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Old 03-07-2019, 01:47 AM   #1 (permalink)
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Idle Rich /Lean -inputs to ECU

What is the main input to idle ECU mapping --IAT , O2 sensor ,CTS or a combination of all three.

Reason is I have my hho map enhahncer setup with O2 enhancer .
All is good from above idle , but the idle appears to back to the 14,7 so it is bypassing the changes on the O2 and vacuum .

Thanks in advance

Brad

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Old 03-10-2019, 09:52 AM   #2 (permalink)
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Presumably the air fuel ratio displayed is from the O2 sensor. If you add hydrogen to the intake air, the O2 sensor read "rich" and pull fuel until it sees stoichiometric burn, which it will assume to be 14.7:1. You can add as much hydrogen as you want but you'll always see 14.7:1 as the O2 sensor is trying to get the ratio of oxygen to fuel correct, and the computer is assuming whatever that ratio is, to be 14.7:1.

You will of course be burning less gasoline and more hydrogen. Is hydrogen cheaper than gasoline per BTU in South Africa?
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Old 03-10-2019, 10:25 AM   #3 (permalink)
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Thanks for response.

Currently the ECU has a narrow band O2 sensor -- when I upgraded to free flow front to back with Cowley boxes -straight through_I added the wide band AFR gauge which has been very good for the measurements.
I have a dry cell hydrogen with an Efie at 150 mV set currently for O2 and Map enhancer for adjusting the vacuum that the ECU is seeing .

I set up the Map enhancer and can lean it out, BUT I think the ECU is overriding the mods I have added due the mapping and the IAT input .

Today once it stops raining I am planning to install the IAT parallel resistor network to make the ECU think it is getting a higher temperature and so I am assuming it will lean out across the maps .

My last mod if required is to raise the CTS input then I have pretty much all mods needed .

I did have a Volo_VP15 BUT it seems to not change my ECU or anything due to my protocol - pity as it would be easier but thats how it goes with my old model 2001 Legacy GX.(My protocol is the 1941 and not the recent CAN bus).
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Old 03-10-2019, 10:43 AM   #4 (permalink)
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You shouldn't need to adjust any sensors if your car uses a MAP sensor, that's all myth. The O2 sensor will make sure the amount of air vs fuel is "correct" (stoichiometric), because it looks for any unburnt oxygen in the exhaust and adjusts fuel up or down so that there's zero (but no extra fuel either). Doesn't matter if you're adding nitrous oxide, hydrogen, propane, natural gas or whatever else to the intake or combustion chamber, the O2 sensor will take care of it, and the ECU will add or subtract fuel so that combustion is correct. It should always show up as 14.7:1.
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Old 03-10-2019, 10:56 AM   #5 (permalink)
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OK noted - I seem to have something overriding whatever I set the MAp to , I do not have a Cat converter, so my AFR I should be able to run slightly leaner at 15-16 without any issues.From my understanding ,the stoich for CAT's is set so as not to damage them long term .One should be able to run an engine of this type safely up at around 16-17 AFR . This will allow more gains then additionional hho will assist to further the baseline gains .(Perhaps I am missing the understanding and am not taking into account additional aspects to adding hho )

If the map and O2 was the only inputs controlling the ECU mapping I would think that whatever I set is used but again I find something taking the AFR ratio back to the 14.7 which is defying my understanding of adding the hho and getting any mpg gains.

Friday I ran 5 Amps on dry cell and after filling up the calculation was same before with no mods or hho - 0,79 l per 100 km.(My average has been 0,8 for a few years now , before the dry cell .)
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Old 03-10-2019, 11:24 AM   #6 (permalink)
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You're 100% right about catalysts - running leaner (15-16:1) will damage them if you don't occasionally dump a little fuel in them to purge them. Honda's lean burn engines will occasionally run rich for 10-20 seconds to "purge" the cats and keep them healthy.

So, I assume you're reading your AFR using your standalone wideband gauge?

To my knowledge one way to get a leaner air fuel ratio is to offset the O2 sensor voltage with an interceptor. If you adjust it so that the ECU sees the correct voltage for 14.7:1 when it's actually 16:1, the ECU will hold that air fuel ratio. However the ECU will only do this when it's in "closed loop". Any time it goes into open loop operation it will fall back on its fuel tables and ignore the sensors.

I'd like to give a word of caution about this, however, and suggest that a much better and safer way of going slightly lean is to use aftermarket engine management and a wideband sensor for the ECU. Reason being, exhaust temperature rises and peaks around 15.5-16.0 AFR. It's fine to run these AFRs when the engine is at low RPM and low load, but if you stay lean while accelerating briskly (e.g. trying to pass someone on the highway or getting up to speed to merge) you can burn your exhaust valves. Cars that come from the factory with lean burn do not run lean under heavy loads or at high RPM, and you have no easy way of preventing this with a simple O2 sensor interceptor.

Regarding any HHO gains, the typical answer on this forum which is backed up by a lot of scientific study on the topic is that the amount you should expect under most circumstances is either zero, or negative. Making hydrogen gas is an energy-lossy process - it's low efficiency, so using energy to split water and then recombining oxygen and hydrogen back into water in the combustion chamber will net less overall energy and hurt fuel economy. It shouldn't matter in practice though as realistically, the amount of HHO you can produce in a car is going to be such a tiny percent of intake mixture as to disappear into background noise.

I've read a few studies suggesting that there are a few edge cases where the addition of hydrogen can be beneficial to fuel economy, but it's almost always still negative in terms of cost per mile because of either the cost of buying hydrogen, or the lossy nature of generating it yourself.

Under stoichiometric combustion, modern engines release greater than 99% of energy stored in the fuel, so there are basically no gains to be had there. Most losses occur as heat is lost through cylinder walls and goes out the radiator, through friction in piston rings, bearings, gears moving through viscous oil, etc. making these better places to look for improvement (not to mention tires and aero drag), so things like reducing RPM (taller gearing to reduce piston speed), running thinner oil, higher temperature thermostats to reduce temperature gradient, etc. are better places to look for improvements. HOWEVER, under some extremely lean conditions, in some combustion chambers which are not designed for lean combustion, when you've leaned out sufficiently that gasoline does not burn fully (which ruins fuel economy) and the engine is running rough/poorly, the addition of hydrogen can partially restore some of that lost combustion efficiency. Running lean when your gearing is poor and your engine is not properly loaded can reduce pumping losses and the addition of hydrogen *might* help keep combustion efficient. You're probably better off just not running that lean though if you aren't injecting hydrogen you supply with a tank.

I could not tell you offhand what the efficiency of a 5 amp dry cell is, so the following back of the envelope math is not to be taken too seriously. However, if we can assume a very generous 50% efficiency of the dry cell, you'd get maybe ~30 watts worth of hydrogen from a 5 amp cell. Multiply that by 33% efficient combustion and at highway cruising speed, hydrogen generated will make up in the ballpark of 0.05% of "fuel" in the combustion chamber. I'd wager you'd need in the ballpark of 20-100x this to see any appreciable effects, so it's no wonder your fuel economy is the same. Look into a 200-1000 amp dry cell or tank hydrogen if you'd like to play with it and see if it can help stabilize very lean air fuel mixtures.

My 2 cents.


Last edited by Ecky; 03-10-2019 at 11:42 AM..
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