Lean Burn all the way!
 

Ever since acquiring my SG my main effort with the HX has been to keep it in Lean Burn as much as possible when on the highway (I mostly drive on limited access roads, usually 50-60 mi each way to work).

Today with temps around 60 and the wai pulling intake air around 85-87 deg. F, it drove like a champ. Lean Burn all the way.

Went into lean burn promptly after about 1.5-2 miles of highway cruise, and stayed in LB as long as I didn't go past its usual throttle position limit of 32 TPS on the SG (which takes it into open loop operation). Even after exceeding TPS 32 or after a downhill idling coast, it went right back into LB when asked to. Also went right back into LB after a couple nearly-full-throttle accelerations to 75 in 3rd gear. It has tall gearing.

I expect 50 mpg and better in the near future.

I currently have the drivers side grill fully blocked; that's where the cat converter and a/c condenser are. I'm pretty sure that keeping the cat warm counts for a lot on this car. I've gotten occasional CEL's ref. cat, and LB status does seem to respond to heating up the cat with fuel and/or grill block.

Passenger side has the radiator; it's maybe 30% blocked at these outside temps. It seems to kick out of LB if coolant goes to 186 so I can't choke off the radiator's air flow.

Great news. I've always really wondered what an HX can do. It seems like a lot of owners get high 30s but I know the car can do so much more.

Sounds like a good commute. Remind me again how you're monitoring lean burn?

How long to the next fill-up? Please post back here so we know the actual outcome.

I have another approx. 200 miles left on this tank. I'm also temporarily off work awaiting a contract extension and also a new contract, so it could be a while to the next fillup.

I monitor Lean Burn status on the ScanGauge. Here's how to program it. Of course the procedure makes no sense if you don't have a SG or you don't have it's manual that gives you the basics of programming its X-Gauge options. Given those basics, one can do this.

TXD: 686AF10115
RXF: 044105150000
RXD: 2808
MTH: 000100020000
NAM: LBN

and save.

If the value for LBN = 0 you are in lean burn.

here's what I monitor on the SG
Coolant Temp - - - - - - - - - - - - Throttle Position
(due to grill block) - - - - - - - - -(LB kicks out at 32 TPS)

MPG or Intake Temp - - - - - - - - Lean Burn Status
(cold intake kills LB)

Def cool how you programed the SG to read lean burn :thumbup:

Thanks but I can only take credit for following the written notes. They're from a post by a MrChoi on another message board.

:thumbup:

Lean burn power FTW

I'm really not familiar with the SG at all, is there anyway you can actually measure you Burn ratio(stoich 14.7 what is your getting?)? I guess if you coudl measure the air flow and the fuel injected you could. . .?

I just keep tabs at fillups

I have a wideband O2 sensor and display that I bought for tuning purposes, it displays 10:1 up to 20:1 AFR's.
You have to have an extra O2 bung welded into your exhaust, the display can just plug into the cigarette lighter.
Expect to spend ~$200 though unless you get lucky and find a used one.
You can also tap into the right wires at the ecu and get a voltage readout at the stock sensor that you should be able to convert to approx AFR if you do some research.
There 02 sensor should have a heater wire, ground, + constant, and + variable(O2 reading).

RPMs Requirement: 2400+ (for Lean Burn)
 

Eureka. HX Lean Burn apparently requires 2400+ RPM

Sometimes I miss the most obvious things... In this case, in my search to learn the requirements for lean burn in the HX, I missed rpms.

2400 rpm and higher, to be specific. Just over 2500 on my dash tach but 2400+ on the ScanGauge. Or, in fifth gear, over 65 mph (on dash speedo). I've seen LB in lower gears so road speed isn't the requirement, it's rpms.

Below those levels, lean burn is iffy at best. I'm sure I've seen LB below 2400 rpm but at least in tonight's conditions that was the requirement.

Tonight, in conditions apparently perfect for Lean Burn, my '97 HX would not stay in lean burn and would go in only when it's "mind of it's own" decided to. Having noticed that increased speed sometimes helps, I brought it up over 65, and voila! Lean Burn. Next, I carefully monitored rpms and road speed to deduce what I wrote above.

OK, the other things I've written in the past still hold (notes below). But it seems they have an additional requirement, namely, 2400 rpm or better. Of course, attempting to go into LB at say 2410 rpm is probably a losing proposition because if you accelerate up to 2410, as soon as you let up on the throttle for the necessary TPS 20 or less, you'll lose rpm and will be below 2400, so no LB. Aside from that caveat, I seem pretty confident in this.

The other requirements:
TPS (throttle position) of 20 or less (as shown on SG) to enter LB. TPS over 31-32 will end LB. No air blowing on the cat converter - my grill is thoroughly blocked aside from the four segments in passenger side lower grill opening. Wet weather seems to reduce possibility of lean burn, but maybe that's due to the fact that I rarely drive over 65 if it's raining!

One other caveat. YMMV. I suspect my cat converter may not be functioning optimally, as I occasionally get a CEL with a code that references cat function. So it's possible that with a perfectly functioning cat the requirements for lean burn might be more lenient.

I think there's something else going on here:
Car is currently running on 89 octane due to good wife believing she heard knocking. "OK Honey, I will put in only 89 octane till we figure out what the noise is".

Edit:
I think the higher octane is enabling greater ign. advance - and the fuel management map limits lean burn when there's more advance.

Higher octane will allow more advance, as the knock sensor dynamically contributes to advance settings. I suspect the ECU is programmed to disallow lean burn when advance exceeds some predetermined amount. Of course ECU is designed for 87 octane but with 89 the advance will be more than generally expected so lean burn is disallowed more often.

This would fit with less lean burn occurring in wet conditions - the water 'mist' in the intake air also reduces knock, allows more advance, and so probably places more restrictions on lean burn.

I'll be testing for this by using different octanes, but at ~475 miles/tank that testing will not be rapid.

So what factors contribute to lean burn? I have a CA model HX and I drive 70 miles round trip, lately since the NBA finals have started I've driven a bit faster to get home :)

But normally I am driving at 60-65 a 17-20 Throttle position. Best tank I've got was 42mpg with tires at 44psi. Still haven't had a chance to drive 60-65, no ac, for the whole tank.

The knock sensor will not advance ignition timing. A properly running engine will have no difference in spark advance between 87 and 89 octane fuel (provided the engine is designed to run on 87). The knock sensor is there to pull spark IF and ONLY IF it detects knock, to avoid damage to the engine in the event of something going wrong, such as bad fuel. If the engine were to continue advancing spark until it detected knock, and the knock sensor were broken... every failed knock sensor would result in a destroyed motor. That being said, if there is something wrong with the car, and it's knocking, i could very clearly see there being a rule saying, In the event of timing retardation due to knock, do NOT enter lean burn, as lean burn would greatly aggravate knock.

Further developments.
The car now will enter and stay in lean burn well below 65 mph.

The morning of June 8 I heard an exhaust leak up front, so I took it to Monro Muffler (franchise). Cat converter/exhaust manifold combination was OK but they replaced everything behind it. I also removed all the remaining lower grill block which was mostly on the cat converter side of the grill as I didn't want them to get in a twist over it.

With those changes, it now goes into LB and stays there just as I'd earlier worked out. Warmed up, TPS below 20. Will stay in LB unless TPS goes over 32.

I don't know yet if I'll need to replace the lower cat-side grill block when the weather gets cold or rainy. We'll see. For now I'm a very happy camper because it will run in LB at the drop of a hat. Unfortunately I'll never know if the cure was the exhaust fix or the removal of the grill block.

Sorry for the red herring info earlier.

I don't think the grill block would effect it. I would re-install the block.

There was probably a problem in that the EGR not functioning properly due to the exhuast leak. This might throw the fuel trims way out of line, (not enough exhuast in the intake air), throw the check engine light you were seeing, and prevent lean burn.

Mind you, that's all supposition from a computer engineer, not an automotive one... :) YMMV, etc...

Throw the grill block back in,and see what happens? Only costs you a bit of time, and some skinned knuckles worst case?

-Steve

Do you have the LB gauge set up on your ScanGauge? I'm assuming you have one as you're reporting TPS data. Right now I'm seeing LB anywhere between 55-75 mph. Probably higher, as long as you don't exceed 32 TPS. I never tried because I hate those on-the-spot interviews with the men in blue.

If your tires are sound and rated 44 psi or better, consider putting them up to 50, cold.

As for a/c, I've (sometimes) been switching it on and off manually, on the a/c button. I leave the temp slider at max cold and switch the compressor off when it gets pretty cold and back on again when the chill is gone. (apologies to BB King) hear him

not enough exhaust in the intake air??
Hmm. Does it have EGR that pulls from post-cat converter?

Even aside from the intake air bit, I'm sure that the leak just aft of the cat messed up the O2 readings. And I bet that leak was building for a while and finally became clearly audible.

OK, I have to admit to CRS syndrome; I'm now past 55 and I don't mean mph. I"m PRETTY sure I ran it for about 40 mi. with the grill block back in and had trouble keeping LB. But I will put the lower grill block in for tomorrow's 60-mile ride up to work and we'll see how it goes. No inconvenience at all - it's sections of foam pipe insulation bundled together to fit the grill openings. Easily removable and reinstallable.

I am glad to see this thread, I am wanting to talk to more people with CA spec hx's. Since I have installed my mpguino, Ive been watching my instant mpgs and my gallon/hour reading to try to get a better feel for whether or not I am in LB.

Before I had any instrumentation I got two or three tanks at 49 mpg average. Now, my mileage has gotten worse. I try to maintain the best instant mpgs all the time and in the end I think it is killing me. So now lately I have been sucking it on my instant mpgs while I accelerate for the sake of getting to cruising speed a bit quicker and holding a much higher cruising instant mpg.

Help me out, what am I doing wrong?

I have that $20 digital voltmeter kit from australia in the mail, that will let me watch lean burn a LOT better.

Also, just FYI my car has a "faulty" ECU that throws a code occasionally similarly to yours Bruce, except mine is for a 02 sensor reading slowly. There is a TSB for it and apparently the ecu just needs to be replaced with an updated version. Its like $600 so I just deal with the light coming on every 1 to 2 months.

Shoot, I wish I knew! The occasional ECU code sounds scary. Hopefully that's not what's messing things up. $600 - ulp!

It's very sensitive to throttle position which I watch constantly on the ScanGauge. Without that monitoring I'm sure LB would happen much less often. When needed I can also watch intake air temp, coolant temp, and other stuff that might not matter.

Tell me about the $20 voltmeter kit. Link??

You may know from other posts that I'm watching LB on the ScanGauge. That costs >$20 though. And it only recognizes LB for a gauge readout but not for its mpg calculations. If the MPGuino was as easy to install as the SG I would have one already. I just don't feel like hacking into the wiring on this beast right now.

CRS syndrome?

I'm was thinking the leak was dropping exhuast pressure, and this was causing EGR action to slow down, and throw things off. Didn't think about a post cat O2 sensor. Perhaps I should just stick to code? :P

Either way, try 'er and see!

CRS = Can't Remember S**t
Happens to all of us eventually.

Yeah you're right - any leak in the exhaust certainly has the potential to mess up fuel management. I didn't think about EGR foul-up but that's a possibility. The main O2 is in (just before??) the cat and the 2nd one is just after it, or at the back end of the cat. I'm pretty sure the job of 2nd O2 is to verify the final exhaust is clean enough.

The 1st and 2nd O2 sensors work in comparison with each other to make sure the catalyst is working properly.

Here is the link

http://ecomodder.com/forum/showthrea...nsor-5204.html

It basically watches what the 02 sensor is reading and lights up according LEDs on your dash. Its a non numeric readout but its no matter to me.

Bruce, I also noticed the same thing with my car, it seems like sometimes LB will not engage below 2200, 2300, whatever. What a mystery this lean burn is! I understand that you don't want to get mixed up in the wiring and stuff but it is really quite simple! I am not an electrician, Ive only soldered stuff on cars a handful of times and I almost always ask somebody more knowledgeable to explain how to do stuff first. But this kit is really not hard to install. I am glad that I got the MPGuino because it reads accurate instant MPGs, whereas the scan gauge measures instant MPGs assuming a constant air to fuel ratio. But whatever.

I have been getting so frustrated with this LB not working the way I wish it would, Im going to try a couple of things first but I am considering getting illegal and buying a $30 non CA ecm. Its gas mileage versus the EPA!!!!!

Right now I have a PVC pipe hardware store intake thing goin on... hey, it was cheap. I just had my buddy crush bend a 2.5" exhaust pipe for free. Im gonna see if the warmer air through the intake is what it takes. And beyond that, a grill block, and undertray. Aero mods mean less throttle needed. yipee.

Thanks, LeanBurninating.

Now for tonight's installment in the quest to understand the HX lean burn logic:

The switch to not allowing lean burn under 64/65 mph is determined by a distance clock. Yup. A simple counter that kicks in after about 23 miles or so (~37 km). Keying off the ignition for 10 seconds reset the counter, after which full lean burn was again available. Hopefully only a brief shutdown is needed; for this test I wanted to be sure to be over 10 sec. to try to ensure a full reboot.

As I watched for LB failure (that is, losing it below 65 mph) I paid close attention to engine and intake air temps and they were moderate. ECT was 182 deg. F which is where it always stabilizes unless it's over about 75-80 degrees outside, or if I'm running the cabin heat. Intake air was about 75 deg. which is about as moderate as you could get. Nothing else going on that I noted. Keying off the ignition and bump starting it brought it back to full lean burn operation - as long as I kept the throttle below about 30 tps, it would maintain LB down below 55 mph in 5th. After a restart it does require a mile or two of driving before LB will kick in, but I can deal with that.

So now I want to find how to wire an ignition cutout. My regular commute is about 60 miles so it would be nice to be able to maintain lean burn. Maybe the easiest is to find the power wire to the ECU circuit at the ign. switch and put an intermittent-off switch in that line, either before or after the ign. switch.

That is really interesting... I wonder why it works that way? Why would it kick out? So you watch it kick out every time at 23 miles? How many times has it done this for you? Have you seen it on more than one route? Maybe its the driving conditions of your commute?

For CA spec cars, supposedly it kicks out when the NOX gasses build up to a certain level, so the motor can burn out the NOX gases. I could be wrong. I don't think that non CA hx's do this.

I just got my air fuel ratio toy in the mail today, I hope to get it hooked up soon to join in the game.

Thanks for posting up, Bruce.

Happened the last time I had it on a long run also, semewhere between 20-30 miles into the trip - I wasn't paying close attention to the distance yet. I wasn't thinking mileage, I was thinking cat temp and engine temp etc. Tonight it was very cool out; I figured I'd take a run and see what happened. Tomorrow I'll drive 60 mi. to work. You can bet that I'm going to pay close attention to exactly when I lose LB.

Since my last post I've had the HX out for two 60-mile commute runs plus other driving.
On one long run, it went into Lean Burn stayed there.
On some of the other trips, it developed the "rpm sensitivity" I described.
I wasn't able to identify yet what causes it.

Anyway, the 23-mile thing is not consistent. RPM-restricted Lean Burn has kicked in at other distances that were further than 23 miles.

In the time since the last post I had a shop do an injector/valve/upper cylinder cleaning. Because my good wife heard "ping" - I want to get all the carbon cleaned out to help eliminate early detonation. They put the last of the cleaner into the tank so that fuel is not standard fuel - I think I can smell the cleaner in the exhaust.

I'll be driving again the next three workdays so I'll see how it goes.

May I recommend sea foam to you.

I can't give you professional advice for it, but I would definitely look into it. Its a clear liquid in a can, you can get it at kragen/schucks and you can use it to clean out deposits.

You pop off the vacuum line for your fuel pressure regulator and literally suck this stuff into your vacuum system. While your engine is idling you suck up a prescribed amount, you have to let the line sip at it as dunking the line will stall the motor, and then when you have enough sucked into your engine you then dunk the line and stall the motor and leave your motor off with all of this stuff in the engine, it will be all over your valves, pistons, heads, intake runners, etc.

Then after letting it sit when you start it back up it will burn out all your carbon deposits. Just drive it hard till all the smoke stops coming out. The more smoke, the more carbon you are burning out. I know that this works because the first time I did this I made tons of smoke and the next times were less and less.

Use the vacuum line from the brake booster... it fits into the top of the can, usually, and make sure you dump out 2/3 of the can into something else first. (you only need 1/3 of the can in your engine).

Fuel based "engine cleaners" do not work, simply because there are already so many detergents and additives in your fuel that adding a little more is like adding soap to the suds on your hands.

The other reason they don't work is because so little fuel gets injected at such a high temperature into your engine, that it's nearly completely vaporous by the time it actually gets to the combustion chambers... vaporous cleaning supplies do next to nothing, unless they're steam.

Another thing you can do to clean out your engine (that actually works) is just a light mist of water into the intake pipe, before the filter. It's just like steam cleaning, and will eventually loosen any crap that's built up in your engine.

Thanks guys.
I previously gave it a seafoam treatment, twice. A couple months ago. Instead of sucking it in via a vacuum hose I poured it in slowly, into the big corrugated rubber air intake hose - right after the air cleaner which I temporarily disconnected. I've used the vacuum-hose method before on my Volvo 240, this method seemed to work the same - made lots of smoke and needed extra rpms to keep the idle going. And, lots of smoke and junk when restarting afterwards. I'm sure I cleaned out lots of junk that way, myself.

The shop used a cleaner they sucked into the engine via a vacuum line. Also supposedly produced lots of smoke/junk when restarting afterwards - but I wasn't there for that. Seems to run better now though.

The first video at http://ecomodder.com/forum/showthrea...ions-8629.html mentions that the computer will enrich the mixture now and then to regenerate the catalytic converter. This behavior would obviously involve exiting lean burn. I'm not sure if your cat is of the same type, but if so, you'll want to decide whether the occasional fuel dump is required to keep your cat alive. Find out, because IIRC, your cat costs buckets of ducats.

I'll watch this thread with interest, since I hope to join the lean burn club soon.

Robert,
That's probably happening. I sure wish there were a screen to tell you what's going on, or a manual. Anyway, as long as I can keep it from happening often, I'm pleased.

Here's hoping you do join the Lean Burn club soon!

There's a thread currently on honda-tech.com that you should look at.
better gas mileage out of an eg - Honda-Tech
Near the bottom of the first page there's a post by member HXor. The thread is now up to 4 pages and includes a lively discussion of lean burn and FE driving. IMHO the information here at EcoModder is better, but it's an interesting discussion nonetheless.

It wouldn't keep the at alive in terms of the cat being destroyed. . .it keeps the cat active.

I think I made a note of this, but maybe it was on another thread. To get by EPA you can't have any arguments like "well the car is really not producing any HCs in this mode so it doesn't need a cat during this. . ."

They slap you with a fail and send you packing. So Honda had to ensure that the cat stays up at operating temps. During LB EGTs are higher but the cat is going to be acting like a huge exhaust radiator. Its a big metal box with lots of wind exposure and no HCs are getting burnt inside so its surviving in the operating range only by the higher EGTs. To ensure to the EPA's satisfaction that the cat stays hot enough to burn the one in a million HC that slips through the engine unburnt it has to kick out of lean burn to reheat the cat.

It won't damage the cat to run at low temperature(assuming there are no HCs in the exhaust flow, otherwise its going to get covered in soot).

I've heard(can anyone verify) that the base problem with much of this technology is that our EPA is corrupt and emissions limits here are based on emissions per X amount of fuel used, not per mile. So a big guzzling SUV getting 10mpg can emit pollutants at the same percentage per unit of fuel consumed, but if the 35mpg car emits 1.01 times the pollutants of the SUV, but overall it's less than a 1/3rd of the total emissions per mile of the SUV, it still fails.
Regarding the lean burn, the OBD-2 system uses the knock sensor to keep lean burn at the edge of detonation, instead of the wideband o2 sensor like the OBD-1 VX. Fuel is pulled back to the brink of detonation, not the timing.
The perimeters of this computers tuning were worked around emissions, not efficiency. I don't doubt that the system exit's lean burn and dumps fuel to heat the cat to keep it operating. I've heard that the new diesels are doing the same thing and have lower mpg ratings as a result.

Are you sure about this? Haven't studied too much into the D15Z3 operation, but both engines have the wideband. An ecu must hear knock before it can retard timing and honda's knock boards (at least the OBD 1 versions) were the equivalent of silicon excrement. I find it difficult to believe any manufacturer would intentionally set a system up ignition and timing wise to operate at the mercy of the knock sensor which would need to hear detonation in order to maintain efficient fueling. Once detonation does occur, air/fuel readings (via the O2) will go lean and skew the fuel trim. If this were the operating principal, it is often difficult to achieve detonation at low manifold pressures. It would be likely that in the instance of leaner than stoich operation, if continued to be leaned out, flame speed would become increasingly slower until misfire would ultimately set in without a whisper of a knock. Besides that, all detonation isn't audible nor detectable by a piezoelectric device, there are levels of detonation - detectable or not, it still is a hindrance to power and economy.

This is theory, but stranger things have been known to happen in the real world with engineers.

I could be wrong, and i haven't studied them either, but don't these lean burn engines all have LAF (Linear Air Fuel) Sensor systems? They can detect how lean the burn is, and then run at 16.0 AFR? If they ran much leaner then that the EPA would refuse to license it on account of the amount of NOx they would produce.

According to Recardo's studies, peak thermal efficiencies generally occurred at about 15% lean which would put the AFR at roughly 16.9, that is to my knowledge, a typical number and is due solely to the fact that combustion temps are colder. Any leaner and flame speed drops off drastically.

According to Stone, highest flame temps occur just rich of stoichiometry, however, sufficient oxygen must be present for NOx to form so it occurs just lean of stoich.

Low ratios of EGR dilution significantly reduce NOx emissions. The catalyst is the booger, it must receive a burst of rich followed by oxygen; a continuous cycle.

http://i12.photobucket.com/albums/a2.../4gaschart.gif Credits to Toyota Motor Sales

I've been wondering why an (older) EFI system switches between lean and rich fuel mixture instead of keeping very close to 14.7:1 ratio. (the 14.7:1 is said to be best for killing emissions) Is it because the control system is not capable doing it or is it for the catalytic converter that actually needs to have different poison after another poison to work properly? Not just steady mixture all the time?

The original closed loop systems used a O2 sensor that really only detected two states: Lean, and Rich. If the sensor said rich, it would get leaned out. If the sensor said lean, it would richen the mix. The cross over point for these sensors was 14.7:1.

Is this what you meant by switching between lean and rich? These systems were fairly good at holding close to 14.7:1.