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Old 06-29-2011, 01:53 PM   #1 (permalink)
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Default Lean Burn--w/Ultra-Gauge--Load+TPS<65=LB

Kind of a long post. Sorry. I am a Lean Burn (LB) novice. After warmer temps, rain stopped and fixed Herky jerky, I've finally discovered LB. I got a big boost in my understanding of it after getting an Ultra-Gauge with this great offer: UltraGauge Automotive Information Center and OBDII Scan Tool

I installed %Load, Eng Temp, Intake Temp, Throttle Position, First o2, and Second o2 (see photo). We all know that when second o2 goes to 0000, you are in LB.

This post is about the characteristics of LB in relation to the total of the Load and TPS readings when added together.

Obviously when you are stomping on the throttle (high TPS), you cannot get LB

Obviously when when you are climbing a hill (high %Load), you cannot get LB

What I notice is that if you add the two readings together (LOAD +TPS), if the total is less than 65, you will be in LB. In fact, I don't think you can avoid it.

Likewise, when the total reaches 130, you will lose LB. (These numbers are probably very general, and possibly other factors will show that they are not consistent.)

If you are cruising with a load of 70 and TPS of 22 (for a total of 92) and not in LB, you will not get to LB until you reduce the number to around 65. Once you get LB, you will stay in it until you reach the 130 number. I think it is unavoidable.

So here is a couple reasons this is important: Say you are not in LB, but your total is 92. There is no reason you should not drop the number temporarily to 65 or less, get in LB and then get back to 92. Once in LB you will maintain it until you hit 130 regardless of whether you have a steady foot or not.

If you think you should be in LB, but then look at the gauge and realize you are at 180, you are probably climbing a hill, have a headwind or two flat tires. You can drop to 65 (let off the gas) and get LB, but you already know you cannot keep it because it takes 180 with your current conditions. That has been a big help to me since I cannot always tell if I'm going up hill or bucking a headwind.

I have heard that you have to keep a steady throttle, but if you are between 65 & 130 you can move the throttle as much and as fast as you want and will stay in LB. (If you get kicked out of LB without seeing those numbers exceeded it is because the gauge is slow to respond).

I've tried it at speeds up to 80mph with intake temps between 70 and 85 degrees and the numbers seem constant. Of course you cannot maintain <130 at 80 mph unless you are going downhill or do other mods to reduce drag, but you can, in fact get LB at those speeds. The best mpg, of course will be at the lowest numbers, which means little load and throttle. These are just wild guesses, but I'm sure you can correlate the total number to mpg, so that possibly 125=65mpg and 50=150.

Steady foot rule: When you are in LB, which required you to get under 65(we're still talking about LOAD+TPS), you can maintain it through NOx purges even when cruising up to 130 (which I think is about max) if you don't change the TPS. So it will leave LB to do the purge, then if you have not increased TPS, it will go back to LB and the same number as before the purge. That is the only place I have found the steady foot rule to apply. If you lose LB, you have to go back to 65 briefly and then you can go right back to your previous number up to 130.

I have lots to learn, but I know LB has been confusing to most of us newbies. Keep experimenting!
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Last edited by kennysmith; 06-29-2011 at 04:11 PM.
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Old 06-29-2011, 02:05 PM   #2 (permalink)
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Super useful post, looking forward to testing this out.
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Old 06-30-2011, 12:55 PM   #3 (permalink)
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This seems like a complicated way of looking at it. Whenever I engage lean-burn I just adjust the throttle to where the FCD shows 100mpg and it will always go into lean-burn unless the car doesn't want to(too cold ambient temp, or engine under 155deg). Sometimes the car will refuse to go into lean-burn if you don't give it some heavier throttle for a few seconds and drop back down on the throttle again but most of the time 100mpg is all you need to do.

Mine will kick out over 32TPS, if load spikes too high(even if at 28TPS sometimes), or if you have high speed, at 75MPH if you are at 30TPS lean-burn doesn't hold. To reliably keep lean-burn up to 78MPH the max I could use for throttle was 26TPS even though the load value is around 80 and normally all signs would point to there being plenty of potential for more throttle.

Lean-burn also cuts out over a certain RPM too, 3000RPM or so if I remember right or about 55MPH in 3rd gear. 3rd gear will allow assist in lean-burn too which suprised me the first time I saw it but usually I don't want to use assist in lean-burn, I'd rather take it out of lean-burn and climb at 80-90LOD.
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Old 06-30-2011, 01:10 PM   #4 (permalink)
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Honestly, I just watch the FCD. I do watch my ScanGauge, but more just for correlation and general information. I don't even use the LBN XGauge anymore, since it's not telling me anything I don't already know - however TPS, load, ignition timing, coolant temp and intake air temp are interesting to monitor.

The only reason lean burn is tricky for new people is because..there's nothing else like it. Nobody is going to be used to an engine having two different states with completely different power characteristics. Most people's natural reaction when they feel the power loss associated with entering lean burn mode would be to press the pedal down, most likely in a fast, jerky motion - kicking you back out of LB. That's why the TPS sensor smoothing mod helps some people maintain LB, but the same thing can be accomplished by teaching yourself to move your foot only millimeters at a time.
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Old 06-30-2011, 02:48 PM   #5 (permalink)
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How do you use the intake temperature or ignition timing information? It's neat to know what they are but how do you use that information. I use the LBN value because sometimes the car will drop out of lean-burn when I'm at 125mpg descending a hill when I'm not looking but when looking at the FCD it is still in the lean-burn range so its good to see I'm still there but I wouldn't really need it because I can tell between the TPS, LOD, and FCD values if LBN is there or not but its not as easy as a simple glance.

After driving a 15 hour trip finishing yesterday evening, my foot still hurts this morning. I'm considering doing what a guy on the Japanese Insight forum did and installing a servo to set the TPS at a solid position so the foot can be taken off the gas, the ball of my foot, the ball of the big toe, and my knee don't seem to like 20 hours straight(done this before with only bathroom and meal stops) of driving.
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Old 06-30-2011, 03:02 PM   #6 (permalink)
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Quote:
Originally Posted by MN Driver View Post
This seems like a complicated way of looking at it. Whenever I engage lean-burn I just adjust the throttle to where the FCD shows 100mpg and it will always go into lean-burn unless the car doesn't want to(too cold ambient temp, or engine under 155deg).
You are probably right but it does not seem complicated to me. I'm not suggesting getting out a calculator, but when you take it to 100mpg and discover you cannot maintain LB. Do you try again in a few more miles? I would know by looking at those numbers that I will or will not be successful with LB.

With more experience, the gauge will probably become less important.

Quote:
Originally Posted by MN Driver View Post
Sometimes the car will refuse to go into lean-burn if you don't give it some heavier throttle for a few seconds and drop back down on the throttle again but most of the time 100mpg is all you need to do
Right, because you have to get that total number down to something like 65

You probably have a great feel for the car that I have not developed yet. I think the gauge will help me improve my skills.
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Old 06-30-2011, 03:16 PM   #7 (permalink)
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I agree, the gauge will help improve your skills.

Intake air temp, water temp, ignition timing.. they're not really useful as far as improving MPG goes, I just like having numbers to watch. If I had it my way, I'd have oil temperature and pressure along with exhaust gas temps for each cylinder and head temp too...

I did notice that sometimes I was not in lean burn when I thought I was, which was interesting.. but 80MPG is 80MPG? What would be the strategy in that situation? Try and lift your foot even more I guess?
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Old 06-30-2011, 04:52 PM   #8 (permalink)
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To add a little bit. Lately the weather has warmed up a lot, so I've been able to get the car in lean burn on demand.

I've seen values for O2 sensor #2 as low as 0.395 volts. I've noticed that timing advances to 30 - 35 degrees when in lean burn. It held in this range for most of the 15 mile trip home today with roughly 100F intake temp netting 110mpg (very minimal battery assist).


edit: meant degrees
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Old 06-30-2011, 05:12 PM   #9 (permalink)
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Does the Ultragauge present ignition timing as a percentage?

In the Scangauge it's a number, I assumed degrees of advance?

Now that I've been watching it more closely, I've seen from "-6" to "34" or so.
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Old 06-30-2011, 05:24 PM   #10 (permalink)
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kennysmith, the gauge will help you get there. I can't live without a way to monitor TPS and LOD. I also monitor coolant temp so I know when the car is ready for lean-burn but don't really need that because the 6 bars on the coolant gauge come up at 165 degrees so it's not critical. I monitor LBN to be sure I'm there but Eli does point out that it's pretty easy to tell, I agree but it's a good sanity glace-check when I'm not sure. I could live without a LBN x-gauge but it's nice to see for me at least.

I had some 120-130 degree intake temperatures yesterday driving through Illinois approaching Iowa, higher than I expected, got a 75.9mpg tank driving from St Louis home. I know that higher ambient helps with gas mileage and I suppose it is cool to look at but outside of physical modification of the intake towards the exhaust heat, I'm not going to have much use for it. I agree that it's interesting though, won't be my permanent gauge though but I'll leave coolant temp to watch it if I'm up to temp.

Eli, 80mpg in lean-burn can get a little more power out of the engine than not in lean-burn. Although at 80%+ load in lean-burn versus out of lean-burn I'm not seeing much difference. I did a three time comparison between using lean-burn and not using lean-burn when I'd need low 80's load in lean-burn (70-75MPG) and compared it to not operating in lean-burn and it made 66-68mpg difference on three runs versus 69-71mpg on the flat stretches that I was lucky to be in. Elevation monitored with a GPS. So lean-burn under higher load got just under 5mpg of gain in a non-scientific test for me in the situation I was in. Lean-burn helps a ton with a constant or lighter load but I'm not sure how much it helps beyond 85% load because it seems once I pass 80% load the MPG bar really moves to more consumpsion towards 90% load. Out of lean-burn 80% load gives about 50mpg and more performance, when I want to accelerate I usually use that if its enough performance for me rather than downshifting to 4th or 3rd and trying to snag lean-burn and then shift again. Saves effort and I don't really see much of a difference in MPG at all, I've switched my strategy on my highway commute after playing with that awhile. Less air pumping and an 80% load seems better than higher RPM and holding lean-burn, once I thought about it a bit, it seems to make more sense that lean-burn isn't always the most beneficial place to be. I've also adopted the 50mpg acceleration in 4th gear from 25mph to 40mph when I'm not in a hurry/nobody behind me, which is usually about 80% load out of lean-burn, and if the engine is cold, sometimes a little extra throttle to bring it to 80% load at 45mpg.
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