Lean bank effect on MPG - Fuelly Forums

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Old 07-22-2008, 03:55 PM   #1
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Lean bank effect on MPG

My 98 3.8 Mustang has always had the check engine light on, but it has always said "Manufactor controlled auxillary emission". I was told this would mostly effect the car's pollution, and shouldn't effect mpg/fe. Well, the other day I scanned it just for the fun of it and I got 3 codes. The normal one, one that said Bank 1 too lean, and another that said Oxygen sensor bank 2 sensor 1 was faulty...

So, acouple questions. Is it true that the auxillary emissions isn't messing with my car too bad? What are the effects of a lean bank (yes, I got a new one, just need to install it)? And the faulty sensor is on the other bank, does this mean I have problems in both side.

If its worth anything, its also an automatic (booo) and has 130,000miles. All plugs and wires recently replaced. Only "performance" modifications are gt-cut off dual exhaust (this just takes the Gt's exhaust AFTER the cats and welds up), 25% underdrive pully, and Cobra wheels.
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Old 07-22-2008, 04:07 PM   #2
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Lean code could be vacuum leak, weak injector? Exhaust mod's will effect mileage and spark timeing.
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Old 07-22-2008, 06:25 PM   #3
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Lean code from an O2 sensor doesn't meant you're running lean, because they fail "lean", possibly means that side has been running rich if it has failed.

It's an auto... so try this, drive it harder.

Yup, I said that.

"grannying" Marvin gets me 20mpg. Setting off briskly, above 2000 RPM (Stall) and getting up to speed rapidly without mashing the gas so hard it holds it in gear, seems to help a lot, gets me hitting around the 23 avg you see there.

Set off like you mean it, (while keeping the back end planted of course) and lift right off and reapply at city/highway speed or whatever.

This is a lot to do with using the engine in a better efficiency range, both for accelerating and for getting to a cruise speed quickly and not wasting 10 mins trying to get 2mpg better sllllowwwwly accelerating up to speed looking at the scangauge, just get to speed quickly.
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Old 07-22-2008, 07:39 PM   #4
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I used to drive it hard, back when gas was 2$, and I only got 15mpg usually. Normal driving usually got me about 17-18, and now that Im doing more extreme driving techniques, I can get low 20's. I don't see how driving harder is going to get me higher mpg's....but maybe thats just me...

90% of my driving is light-city or "surburban" driving btw. On highway, I can get high 20's, but I never drive much on the highway. 2.79 gears help that..
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Old 07-23-2008, 04:04 AM   #5
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By driving hard, I don't mean stopping driving smart. The only reason that "acceleration is baaad mmmmkay" advice is bandied around is because 99% of the sheeple out there over-accelerate and need to brake again soon after. Judge your acceleration to a tee, never go faster than you have to, but get to your target speed ASAP, you don't need to be wasting 40% of your gas thrashing tranny fluid for any longer than you have to.
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Old 07-23-2008, 04:26 AM   #6
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Lowest possible vacuum reading, at lowest RPM, in highest practical gear.

Lowest vacuum= greatest percentage of atmospheric pressure in cylinder per power stroke= best efficiency.

Lowest RPM= fewer combustion strokes per unit of distance.

Highest practical gear means fewer combustion strokes per unit of distance, as long as you do not need a greater rate of acceleration.

That worked great in my non lean burn Del Sol, but the tactic is different in the VX, due to lean burn changing the BSFC map.

regards
gary
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Old 07-23-2008, 06:06 AM   #7
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I won't argue with that, my point is, with an auto you need to get into that range ASAP, because in slow acceleration below TC stall point you're only getting about 60% of your power to the road, the other 40% is lost in heat in the shear forces in the torque convertor. You're not only wasting gas, you're killing your fluid and shortening the life of the tranny. Modern electronic automatics also adjust to driving behaviour, accelerating slowly will get you a long drawn out shift where you're scrubbing the clutches of two gears at the same time, whereas accelerating more briskly should give you a cleaner/quicker shift. I'm not saying floor it, I'm not saying to test the adhesion limit of your tires at every stop sign, I'm saying give it about 30-50% throttle to take off, rather than trying to "ease it" up to speed with 10%. As soon as your going a steady speed, the TC will catch up and stop slipping so much and you'll only lose 10% vs 40% at typical city speeds, at fast city (40ish) or highway, your TC should lockup and you'll get 100% of your output to the road (neglecting frictional losses in the gearing)

About the only exception to this is if setting off down hill and you can basically coast up to speed.

A standard transmission you can let it slog up to speed, changing up at the minimum revs for the next gear, you get brief slippage in the clutch but get all your power moving you. Autos are different, so need to be driven different. If you have a robotised manual type automatic, then the manual strategy may work better, anything with a torque convertor accelerate more briskly.
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Old 07-23-2008, 07:18 AM   #8
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I agree with RW. Spending a lot of time and engine revolutions trying to mosey up to your speed isn't as effective in an automatic as just briskly getting up to speed. Get up to speed, get the acceleration over with so you can concentrate on cruising. The more open throttle reduces pumping losses, and the better acceleration leaves you in lower gears for less time. I can look at it different ways to support one strategy or the other, but real world results support the strategy described by RW.

You can also get some speed, back off the go pedal to encourage the next shift, then resume gassing it.

If you have tiptronic, paddle shifters, or any control of the gear selection where the transmission is obedient, the style will differ. I don't know if enough hypermilers have that kind of control to have a decent data set for figuring out the best strategy.
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Old 07-27-2008, 12:26 PM   #9
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I don't see how letting an automatic stay in a lower gear (such as 1st) is better than letting it shift as soon as possible. In my experience, I have gotten very good mileage when driving in such a way as to get the car to shift as soon as possible. I've never been able to get an automatic to quickly accelerate while preventing it from holding its gear which means I do have to gently accelerate in order to get better mileage.
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