Target driving, what am I doing wrong?
 

Hey all,

My previous tank saw a decrease to 34.5mpg in my Saturn. For the past 2 tanks I tried to employ target driving aided by my vacuum gauge. Last tank I got 37.8mph in relatively bad weather. As noted, this last tank (have yet to update my log) showed 34.5(ish) mpg.

Seems to me that target driving isn't yielding better results than just using my cruise control. The method I use to target drive is to get up to 60mph and hold my foot steady so my vacuum gauges wanders as little as possible. On flat, 15in-hg gets me 60mph so I try to hold as close to 15 as possible no matter the hill or valleys.

Am I doing something wrong? I am under the assumption that target driving is "pick a throttle position and hold it". I don't let my speed dip below 55mph so some hills get an extra dose of the pedal to not hold up traffic.

On the flip side, when I use cruise, the vacuum gauge can swing as low 4in-hg going up hills and ~25in-hg on the down slope.

My commute doesn't have what many would call hills if they grew up around mountains, for all intents and purposes, Delaware is flat but the highway I use has A LOT of overpasses. I'm wondering if they just aren't big enough to notice a difference between steady pedal and steady speed...

Any ideas?

I wouldn't say you are doing anything wrong. Just learning what works and what doesn't.
I haven't transferred my vacuum gauge into my current vehicle but when I used it (more than the MPGuino) I always tried to get as much vacuum without loosing speed during the steady portions of the trip. I would get to highway speed and then back off the pedal, just a bit, to increase vacuum and reduce fuel. This was a dynamic process and always required me adjusting to the terrain. It is a subtle technique and takes practice to know when you have backed off too much and deceleration starts.

Edit: I never considered target to mean speed or throttle position. Just target minimal fuel usage.

That's "fixed/constant throttle" driving, not target driving.

The target you want for "target driving" is MPG feedback. If your target is "40 MPG", you adjust your foot to hold/exceed that consumption target (traffic permitting).

This thread may shed some light on things. It got quite detailed:

http://ecomodder.com/forum/showthrea...eed-27577.html

Don't you need magic to lift off a bit and still maintain speed?

No, you don't. You have to try it. This is the extra waste of fuel you save once you get used to the feedback of the gauge.
Anyone drive with a vacuum gauge that can back me up here?

Think of it this way. Going up hill, Full throttle, no acceleration. Then back off just until you maintain the climb at that speed. You just saved a bunch of wasted gas. Now apply this to flat driving but it is more subtle.

Metro: thanks for the link. That thread got a whole lot longer since I last read through it. And I'll spend some time on it tonight :)

I have just a vacuum gauge that swings from 0 to 30 so the slightest bit of foot movement reflects quite clearly on the gauge face. Yes, you can lift off every so slightly and see a change on the vacuum gauge with no change on the speedo. If using a boost/vac gauge there might not be enough vac. swing to see the subtle changes.

Bingo. Correlate this behavior with a MPGuino, fine tune your response behavior and actual fuel usage from the MPGuino at each vac position and you have the magic.

This is what I do anyway. Your Mileage May Vary

When you see a change in MPG with the same driving habits, look first at temperature, then at wind. I regularly drive a 60 mile route where I get anything from 28 to 42 MPG depending on temperature and wind. Over 40 MPG requires at least 80 degrees and a tailwind, while below zero with a headwind gets less than 30 MPG.

doviatt -

Isn't there a risk that that's just an illusion caused by the fact that you are using an extremely accurate
method to measure one thing, and at the same time an extremely inaccurate method
to measure the other?

Yep. A grand illusion. Like I said ..works for me.
http://ecomodder.com/forum/fe-graphs/graph2507.gif

All I'm saying is I use my vacuum gauge as my main visual feedback. I correlate this information with my MPGuino. The vacuum gauge is very accurate to measure vacuum in the system. Greater amounts of vacuum means least amount of fuel used (a balance of minimal air/fuel mixture). This is verified with the MPGuino. I always drove for least fuel used. What part of this is inaccurate?

Setting aside variables, which are out of your control, wind, temperature, traffic? It seems that your efforts have paid off. If you did not take the care to drive ECO your MPG would have been worse.

Use and manipulate the temperature values in the fuel consumption calculator and you will see the dramatic effects. Then move up the scale to show net wind speed over your hood. Theoretical as the numbers are it will show you how wind and temperature will eat up your mileage.

ssnsvibe09
I agree completely. The seasonal temperature drags show on my fuel chart. The weekly wind would be a painful reminder on my individual entries. It was very noticeable to drive in wind. The patterns here had me mostly driving in head winds on both legs of my commute during summer time. The times it was calm show up as my peak tanks. Still I always focus on minimal fuel regardless of wind and temp.

spacemanspiff
you are doing a great job. More practice with the elements in mind. The chart doesn't always go up, you just have to keep the average as high as possible.

Yes.

I tend to use target driving as a main technique, since most of my driving is highway.

So my average driving speed (given a constant target MPG) rises and falls with the seasons/temperature. Faster in summer, slower in winter.

Need more aero mods. :(

Your belief that you went exactly the same speed after lifting off a bit, as you would have without doing so! (My claim here is that you have gone slightly slower that you otherwise would have, you simply don't know it.)

A claim that your engine makes the same torque at the same turning speed with both less air and fuel is not believable, and it would take very rigorous testing to convince a reasonable person of this. Testing, that you have not done!

I agree with your statement. But, it is not my belief to be challenged.
I never said any of this. When did I imply the word exactly or claim same torque or turning speed? These are your words and completely out of context.

The topic of this thread is target. A target is not exact, it is something you shoot or aim for. Furthermore the target under discussion has nothing to do with speed.
The target is high MPG which can be correlated with vacuum readings, MPGuino readings, etc. Speed has nothing to do with this.

One of these days I need to invest in a MPGuino. I know its only 60(ish) dollars from the member on here but I am not motivated to stand out in the cold and hack into my engine wiring for the inputs...should have done it in the summer.

Filled up again with only 243 miles to the tank but I did a lot of puttering around looking at Christmas lights for about 3 hours. Tank was 34mpg (a new red bar on the graph :( damn holidays!). Rest of the tank was on cruise control but I think I'm going to give constant throttle another shot this week and see what happens.

This is the reason I haven't hooked mine up to my newest ride also. This is ok as you get lots of base line miles to improve upon once you have more input once you do actually get one.

What has the temperatures been like for your driving lately? Do you do extra warm up time in the mornings before you head out?

I have to say 48% over EPA numbers for your car is nothing to complain about. :)

With respect to going up hill and lifting off the throttle to a point where it does not impact speed is the lively discussion at the moment.

We the eco drivers will not mat the throttle to accelerate up a hill. There is an instaneous torque/ horsepower limit at any engine speed where acceleration is not possible. Opening up the throttle beyond that point is only pouring fuel through the engine without benefit as the ECU will likely go into open loop mode on the A/F management and run rich.

Take a look at the next guy that is passing you on the hill and watch him lean ahead in his seat as he tries to "will" the car faster.... he already has it matted. might actually see black smoke....

My commute is almost all highway and the baseline that this site uses is the combined rating. The car is rated at 22/32/26 for city, highway and combined so I'm happy to be beating the highway numbers running around town but like all of us, I'd rather be doing better. Temps here are swinging quite wildly; teens at night high 40s during the day but some days staying in the low 30s. If there is frost on my windshield in the morning I start the car, scrape off the windows and then head out for work. Probably doesn't take more than a couple minutes and I like to give it some time to circulate the oil a little before heading out. With the cold mornings I am on the highway before the car reaches operating temp, in the summer I'm at operating temp by the time I exit my development :rolleyes:

Just have to keep at it I guess. I'm going to try to steady throttle this tank of gas and see I can do. If it's low again, I'll switch back to CC set to 60mph like I had be doing since I signed up here. Lots of little things I want to do still like sealing around the headlights and the hood gaps; just never got to them in the summer and glue won't stick very well in the cold...