Driving Techniques with Auto trans
 

Hey guys i have been trying to get better at the whole P&G thing. I also have tried shifting in to nuetral going downs hills and on straights(get like an extra two miles for every five) so it seems benificial. But i am worried that, that is really bad for my trans since it is an automatic. Also i did have a lower than average FE this last fill up... putting it in nuetral. When i switch back into drive the RPMs shoot up almost like as if i was down shifting. Would this cause for lower FE.

Also can anyone explain to me other driving techniques that could help out my automatic diesel??

Thanks :D

Shifting into N at speed will not do damage to an automatic provided you leave the engine running. As long as the engine is running the transmission pump is running and lubricating the tranny. What you may want to do is what we call "rev matching". Take my truck for example. Traveling @ 60 MPH on flat ground the engine runs @ ~1,500 - 1,600 RPM. If I shift into N at this speed the RPM's fall to ~900 - 1,000 RPM. Before shifting back to D from N I would lightly touch the accelerator and bring the RPM's to about 1,500.

You're on the right track, and good luck. You'll get better, and tailor your driving to what works best for your vehicle. Also, if your vehicle is a 1996 or newer I highly recommend buying a Scangauge so you can monitor your FE in real time.

-Jay

depending on the year (1995, I know) your car might DFCO which makes it almost useless to shift into neutral. no gas is better than less gas.

DFCO = Deceleration Fuel Cut Off. this is where when no throttle is given so the engine cuts off the injectors and the tires are actually spinning the motor. this only happens at certain conditions though. I said depends on year but I can't tell you if your car has it or not. mine doesn't but my wife's does.

also I have done some testing myself and found that neutral coast doesn't really work for me. two things that suck gas is RPMs and LOAD. at highway speeds, coasting down a hill (in gear) I will be pushing 2,000 RPMs but my load will sink into single digits. If I were to put the car in neutral, RPMs sink to 700 or so but load goes up to 25 percent.

I would recomend a scangauge but i don't think you are OBDII compatible because of the year. I know some cars had it in 1995. that may be something to check on.

I looked on www.scangauge.com and it doesn't appear that a 95 Mercedes is compatible. Looking down the list it looks like there are several 96 & up Mercedes models that are not compatible.

Depends on the amount of engine braking you get. Some cars will keep gliding for a long time and the engine will barely brake at all, but on some cars it takes a lot of "oomph" (highly technical term there) to keep the engine turning at a higher speed.

I suspect in most cases, even with DFCO, you're better off going to neutral to allow the engine revs to be slower. (Not to mention, the drivetrain is a pretty inefficient way to turn the engine).

As you said, a scangauge will be the best tool to tell.

-Bob C.

Well that's kind of the beauty of the automatic trans. They're not "in gear or not" in most scenarios. Due to the way the torque converter works, there's a good chance that under coasting conditions the auto box has been told to remove pressure, allowing some engine/drivetrain seperation.

That's why on a lot of the american luxury cars from the 80's you could literally watch the RPM's drop off as you let off the gas. They weren't that great, as they didn't come back on the throttle nicely, but they were going for as quiet of a ride as possible. Modern auto transmissions exhibit the same phenomina. Letting of the gas you can watch the RPM's drop a good 500-1000RPM, maybe more in some cars. Do you really think the entire car is slowing down that fast? ;)

Obviously an auto is as economical as a manual, but they operate very differently. Let's not forget those facts when talking about manual driving methods used on an auto.

With my F250 on the straights, better to neutral coast on the P&Gs. Also better to neutral coast to the stop signs as much as possible, trying to time it so that you are under 35 mph before hitting the brakes, or going to drive for engine compression braking. I found that my diesel has too much compression braking for staying in Drive while P&G.

If I were going down steep hills for extended periods, then I'd go with staying in Drive and let the engine do the braking. If during this time you find yourself slowing down while going downhill, then I'd go back to neutral and effectively do Neutral-Drive P&G without the throttle. Diesels have much higher compression ratios than gassers, so the P&G is a tad different. Unless you can stay in Drive and coast a long ways, I'd stick with neutral coasting. My F250 can't do that.

With a diesel, you can let it slog as soon as you've got the transmission in lockup or are above the TC stall speed, so probably briskish acceleration at over 2000 rpm until you get up to TC lockup speed (usually around 45mph) is best, then let it loaf along just as fast as it needs to to stay in lockup.

Thanks for everyones input but i experience the same problem as his F250... my car slows way down if i dont put it into nuetral so im going to keep trying P&G with switching to neutral and see how i do on FE. I will try RPM matching cause i still feel wierd about having that boost in RPMs. So ill keep watching my FE and see if it can get me back up to my 35 or above range. I have a feelig this tank will be good its my first tank where i can actually try to hypermile it the whole time.

Also is there anything else that you have done metro to your diesel that has helped you or any other driving skills that i can try.

Again thanks for everyones help.

Thanks Jay for looking for me i didnt think they had it for me anyways... does the fact that it is an import matter about the laws for the scangauge port that is supposed to be required??

Might be more due to it being a diesel than an import, since the EPA regs were different and OBD-II was EPA driven.

OBDII was required on new cars and light duty trucks sold in the US for model years 1996 & newer. Some vehicles were compliant a year or 2 ahead of schedule, but being a 95 model it was not required.

-Jay

Your car might not unlock the TC on idle. My old toyota used to do that but the tracker doesn't. It'll stay locked even with the brakes pressed as long as it is above 36mph. I manually disengage the tc on the freeway and it gives me a bit more coasting before i have to hit the gas again.

This question has been asked many times. For more information than you've ever wanted, just do a little searching. When it's all said and done, MOST automatics are fine for neutral coasting. Some are good for coasting with the engine off, but most are not. Some are not good for coasting in neutral even with the engine on (my wife's Isuzu, for example; a transmission temperature indicator lights up).

Why so high? :( Mine goes down to 550, same as idling in Park.

QUOTE=BEEF;116232]depending on the year (1995, I know) your car might DFCO which makes it almost useless to shift into neutral. no gas is better than less gas.[/quote]

Rarely. Most vehicles lose more energy from slowing down than they save by not idling the engine. Sure, DFCO means no immediate fuel usage, but it slows the vehicle which then has to be re-accelerated later. Each car differs, but I suspect that most do better with neutral coasting in P&G than trying to P&DFCO.

Plus, just because car can DFCO doesn't mean that it does so immediately and dependably. There's a lot of variables involved in the computer's decision to DFCO, and they are different in each vehicle.

I have asked this before and I never got a really good answer. The best explanation is that the computer is trying to rev match somewhat based on vehicle speed.

-Jay

Yeah, it's some stupid fast idle built into the computer. The tracker regularly idles at 1100-1200 when in neutral on the freeway. I used to think the transmission wasn't completely disengaging but afterwards if i stop and go into park the idle jumps up to 1200 again and slowly starts to settle down.

On mine if I shift into N @ 60 MPH it falls from ~1,500 -1,600 to ~900 - 1,000. If I let it coast to a stop the RPM's slowly fall until I reach ~ 8 MPH then they drop to ~650 RPM.

-Jay

Stupid question but what does TC mean??
remember im new here so still dont know much yet lol

Torque Converter

-Jay

ok thanks man

Here is what I found that seems to provide my auto-tranny the best MPG, and especially for city driving.

The strategy I use is to work with the ECU computer and VVTi mechanism by getting to the "cruise speed" quickly. In other words, if the ECU thinks your still getting up to speed, the VVTi will not be set to economy/lean burn mode. So if for example the speed limit is 40 mph, I jump up to 42, then back off to 40...per the scan gauge, the MPG goes up to 33-35, then settles to 50 at 40 MPH. Once I settle to 40 MPH, the ECU issues a command to the VVTi to change the timing to result in lean-burn mode.

The problem with some styles of driving is that people are not mindful about get to cruise fast...often starting out too slow and too gradual up to cruise speed means wasting gasoline that otherwise does not have to be wasted. Of course jumping too fast to cruise can over consume gas too.

The Yaris has lean burn?

Yes, but not just the Yaris...most late model small cars that have variable valve timing have it...it works with DFCO, and fancy scripts that are programmed into the ECU.

can't believe no one has complimented you on your FE especially for such a big, heavy car.

sadly, you may very well be near your peak w/ this vehicle. but, hey, nicely done. with some help here, you may squeeze out a bit more.

morninggasser,

I notice in your garage that you are thinking of a WAI but haven't seen proof of it working. please see my gas log and the gas log of project84 (not sure of his vehicle name) it seems to work well with the little GM cars (cavs and saturns) there have been reports of it doing nothing. it all tepends on your computer and the sensors it uses (or so I have heard). maybe also consider a grill block as well.

your mileage has actually encouraged me. I was thinking of a yaris for a while but I am on the list for the smart. If I could get that mileage out of a yaris, I would probably rather do that. the waiting list for the smart is about a year and a half. I have about 8 mos to go. I may change my mind

*edit* I read it again and it said CAI not WAI. well anyway warm air intakes will help in FE.

With my auto trans the only thing I really do is shift into Neutral at longer red lights because I've watched the SGII and can see that in gear my car uses 0.45 GPH and in neutral it drops to 0.33 or around there.... other than that, I drive it extremely normally.

Only tip I can give is find out exactly where you enter your highest gear (4th gear) and drive the car at a speed that allows to be in 4th gear but not under much load. I enter 4th gear at 35mph when warmed, so I basically drive 35mph whenever possible, if the speed limit is 45, I'll slowly speed up to 45 then coast (in gear) to 35.

I heard a while back that in a higher gear you can use MORE throttle and get better FE than if you allow the car to downshift.... so even at 35mph I will sometimes use 30% throttle and still be over 25mpg climbing hills whereas if the car downshifts and I'm running 3,000 RPM in 3rd gear at 35mph the MPG drops to the teens.

Hope any of that helps! I tried P&G w/ neutral and found it to be a lot of effort, and after one tank of dedicated P&G I noticed no increase in FE. In my Saturn anyway, P&G w/ neutral doesn't yield much return, say at 40mph putting it in neutral reads 95mpg, in gear it will be roughly 82mpg. So, I assume it could help, but at the expense of added wear/tear on your transmission.

EDIT: Thanks for the shout-out BEEF! Yes, the WAI has helped my FE tremendously! I love mine, and it's just a basic rendering. To be more efficient it really needs to be insulated and sealed better. I might add though, whereas Saturns are notorious for oil burn issues related to the piston rings, my oil burn has drastically increased over the last 3k miles and I'm wondering if feeding the engine hot air could be some cause for it. Maybe/maybe not, like I said, these engines are notorious for it and I plan on re-ringing just as soon as I get one of my other projects on the road.

I tried the neutral coasting thing too. I saw a huge difference on the scangauge. I SHOULD have gotten 43MPG according to the scangauge for that tank and ended up with 36 or so. obviously something wasn't taken into account with the scangauge.

I think also it is a mixture of the fact that my eingine load is 25+ percent in neutral and the fact that my car will coast a long ways in gear. coasting in gear also nets me an engine load of single digits. the lowest I have seen is 7 percent.

I've been shutting the engine off @ lights where I know I'm going to be stopped for more than 30 seconds on my current tank. We'll see how it goes. SG doesn't seem to be reporting anything spectacular for the tank.

-Jay

I've sense decided that a CAI is not the way to go for FE. It may add a few HP's but even then, they will not be realized until high in the RPM range, and that is a range we hypermiler types stay away from. I agree, warmer air is the way to go for FE...As to the Smart car, well, I still can't get past it's tiny size in regard to accidents and such, regardless of how good the MPG is. Being a motorcycle rider too, I'm sure my issues with the Smart are irrational, but it's the way I feel about it.

Well, I guess all this work I've been putting into shutting the truck off @ lights is lost. I was cleaning the truck and when I was done I noticed my trip odometer reads zero. I also had disconnected the SG while cleaning the truck, so the tank data on my SG is reset too... :( It must have been good because its been 2 weeks since I've filled the tank and I still have 1/4 tank left. I guess I'll go out tomorrow and try to find some non ethanol blended gasoline and fillup. I also have plans to change the plug wires. I have a set of new OEM plug wires I bought @ the dealer last week. Its been raining for the past 2 days here so I haven't had a chance to put them in though.

-Jay

If you can check your gaslog and/or remember milestones (like say hitting 105k on the odo recently, something similar) you could probably figure out how many miles you have on this tank. I keep maintenance logs on my car and whenever I do something I record the mileage so at any given time I can figure out mileage on a tank from the most recent record compared to the odo.

I disconnect my SG everytime I park my car, too risky leaving it connected and on display for someone to swipe... maybe that's where all my inaccuracy is coming from w/ the tank readings?

Nothing remarkable happened on this tank. If I remember it had roughly 150 to 170 miles on it when the odometer was reset, and it had 120 miles on it when I reset again when I actually filled. I went anywhere between 250 and 270 miles on 19.3 gallons of fuel. On a side note I hope the station I filled at had E Zero gasoline. I was so far out in the woods that they didn't even have vapor recovery on the pumps.

-Jay