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Old 06-26-2009, 04:23 PM   #41 (permalink)
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There are only a few reasons engines will intentionally run rich. Most of those occur when something is broken and the engine is trying to cool itself, but one occurs somewhat regularly.

If an engine can burn lean and it kicks back into stoich or rich or if its running stoich and it kicks into rich its doing it because cat temps are dropping. Cats are very simple, think bee honeycomb coated in expensive exotic materials. Its a very tight mesh hex comb because that traps fuel deposits against the materials that are very hot. . .fuel heat. . .fire. This removes the HCs the exotics are to remove other noxious compounds. If it for regulations cats could run as cool as you wanted, but the epa dictates that the cat operate at x temperature to make sure all HCs get consumed(even if there are 0 HCs. . .)

I don't think its so much the EPA is corrupt. . .more just misguided entirely. To avoid thread jacking I'll just say they don't understand necessary evils and ban the least of all evil options(R-12 for example) just because its most prevalent and causes eco damage. . .(134 does more, uses more fuel and does a crappy job).

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Old 07-03-2009, 03:38 PM   #42 (permalink)
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Bruce I think I have an answer for your speed limit issue.

If your trying to go lean it can only go lean with a limited volume of air. Otherwise it overheats. The throttle position is the first safety net to control this but I think you mentioned even that fluctuates a little. The second net is the RPM and I think the third is a combo of one and two.

The engine can handle the extra cooling needed to perform lean at around 16:1 with limited amounts of air but as you increase the AFR or the volume of air the radiator won't be able to keep up.

In order to protect itself the ECU kicks out of LB in order to cool the engine back down. I predict if the conditions just barely meet LB(coolest possible AIT) you can rev up a little higher than you can when its well inside of established boundaries.

If you bumped radiator pumps to a faster setting built in an internal resevoir(so you could flow maybe a 2 gallons of coolant and the coolant had time to reach ambient temperatures before it gets cycled back into the engine) and enlarged your radiator as well as added an oil cooler for the engine I think you could probably squeak a good deal more revs before kicking LB out. Maybe not. . . The ECU could be hardwire programmed not to allow input conditions from the driver opposed to limiting based on output conditions from sensors.
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Old 07-03-2009, 11:39 PM   #43 (permalink)
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Thanks theunchosen.
I think there's good sense in your notes.

It's pretty odd really - LB causes the cat to cool off and apparently causes the block to heat up. I'd assumed the hotter lean combustion temps were just local in the cylinder and the cooling system would keep the rest steady at the usual temp. But maybe not, if it runs very lean at wider throttle.

A couple weeks ago I took off all the lower grill blocks and only kept the full upper grill block I'd just built. In warm weather it's been mostly doing LB with no issues. In cool or rain it doesn't want to stay in LB.

Left side has a/c condenser, with cat and engine behind that. Right side has radiator, and tranny behind that.

I'm thinking, restore most of the blocking on the side where the cat is. Keep the cat warm. I'm sure there's a temp sensor inside an oxy sensor that talks to the ECU. In summer I need to leave a bit of air path open there because the a/c condenser is on that side, it needs some air flow.

And, in consideration of what you wrote, keep the air path on the other side - where the radiator is - open. So the rad can keep the engine cool when it gets hot in LB.

Still I have to say, just going from recollection, I think it mostly is cranky about LB in cooler or wet weather. I can test if blocking up the cat's cooling air flow gets me more LB.

Thanks!
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Old 07-04-2009, 12:00 AM   #44 (permalink)
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Heat shield just around the cat. It's only 3 inches wide by 4 inches long or so on the HX A small aluminum plate with mylar on the other side with a concave surface facing the engine ought to be enough to keep it toasty. I would space it just a little bit from the cat itself(the heat shield) it also keeps air flow up around the engine and the exhausts to keep EGTs and block temps down.
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Old 07-09-2009, 08:02 PM   #45 (permalink)
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The a/c fan is pretty close to the cat's cover shell. I think that anything put over that would block the air flow out of the fan. If I was willing + able I suppose I could put a pusher fan in front of the a/c condenser instead of the rear puller but I'm not ready to undertake that job.

It's been running very nicely though. Lean burn just about any time I want.

I did put a full block over all grill openings on the cat side of the car, and in the center portion of the grill also. The only part that's open is what's to the right of the license plate in the lower grill. Upper grill is fully blocked with a smooth panel.

Recently I adjusted the valves and the ignition timing. Timing had been set for maximum advance - not good. Adjusting it by timing light still left plenty of ping so I did trial and error to get it to clean up. I think I finally got it right today. Today's fillup was nearly 46 mpg and it looks like the next tank might be better than that.
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Old 06-18-2011, 02:17 PM   #46 (permalink)
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This is an interesting topic, I also have a lean-burn honda.
It's not the same engine as they use in the States, I'm from the Netherlands so I have a europian modell with a D15Z6 lean-burn engine.

I'm also traying to figure out, which sensor's and which readings are necessary to engage lean-burn.

-TPS signal 20% till 32% load.
-IAT above 5*Celcius
-ECT (coolend temp sensor) temp??? (Think above the warm-up mode from de IAC)
-Gear sensor???? (if there is such a thing in ower car) in 1st or 2nd gear even in the right rev and load range LB doesn't activate.
-RPM sensor, till 3000rpm but as stated above to low rpm disangages LB to but I think its lower than 2400rpm about 1750rpm
-RPM fluctuation sensor (located near the crank shaft), (instead of a wideband lambda sensor used in the d15z1).

-Probably MAP sensor
-There is no knock sensor in the d15z6
-Don't know about a Cat temp sensor, looked for one but couldn't find it.


To accomplish sustainable lean-burn, there has the be some sort of temprature control.
This is done throught the use of EGR.
The EGR exhaust fumes in de d-series honda come directly thought a hole in the exhaust port of the (thought) 1st cilinder.
This is the reason why the block warms up and the catalitic converter cools down.
I know that alot off lambda sensors need heat, and have internal heat coils.
That maybe a reason why its deactivates lean-burn, to warm up the lambda sensor.

What i found remarkeble is that after accelerating, thus being out of LB, you don't enter LB very fast, but you can trigger it by giving it a short hit bit of extra load!?! and then lift of the throttle again.

Solution?:
I heard of slowing/altering the TPS sensor, I do think it helps to stay in lean burn but also delays fuel shut-off while decelerating and maybe dangerous for emerencies.

Has I wrote in the tread below, I think a "CAI"(after IAT) wouldt help to stay in lean burn till a certain point.
Becouse then you don't to give such alot of load and thus staying well below TPS 32%.
http://ecomodder.com/forum/showthrea...hx-8784-5.html
Has you probably know the IAT is located in the rubber inlet hose about 3inch infront of the throttle valve.
So Inlet manifold tempretures aren't measured directly.
This allows us to cool the intake manifold has much as possible, before freezing the fuel.
You only got to make a warm inlet for the warm-up period, making the evaporating pressure of the fuel less.

One could short cicuit the coolent lines throught the throttle body.
But the biggist heat source while in lean-burn is the EGR gasses.
I'm thinking of relocating the EGR inlet, from the exhaust valve hole to after the lambda or cat, making it possible to externaly cool the EGR gasses and prefend LB deactivation for warming the lambda.
What I saw while looking at the inlet and head, is that there runs a coolend tube/hole next to the EGR in the block, thus cooling it a bit.

Last edited by beer; 06-18-2011 at 03:08 PM..
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Old 06-27-2011, 10:01 PM   #47 (permalink)
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I dream of owning a learn burn car one day.
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Old 03-07-2012, 06:50 PM   #48 (permalink)
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lean burn FTW

Got to learn more about it
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Old 03-07-2012, 08:45 PM   #49 (permalink)
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not trying to hijack the thread, but what do you guys think about a highly efficient 6 stroke, direct injection, variable valve timing, lean burn engine? Once I finish my current project, I planned on building an engine to try this out on.
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Old 03-12-2012, 05:27 PM   #50 (permalink)
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Lean burn all the way? Not. I had Chrysler lean burn car and embarrassing experience with it until I swapped nonfeedback carb and distributor with vacuum advance it it. Lean burn all the way? ------------Noooooooooooooooooooooooo.

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