling on the back roads where my average speed is closer to 25-30 mph. Also, my max pulse speed is usually no higher than 45-50.

I'd be doubtful that even low speed P&G in gear would net a gain. Add more aero drag at higher speeds and I'd bet that it could end up worse than just cruising.

I did something like what was mentioned when I had my Durango. I did my P&G and didn't shift to neutral. I don't remember the exact mpg figure but it was one of the lowest I had ever gotten in that vehicle.

[omgwtfbyobbq]

Ah know how to do eet. I just have to figure out how trick the ECU into thinking the TB is closed all the time so I can open it. I have a feeling that during closed throttle in gear, most of the difference in energy compared to engine off in neutral, actually comes from the transmission/differential instead of the engine pumping air since the engine can't pump much air with the TB closed.

edit- yesh, i have asked on another forum and supposedly there is no noticable difference in coast down times in gear between throttle open and closed, so, most of the losses from coasting w/o injector firing is from the rotating assembly. One problem is that with most cars, the injectors start firing at an engine speed (gear independent in older vehicles) that makes low speed, in gear, P&G all but useless since the glide portion is actually the car idling down the street which is proportionally wasteful. Otoh, for higher speed driving, using in gear P&G should result in better mpg versus cruise control at the same average speed, and can be useful if the driver does not want to drive at less than the fuel reinstatement in the tallest gear. In terms of the average speeds where some single drivers are seeing 100+mpg, I don't think it's worthwhile to maximize FE at those speeds when the driver can just as easily bike with an assist, but that's just my opinion. Maximization of health would seem to be a priority compared to maximization of FE. YMMV