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Old 07-30-2007, 11:03 AM   #1
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sensor mods

I have been playing around with iat and ect sensors. I know these sensor control the pulse width of the fuel and timing in the computer on the car called the ecm. What I have found out if anybody all ready knows is that all closed loop cars run anywhere between 5 to 15% richer in the fuel charge. They do this so the cats will have something to burn also.... So we all are burning way more than we need to also, if the o2 sensor reads the fuel charge is to rich should it alone be the one that tells the ecm to trim the fuel charge not reburn it again... This is hogwash about everybody thinking I will drive up my no2 is BS. I have modded my iat and sniffed the pipe and all in is good in the enviro club.. So the next mod is the ect to trim the fuel....Anybody have more to say on this topic
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Old 07-30-2007, 11:16 AM   #2
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1) Most (if not all) new cars operate at stoichiomentric air/fuel ratio..... neither lean nor rich. This is so that "3-way" catalysts will have enough HC and CO to reduce the NOx. That's the reason that all new cars have an oxygen sensor, to measure and control the engine at stoichiometric oxygen levels.

2) Fuel economy is better under lean conditions for several reasons: Fuel burns more completely with excess air; amd throttler settings are higher for a given engines torque, reducing the vacuum against whcih the engine has to work. But lean conditions produce more NOx.

3) The exception is ultra-lean burn. Direct injection, ultra lean engines can achieve better fuel economy than ordinary engines for the above two reasons, AND ultra-lean engines do not produce as much NOx because peak combustion temperatures are low.

4) NOx from an engine is mostly NO, which is odorless. Sniffing exhaust will not detect NOx. It's a bad idea to sniff exhaust, BTW.
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Old 07-30-2007, 11:29 AM   #3
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sensor mods

Quote:
Originally Posted by Sludgy View Post
1) Most (if not all) new cars operate at stoichiomentric air/fuel ratio..... neither lean nor rich. This is so that "3-way" catalysts will have enough HC and CO to reduce the NOx. That's the reason that all new cars have an oxygen sensor, to measure and control the engine at stoichiometric oxygen levels.

2) Fuel economy is better under lean conditions for several reasons: Fuel burns more completely with excess air; amd throttler settings are higher for a given engines torque, reducing the vacuum against whcih the engine has to work. But lean conditions produce more NOx.

3) The exception is ultra-lean burn. Direct injection, ultra lean engines can achieve better fuel economy than ordinary engines for the above two reasons, AND ultra-lean engines do not produce as much NOx because peak combustion temperatures are low.

4) NOx from an engine is mostly NO, which is odorless. Sniffing exhaust will not detect NOx. It's a bad idea to sniff exhaust, BTW.
The stoichiomentric air/fuel ratio is good rule of thumb but to get the cats to lite off the extra fuel is in the combustion to do so.. Also, ultra -lean burn cars peak temps have many things mixed in to reduce peak temps also more fuel automatically does this but also timing can helped.And sniffing the exhaust is done by air care machine not by the nose but you can try , I would rather use the proper devices to make my statement.
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Old 07-30-2007, 02:55 PM   #4
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Green Swift:

Try it and see what happens.
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Old 07-31-2007, 12:15 AM   #5
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The car runs extra rich to light off the cat when the engine is first started and when it's not up to operating temp yet. Once it's warmed up extra richness isn't needed.

Cylinder head temps and exhaust gas temps will drop when A/F ratios are above 15.5:1 or thereabouts. The tendency to knock also drops off at leaner A/F ratios.
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Old 07-31-2007, 02:11 PM   #6
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Less is more

A quick search of the web shows ECUs trying to maintain 02 sensors output at 0.4 - 0.5 V. This chart from better-mileage.com shows this voltage range to be richer than a stoichiomentric ratio. So I'll have to agree with green swift that a stock engine is running slightly rich.



I'm also seeing estimates of 5 & 10% savings with an EFIE device from better-milage.com and eagle-research.com (who's trying to sell something and quotes the higher %). This seems to reinforce the slightly-rich ratio theory, also.

An EFIE and a mixture display are on my long-term plans.
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Old 07-31-2007, 07:32 PM   #7
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The brand of o2 sensor can make a difference in mileage also. I have a Innovate wide band o2 for datalogging along with a narrow band for the ecm control. I have personally observed a brand new narrow band Bosch o2 sensor tell the ecm that 14.1 ~ 14.2 AFR was stoich. And no, it was not an E85 blend of fuel either. On the same tank of fuel a narrow band Delco o2 sensor read pretty much right on the money at 14.7. This is probably where Bosch gets away with claiming better performance with their o2 sensors, they trick the ecm into running a little richer. Wish I could give more info on other brands but thought I would share what I have observed.

Brian
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