Viper Scot
Viper Owner
Fairly basic question - how is the closed-loop map managed on a 1996 RT/10. I know that later cars have four narrow-band lambdas but how about the 'Gen 1.5'? Thanks in advance.
Standard closed-loop map on 1996 RT/10
- Thread starter Viper Scot
- Start date
kblake905
Viper Owner
Fairly basic questions - what is a closed loop map? What are narrow-band lambdas? What is a Gen 1.5?
AAKVIPER
Enthusiast
Some help on definitions..
Open Loop
Open loop simply means there is no feedback of the result to the ECU. In our case, it means there is no sensing or measuring of the exhaust gas to see how the car is running. The fuel injected is determined by the RPM and throttle position, derived from fuel injector pulse width numbers stored in the fuel maps, and is trimmed for environmental conditions due to air temperature, air pressure and engine temperature.
Closed Loop
Closed loop means there is feedback of the result to the ECU. In our case, it means there is sensing or measuring of the exhaust gas to see how the car is running. This sensing is done by a probe (a galvanic cell) which generates a voltage based on the gas around it. These probes are referred to as Oxygen sensors, Lambda sensors, O2 sensors, Exhaust Gas sensors and probably a few other names as well. I’ll call it a Lambda sensor. Why Lambda you ask?
Lambda
Lambda is a term used to describe the composition of the exhaust gas of combustion. Also called the Excess Air Factor, it is a ratio of the difference between the actual air/fuel ratio and the chemically correct air/fuel ratio. The chemically correct air/fuel ratio is also known as the stoichiometric air/fuel ratio, and is given by the chemical equation for combustion of a fuel in air. If combustion takes place at the chemically correct stoichiometric ratio, the air/fuel ratio for petrol is 14.7:1 and the Lambda number is 1.0. The 14.7:1 bit means that for chemically correct combustion you need 14.7 times as much air (by weight) as you do fuel (again, by weight). By volume it’s around 9,500 litres of air per litre of petrol.
If there is excess fuel (rich) then the Lambda number is less than 1.0. If there is excess oxygen (lean) then the Lambda number is greater than 1.0. So the Lambda number is the actual air/fuel ratio divided by the chemically correct air/fuel ratio.
You’ll notice I’ve avoided using the terms ‘ideal’ or ‘optimum’ or something like that. This is because 14.7:1 is not ideal, etc. It’s just a number defining a chemically correct process in an ideal situation. In reality, the composition of the petrol is not just one hydrocarbon, it’s a combination of quite a few and the chemically correct ratio varies with that. Plus, air is mostly nitrogen, and this nitrogen comes along for the ride and gets mixed up in the products. And combustion is very rarely ideal anyway.
The products of the ideal combustion are CO2 (carbon dioxide) and H2O (water). In reality, the products are CO2, H2O, CO (carbon monoxide), HC (hydrocarbons, unburnt fuel), O2 (oxygen, unused) and NOx (Oxides of Nitrogen). Lots of nasty stuff, which we’ll talk more about later.
Lambda and air/fuel ratio numbers are the same thing expressed differently – for petrol, Lambda 0.9 = 14.7 x 0.9 = 13.2.
Now, back to the Lambda sensor itself. These sensors come in two main types – Narrow Band and Wide Band.
Narrow Band
A Narrow Band Lambda Sensor generates a high voltage if it is in an atmosphere lacking oxygen. If the atmosphere has excess oxygen, a low voltage is generated. In use, a rich mixture gives a voltage of 0.8 – 1.0 volts. A lean mixture gives a voltage of 0.2 – 0.0 volts. The graph below taken from the Tech Edge web site shows the output more clearly. As you can see, there is very little variation on either side of rich or lean, but as it goes from rich to lean the voltage output changes from 0.8 volts to 0.2 volts almost instantly. Note the Lambda range at the bottom of the graph is 0.98 to 1.02 – the transition is very quick.
This means, in practical terms, that the Narrow Band Lambda Sensor is a yes/no type indicator. Yes the exhaust gas shows a rich mixture/no it doesn’t. Simple as that. It has no real use as an indication of mixture apart from rich or lean.
Narrow Band sensors have been around for some time and come in two types - heated and non heated. They can also have one to four wires. Initially, they were one wire – the output voltage, using the vehicle components as the ground path. Then they went to two wires for the signal with a dedicated ground wire, which gave more consistency and less noise to the output. When the first heated probes appeared they were made as 3 wire, being one signal, one heater, one ground, or 4 wire – one signal, signal earth, heater, and heater earth. These days 4 wire sensors are pretty much the standard.
The heater is to warm the sensor up. The sensors don’t work very well until they are hot, and with the emissions laws increasingly reducing the time after start up that a vehicle must start complying, the heater is needed to get the sensor working quickly.
Wide Band
The Wide Band Lambda Sensor differs from the Narrow Band Lambda Sensor quite markedly in its construction and operation. It works by using a supplied voltage to create a chemical reaction that then creates a current based on the mixture of the gas. I don’t understand any more than that, but then I don’t need to. The output of these sensors is non linear, but varies over a very wide range of lambda numbers, from very rich to very lean. As such, they are very useful for tuning. The graph below taken from the Tech Edge web site shows a wide band sensor output. The Lambda number is across the bottom, output in mA, not Volts, up the LH side.
The Wide Band Lambda Sensor comes in two types that I know of. Firstly the older style ‘Bosch Motorsport’ (BMS) sensor with four wires that Duane Mitchell has used for years with his Gold Motec and the Corsetec Lambda meters. Secondly the later ‘Universal Exhaust Gas Oxygen’ (UEGO) sensor with 5 wires that is now coming into wide use with the cheaper Lambda meter/data logger boxes like the LM-1, Dynojet Wideband and local Tech Edge to name a few. These UEGO sensors are also being fitted OEM to many cars in place of the narrow band sensors. How much use is made of their potential I don’t know.
Like the Narrow Band sensors the Wide Band sensors are also heated.
Why Closed Loop?
The main reason for running engines closed loop is for the efficient operation of 3 way Catalytic Convertors. The main reason for running Catalytic Convertors is to chemically change the constituents of the exhaust gas from nasty to not so nasty (because it’s never going to be nice). Catalytic Convertors are very natty pieces of gear, and are responsible for allowing performance to return to vehicles in this age of vehicle emissions control.
Originally, Catalytic Convertors appeared as ‘2 way’, meaning they cleaned up two gases only, CO and HC. While this was good, it left NOx (the various Oxides of Nitrogen) untouched. NOx combined with HC makes up smog, and on their own are responsible for acid rain. The problem with this is that NOx is formed when combustion goes over a certain temperature, so to reduce NOx the temperature of combustion needed to be reduced. But temperature means pressure and lowering the pressure of combustion is fundamentally opposite to good power and efficiency. This is why, in the 70’s and early ‘80s, car engines had lower compression ratios, wacky cams with longer overlap to give natural EGR (exhaust gas recirculation) and generally crappy performance.
When the ‘3 way’ Catalytic Convertor came along and dealt with NOx everyone was well happy again, as this meant combustion temperature and pressure could once again go up. This is why late ‘80s car engines (especially large ones) tend to go a hell of a lot better than those from the early ‘80s. In real terms, 3 way Catalytic Convertors are probably the most important internal combustion engine development alongside digital electronic engine management, especially in terms of emissions control. They can remove around 98% of all harmful exhaust constituents (although they turn any carbon based gas in to CO2) and are the technology that gives rise to things like the SAAB ad campaign of the ‘90s where they claimed that, in a London traffic jam, the gas coming out of their engines was cleaner than the air going into them. In Mother Nature’s battle against the insidious, cancerous virus called the Human Race the 3 way Catalytic Convertor is one for her.
But, for a 3 way Catalytic Convertor to work well, it needs to reach a certain operating temperature. The richer mixtures of warm up help here. Then, once it is hot, it likes the exhaust gas composition to cycle from excess oxygen to lack of oxygen. Just a little variation either side of stoichiometric. Luckily, the output of a Narrow Band Lambda sensor is just what is needed.
The Lambda sensor senses the rich or lean state of the exhaust gas and tells the ECU either rich or lean. The ECU reacts to make the mixture the opposite of what it is. If the mixture is lean, the ECU extends the injector pulse widths to make it rich. It does this in a series of steps, as it has no idea how lean the mixture is. Then, once the mixture has gone rich the ECU shortens the injector pulse widths to make it lean again. This cycle is repeated every second or so, and is by definition a control system using feedback from its output to modify the input. And this is what we call Closed Loop.
I hope this helps..
Arthur
Open Loop
Open loop simply means there is no feedback of the result to the ECU. In our case, it means there is no sensing or measuring of the exhaust gas to see how the car is running. The fuel injected is determined by the RPM and throttle position, derived from fuel injector pulse width numbers stored in the fuel maps, and is trimmed for environmental conditions due to air temperature, air pressure and engine temperature.
Closed Loop
Closed loop means there is feedback of the result to the ECU. In our case, it means there is sensing or measuring of the exhaust gas to see how the car is running. This sensing is done by a probe (a galvanic cell) which generates a voltage based on the gas around it. These probes are referred to as Oxygen sensors, Lambda sensors, O2 sensors, Exhaust Gas sensors and probably a few other names as well. I’ll call it a Lambda sensor. Why Lambda you ask?
Lambda
Lambda is a term used to describe the composition of the exhaust gas of combustion. Also called the Excess Air Factor, it is a ratio of the difference between the actual air/fuel ratio and the chemically correct air/fuel ratio. The chemically correct air/fuel ratio is also known as the stoichiometric air/fuel ratio, and is given by the chemical equation for combustion of a fuel in air. If combustion takes place at the chemically correct stoichiometric ratio, the air/fuel ratio for petrol is 14.7:1 and the Lambda number is 1.0. The 14.7:1 bit means that for chemically correct combustion you need 14.7 times as much air (by weight) as you do fuel (again, by weight). By volume it’s around 9,500 litres of air per litre of petrol.
If there is excess fuel (rich) then the Lambda number is less than 1.0. If there is excess oxygen (lean) then the Lambda number is greater than 1.0. So the Lambda number is the actual air/fuel ratio divided by the chemically correct air/fuel ratio.
You’ll notice I’ve avoided using the terms ‘ideal’ or ‘optimum’ or something like that. This is because 14.7:1 is not ideal, etc. It’s just a number defining a chemically correct process in an ideal situation. In reality, the composition of the petrol is not just one hydrocarbon, it’s a combination of quite a few and the chemically correct ratio varies with that. Plus, air is mostly nitrogen, and this nitrogen comes along for the ride and gets mixed up in the products. And combustion is very rarely ideal anyway.
The products of the ideal combustion are CO2 (carbon dioxide) and H2O (water). In reality, the products are CO2, H2O, CO (carbon monoxide), HC (hydrocarbons, unburnt fuel), O2 (oxygen, unused) and NOx (Oxides of Nitrogen). Lots of nasty stuff, which we’ll talk more about later.
Lambda and air/fuel ratio numbers are the same thing expressed differently – for petrol, Lambda 0.9 = 14.7 x 0.9 = 13.2.
Now, back to the Lambda sensor itself. These sensors come in two main types – Narrow Band and Wide Band.
Narrow Band
A Narrow Band Lambda Sensor generates a high voltage if it is in an atmosphere lacking oxygen. If the atmosphere has excess oxygen, a low voltage is generated. In use, a rich mixture gives a voltage of 0.8 – 1.0 volts. A lean mixture gives a voltage of 0.2 – 0.0 volts. The graph below taken from the Tech Edge web site shows the output more clearly. As you can see, there is very little variation on either side of rich or lean, but as it goes from rich to lean the voltage output changes from 0.8 volts to 0.2 volts almost instantly. Note the Lambda range at the bottom of the graph is 0.98 to 1.02 – the transition is very quick.
This means, in practical terms, that the Narrow Band Lambda Sensor is a yes/no type indicator. Yes the exhaust gas shows a rich mixture/no it doesn’t. Simple as that. It has no real use as an indication of mixture apart from rich or lean.
Narrow Band sensors have been around for some time and come in two types - heated and non heated. They can also have one to four wires. Initially, they were one wire – the output voltage, using the vehicle components as the ground path. Then they went to two wires for the signal with a dedicated ground wire, which gave more consistency and less noise to the output. When the first heated probes appeared they were made as 3 wire, being one signal, one heater, one ground, or 4 wire – one signal, signal earth, heater, and heater earth. These days 4 wire sensors are pretty much the standard.
The heater is to warm the sensor up. The sensors don’t work very well until they are hot, and with the emissions laws increasingly reducing the time after start up that a vehicle must start complying, the heater is needed to get the sensor working quickly.
Wide Band
The Wide Band Lambda Sensor differs from the Narrow Band Lambda Sensor quite markedly in its construction and operation. It works by using a supplied voltage to create a chemical reaction that then creates a current based on the mixture of the gas. I don’t understand any more than that, but then I don’t need to. The output of these sensors is non linear, but varies over a very wide range of lambda numbers, from very rich to very lean. As such, they are very useful for tuning. The graph below taken from the Tech Edge web site shows a wide band sensor output. The Lambda number is across the bottom, output in mA, not Volts, up the LH side.
The Wide Band Lambda Sensor comes in two types that I know of. Firstly the older style ‘Bosch Motorsport’ (BMS) sensor with four wires that Duane Mitchell has used for years with his Gold Motec and the Corsetec Lambda meters. Secondly the later ‘Universal Exhaust Gas Oxygen’ (UEGO) sensor with 5 wires that is now coming into wide use with the cheaper Lambda meter/data logger boxes like the LM-1, Dynojet Wideband and local Tech Edge to name a few. These UEGO sensors are also being fitted OEM to many cars in place of the narrow band sensors. How much use is made of their potential I don’t know.
Like the Narrow Band sensors the Wide Band sensors are also heated.
Why Closed Loop?
The main reason for running engines closed loop is for the efficient operation of 3 way Catalytic Convertors. The main reason for running Catalytic Convertors is to chemically change the constituents of the exhaust gas from nasty to not so nasty (because it’s never going to be nice). Catalytic Convertors are very natty pieces of gear, and are responsible for allowing performance to return to vehicles in this age of vehicle emissions control.
Originally, Catalytic Convertors appeared as ‘2 way’, meaning they cleaned up two gases only, CO and HC. While this was good, it left NOx (the various Oxides of Nitrogen) untouched. NOx combined with HC makes up smog, and on their own are responsible for acid rain. The problem with this is that NOx is formed when combustion goes over a certain temperature, so to reduce NOx the temperature of combustion needed to be reduced. But temperature means pressure and lowering the pressure of combustion is fundamentally opposite to good power and efficiency. This is why, in the 70’s and early ‘80s, car engines had lower compression ratios, wacky cams with longer overlap to give natural EGR (exhaust gas recirculation) and generally crappy performance.
When the ‘3 way’ Catalytic Convertor came along and dealt with NOx everyone was well happy again, as this meant combustion temperature and pressure could once again go up. This is why late ‘80s car engines (especially large ones) tend to go a hell of a lot better than those from the early ‘80s. In real terms, 3 way Catalytic Convertors are probably the most important internal combustion engine development alongside digital electronic engine management, especially in terms of emissions control. They can remove around 98% of all harmful exhaust constituents (although they turn any carbon based gas in to CO2) and are the technology that gives rise to things like the SAAB ad campaign of the ‘90s where they claimed that, in a London traffic jam, the gas coming out of their engines was cleaner than the air going into them. In Mother Nature’s battle against the insidious, cancerous virus called the Human Race the 3 way Catalytic Convertor is one for her.
But, for a 3 way Catalytic Convertor to work well, it needs to reach a certain operating temperature. The richer mixtures of warm up help here. Then, once it is hot, it likes the exhaust gas composition to cycle from excess oxygen to lack of oxygen. Just a little variation either side of stoichiometric. Luckily, the output of a Narrow Band Lambda sensor is just what is needed.
The Lambda sensor senses the rich or lean state of the exhaust gas and tells the ECU either rich or lean. The ECU reacts to make the mixture the opposite of what it is. If the mixture is lean, the ECU extends the injector pulse widths to make it rich. It does this in a series of steps, as it has no idea how lean the mixture is. Then, once the mixture has gone rich the ECU shortens the injector pulse widths to make it lean again. This cycle is repeated every second or so, and is by definition a control system using feedback from its output to modify the input. And this is what we call Closed Loop.
I hope this helps..
Arthur
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GuitarSteve
Enthusiast
And a Gen 1.5 is the 1996 Viper RT/10.
Viper Scot
Viper Owner
Re: Some help on definitions..
A great and informed read there thanks!
Now to work out how to tune my car in closed loop!
A great and informed read there thanks!
Now to work out how to tune my car in closed loop!
blackandblue01
Viper Owner
Arthur, thank you so much for this explanation. I have always been in the dark on this topic. Gonna print it off and put it in my service manual.
AAKVIPER
Enthusiast
Anytime..back in the 1990's I was an EMIC dealer for Accel/DFI for the 5.0 Mustang crowd. We had to install and program the Accel/DFI ECU on them. I have training on start up, after start up enrichment, boost mapping, fuel and ignition map tables, etc. We would take a blank DEI ECU and program form a zero starting point. A rear wheel dyno and wide Band Lambda Sensor was a must and still are for any mapping done on any ECU in my opinion.
The material I posted earlier was bits that I collected from the web. But I also have it printed out for my manuals just in case I have a senior moment.
I hope that I could have helped..ArthurIn the pic is my car.. a Vortec 5.0 fox body with a Gen 6 DFI ECU...It is smooth as a kitten now...with 480 hp at real wheel.
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kblake905
Viper Owner
Thankyou very much Arthur, now I know (probably more than I needed).
For me when the thingamajig isn't talking to the watchamacallit I will call the dealer.
That detailed answer was much appreciated though.
Thankyou
