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Old 09-19-2004, 07:58   #1 (permalink)
Con
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Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

There has been a lot of talk on changing Air Fuel Ratios when the ECU is operating in closed loop. Here is my spin on the subject.

The Problem:
If the ECU does not see 450mV-600mV it will keep on changing the mixture until it gets to 450mV-600mV. If it cant get there it will go into limp home mode.

For example lets say the Heated Exhaust Gas Oxygen (HEGO) sensor voltages are:

1.20 50mV lean
1.10 60mV lean economy
1.05 70mV economy
1.00 450mV stoichiometric (14.7:1)
0.90 750mV power
0.85 800mV rich power
0.80 850mV rich
As you can see the HEGO has a very narrow band of opperation. There is very little voltage difference between economy/lean and power/rich.



So when the ECU is in closed loop this is what we want it to see for us to achieve maximum economy.
1.20 50mV lean
1.10 450mV lean economy
1.05 600mV economy
1.00 750mV stoichiometric (14.7:1)
0.90 750mV power
0.85 800mV rich power
0.80 850mV rich

Here is the difference between the HEGO and ideal.

1.20 0mV lean
1.10 +390mV lean economy
1.05 +530mV economy
1.00 +300mV stoichiometric (14.7:1)
0.90 0mV power
0.85 0mV power
0.80 0mV rich

There is no linear relationship here. A resistor, linear amplifier or constant voltage will not be able to change the HEGO to ideal.

The problem with using a digital microcontroller interceptor and narrow band HEGO is that the voltage differences are so small that a change in temperature will change the tune significantly.

I dont even think an "aftermarket chip" would change the closed loop AFR.
Maybe someone with a Unichip could test this for us?

Solution:
We will use a wideband AFR meter. Most of these units have an analogue output where voltage is proportional to the AFR. Here is an example:


Here is a rough circuit i quickly made up:

50mV is always connected to the ECU.
450mV is switched on at >3.5V equivalent of 15.5:1 (lambda 1.05)
800mV is switched on at >3.75V equivalent of 16:1 (lambda 1.09)
The result will be that at cruise the ECU will try and keep the AFR between lambda 1.05 and 1.09.
The switch is so that it can go back to stock easily. This means you can use the wideband AFR meter on yuor other cars!

Here: http://wbo2.com is a really good wideband AFR meter for only $355 if you DIY.

This is a handy little project that will tell you when the ECU is in closed loop.
Autospeed - Closed Loop Monitor:
http://www.autospeed.com.au/cms/A_17...popularArticle

Reference Threads.
Sensors Information
air fuel ratios???

It will probly be about 1/3 of the price of an EMS 8860 or Unichip
Do you guys think this will work?

ps) Now that you have a wideband AFR meter you can reduce the fuel pressure. This will bring your AFR from 0.75 lambda or worse back to 0.85 lambda. You will get an increase in power and economy when the computer is reading off its stored fuel maps. You will have fully functional closed loop mode too.

pps) do you have to change the timing when running lean?
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Old 09-19-2004, 12:28   #2 (permalink)
Jim Mock You Rock
 
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

Man can we just stick one in?Ive benn looking at it for 3 days and am not sure..
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Old 09-19-2004, 17:09   #3 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

sticking in an adjustable fuel pressure reg will not change the closed loop AFRs.

The way to get around this is to never let the computer go into closed loop mode. turbotrana disconnected his HEGO and got this to work. you are still going to need a wideband AFR meter to tune it. and the wideband is most of the cost...
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Old 09-19-2004, 17:13   #4 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

If you mean just sticking in a wideband HEGO thats not going to work. the wideband HEGO needs a fair bit of electronic control to run it.
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Old 09-19-2004, 17:37   #5 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

follow turbo torana's lead on this.

He has the best understanding of how to do this as far as I ma concerned.

Adjustable fuel regulator and wide band HEGO and then build a fuel pressure map to suit the A/F ratio u want.
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Old 09-25-2004, 19:54   #6 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

The loop monitor mentioned showed a link but the link went to an ad. for a magazine.
What does it do and how is it connected?
Also curious about the changed input to the computer from the HEGO. The information about the HEGO seems to indicate that it is part of a negative feedback loop which maintains the most efficient combustion of the fuel. Non linear amplifiers are not difficult to make ( maybe a couple of transistors and a diode) but the control of the mixture must be programmed into the computer and that could be non linear.
Two sites just visited
http://www.bobblick.com/techref/proj.../o2sensor.html
http://www.mr2.com/TEXT/O2_Sensor.html (self powered oxygen sensor)
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Old 09-25-2004, 21:08   #7 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

Thats a pretty cool idea ,maybe getting the resistor values might be tricky though , perhaps that air-fuel kit listed on jaycar could be used to program the right values.

AFAIK the SMT-6 piggyback can modify O2 sensor output , dunno about the others.
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Old 09-26-2004, 07:18   #8 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

I've had the wide band a/f ratio sensor (cost $300+) in with the standard ECC4. Basically what happens is when it switches to closed loop while cruising it adjusts it really lean and really rich to the point that you can feel the engine dropping off power as it goes into the lean loop (if this makes sense or answers any questions as I did not read the earlier post in any detail), so its no point using it.
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Old 09-26-2004, 18:01   #9 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

The author of one of those links thought that the best way to solve all the problems was to earn more to buy a new car more often.
I will try connecting a digital multimeter to the oxygen sensor. It has an input impedance of 10 meg. Probably just push a pin through the sensor output wire to connect.
There is a problem of the car not wanting to start after standing hot for a certain time. The pump tests good on pressure and resistance and always starts when cold or hot (if the time is not the problem range). Now have fitted a small lamp above the back seat which monitors the voltage to the pump. It was an easy connection using small strips of spring brass pushed into the back of the plug. Also have a monitor for the spark using a 8cm wide strip of al. foil wrapped around the output lead from the coil and connected to a small neon. This gives a very visible glow in the cabin near the hood release. It looks from the circuit that the computer can disable everything.
I need to know the logic behind any changes and this car is a slow learning curve.
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Old 09-27-2004, 18:27   #10 (permalink)
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Re: Changing the Exhaust Gas Oxygen sensor to give better ECONOMY!

I am not sure about my understanding of the fuel control system but had the idea that a small adjustment could be possible to the sensor control. This would have to be guided by just how the engine was using fuel under different driving conditions.
This circuit may not be suitable but will illustrate the idea.
The circuit may not be correct but should have a gain of 1 and have an adjustable output volts level pos. or neg. ?
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