How to increase my mpg?? (98 civic LX 5-speed, AC always on)

[kennybobby]

Originally Posted by PaleMelanesian

I've been doing this for a few years now and I've tried all the combinations of load and rpm. 1500-2000 (sometimes 2200) and 80-90% load (13 psi MAP) is the best for mileage in these Hondas. On flat ground I can gain speed from as low as 1000 rpm, so 1500 is a conservative limit you can stretch and go lower if you like.

Hey PaleMel there is no messing with success and i have seen some of your impressive data and results in other posts, so you definitely know how to drive those hondas.

Let me ask you what is your typical acceleration times to get up to 40 mph and up to 60 mph from rest--in units of time in seconds or minutes such as the case may be...?

[PaleMelanesian]

Well, I usually don't hit 60 at all, since only one short stretch of my commute is even 55 mph limit. That's part of my secret: a good route.

I haven't measured, but it's probably about 15 sec to 40 mph. I'm still in the ballpark of other traffic while accelerating. 1st gear only to get rolling (5-10 ft), 2nd up to 10 mph, 3rd up to 20 mph, then 4th gear up to 40. I usually stop there and glide down to 20, then pulse back to 40. If I'm in a hurry I'll use 5th gear with 30-50 mph pulse-and-glide instead, and lose about 5% mpg.

Gauges to use (I have Scanguage which shows 4):

• Trip mpg - my most important gauge. Keep this moving up for the entire trip. If you must lose some on a hill, gain it back and more on the other side.
• Load - 85-90% load for acceleration is most efficient.
• water temp - for diagnostics
• volts - for diagnostics, especially with engine-off coasting and headlights
• instant mpg - if I had another spot, I'd show this one

[bestclimb]

I like the 6 guage screen page 1 to have MPG instant, %load, MPG AVE, UG volt, short trip MPG, DTE

page 2 gets the same except trip MPG instead of mpg ave and trip gallons used instead of UG voltage.

The next 2 pages have engine type guages rpm, temps and the like.

[California98Civic]

Originally Posted by PaleMelanesian

[*]Load - 85-90% load for acceleration is most efficient.

Whoa. You keep upping that number, no? I seem to recal you saying once that you thought over 80 was a waste. Then that you sought low mid 80s (I think), but suggesting as high as 90% is striking. I have to wonder if that would work on my very hilly route, where I unavoidably get stuck even at lights, on a steep incline 1-3 times per leg of my daily commute. Would you describe your experience more?

[PaleMelanesian]

I changed my approach since Sentra did his instrumented study on pulse loads. His best was 92%. I watched my Loop gauge more and determined that it's actually hard to hit Open Loop. I was initially fooled, because the first 3 seconds it really wants to go open loop. Once it gets past that, it locks in Closed Loop until well above 95 LOD. So now I target upper 80's to 90, trying not to pass 95. I *think* that change was one factor in my 90 mpg tank this summer, beating last summer's 88.

Oh, and I confirmed my 15-sec 0-40 acceleration.

[mattrich67]

That's very smart. I never thought about watching open and closed loop. If u can run in closed loop that would give the computer Ecu to run in its best cleanest fuel mixture possible.

These are great things to look for.

Thanks for the advise palemelanesian

[mattrich67]

Hey palemelanesian

So lets see here a couple things if I'm learning correctly

80-90% load as long as I am in closed loop
Short shifts (try to be under 2000 rpm)
Stay in closed loop

What about TPS % I hear a lot of different things?
What is a good WAI Temp or do you look at this?

Also I know people say coast in neautral to a light but what if I'm coming to a stop should I downshift and use my gears to slow down? Doesn't it go into lean mode if I do this?
Coasting in neutral just goes into reguluar idle fuel mixture reading doesn't it?

[California98Civic]

Originally Posted by PaleMelanesian

I changed my approach since Sentra did his instrumented study on pulse loads.

But Sentra drives an Xb, right? You're confident the BSFC map is similar, I take it.

[PaleMelanesian]

I used his testing as an incentive to try some new things. It seems to work for me, so I'm going to keep doing it the new way.

Matt:
TPS is related to LOD but less useful. To get 80% load at low rpm doesn't take much throttle opening at all, while at higher rpm you really have to bury the pedal. LOD is a constant target no matter what rpm you're running.

Engine braking is good IF you have to brake. If you can plan ahead and coast to a stop, that's better. If a light changes or a traffic event forces you to bleed off speed, engine braking is good. Above 1200 rpm, our cars shut off the fuel completely, letting the wheels drive the dead engine. When it gets below 1200 it turns the injectors back on to avoid stalling.

[serialk11r]

Hmmm 85% load...that's quite high!
It's hard to tell what load has the best BSFC, but most engines seem to be within 15% of peak efficiency by 50% load. I think this has to do with the fact that higher combustion pressure starts to be wasted after ~50%. More power offsets the proportionally higher friction at low load though, so peak efficiency comes at higher loads. I think any OBDII car keeps closed loop even at WOT below some engine speed, I know mine does.

I try to use 60-70% load to accelerate because it offers most of the efficiency but makes controlling acceleration and avoiding braking much easier. Additionally, when pulse and gliding, the longer pulse may consume a bit more fuel but I think it reduces the proportion of transient conditions (needing to rev the engine back up) and idle. I love slightly hilly highways because I can pulse up the incline at 50-60% load without building speed at all, and then drop into neutral down the hill and lose speed slowly. But most importantly the lower load makes it easier to drive since there's less power coming on. With my featherweight car and absurdly short gears this is especially an issue, although your Civics aren't much heavier! I ditched my spare for luggage space so I should be at 2175-2180lbs with full tank of gas.