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?