Test on number 88 - Page 2 - Fuel Economy, Hypermiling, EcoModding News and Forum

MPGranger · 07-06-2012, 09:39 AM

my scangauge reports a LOD of about 20 while I am gliding, with AC on or the alternator going, or the lights on, or the fan running it gets up to the low 30s. So is there a way to zero my scangauge to read idle as LOD0?

Anyways idle out of gear wouldn't the engine still be doing some work? Moving the pistons, valves, sucking in air, oil and fuel pumps, and all the parasites on the timing belt. And wouldn't that work be getting down at a very inefficient load? Explaining why it takes 30 LOD to idle the engine and use AC, but 70 to have the tranny in gear and accelerate to highway speed.

NachtRitter · 07-06-2012, 02:44 PM

Is that what is meant by Tip #88? Light load = idle? I thought 'light load' meant something like driving in gear on a level road... in other words, running at the 'cruising' rpm, not at idle.

2000mc · 07-07-2012, 02:10 PM

this might also vary from vehicle to vehicle. for underpowered vehicles, or vehicles where running the a/c makes a noticeable difference in performance, there could be an indirect affect. i have about a half mile long steep hill on my commute right now, with the a/c on i cant maintain 4th gear up the hill. even hitting the base of the hill at 65 i drop under 40, and out of 4th gear, by the top. with the a/c off i can maintain speed up the hill. same applies to a variety of situations for me, cutting the a/c can either allow the trans to shift earlier, or hold a higher gear.

HilseeJ · 07-07-2012, 04:34 PM

There are other factors that might come into play to really skew these results.

For instance, in my car, when I have the A/C on it takes more pressure on the pedal to get up to the same speed as if the A/C were off.

With that said, the A/C almost forces me to drive slower and with less pressure on the throttle, thereby making it impossible to accurately judge exactly how much of a load it is putting on the engine.

MPGranger · 07-08-2012, 11:12 PM

Quote:

Originally Posted by HilseeJ

There are other factors that might come into play to really skew these results.

For instance, in my car, when I have the A/C on it takes more pressure on the pedal to get up to the same speed as if the A/C were off.

With that said, the A/C almost forces me to drive slower and with less pressure on the throttle, thereby making it impossible to accurately judge exactly how much of a load it is putting on the engine.

Do you have a scangauge or ultragauge? I can sit at 70LOD all day, pedal pressure varies. Going uphill and downhill are two very big variables. Also AC, which is why I started the thread, hoping someone already thought of this.

Fat Charlie · 07-09-2012, 10:00 AM

NachtRitter- Sorry, I was reading "light/DFCO" to mean "idle/engine braking" and "moderate/heavy" as "cruising/accelerating."

I do as little constant load cruising as possible, and with my hills that means almost none. About the only time that I'm not actively P&Ging is when my wife calls me. As terrain dictates I'll have light pulses, but my goal is to either be on or off.

I'm still new at this (just over a year) and the roads I live on don't lend themselves to refining my technique away from hard P&G. With my P&G mindset if I'm not putting a real load on it then I shouldn't be putting any load on it at all, and with that kind of operation I'll try to pulse the compressor along with the rest of the car.

NachtRitter · 07-09-2012, 01:41 PM

Not a problem... you thought it was one way & I thought it was another, but I don't think the correct answer has been provided yet (at least not in this thread).

In any case, whatever it is you actually are doing is certainly the right thing, based on the FE you are getting with the car you are driving, and that is really all that matters...

Fat Charlie · 07-09-2012, 04:03 PM

And that's why the "correct answer" is so vague!

Mustang Dave · 07-09-2012, 08:06 PM

It all depends on the driving conditions. I rarely use AC, except on road trips through/to hotter places. Last year on my road trip to southern California, I tried "P&G" with my AC. Kept the "recirculating" switch on. I tried to engage the compressor only on level or downhill stretches. Another method I tried this year was engaging the compressor only when instantaneous MPG on my ScanGauge was higher than Tank Average MPG on my Mustang's information display. If it gets too hot for comfort, AC stays on.