I have an early M20B25 running on motronic 1.3 with a BTB3 manifold (which has a lambda boss), so I could fit a lambda sensor. I know that a lambda sensor measures the amount of oxygen in the exhaust but that's about it.
Could anyone give me a quick idiots guide to what the ecu does with the lambdas signal and the benefits in fitting one?
Cheers,
Lambda Sensor, is it worth fitting one?
Moderator: martauto
It uses it to fine tune the fuelling.
I'm more familiar with later motronic systems but the idea is the same.
The later systems have two "fuel trims" one which is additive and one which is multiplicative.
While your driving, the ECU adjusts the mixture to its optimal point and over time "learns" by recording how much its had to adjust the fuelling from the base map. For instance a 15year old engine with slightly sticky injectors might need 1% less fuel at idle (as they're sticking and more is entering the engine than it should be) but once up the revs might need 3% more fuel becasue the old injectors arent flowing as they should be.
This would end up as something like a -1% additive and +3% multiplicative fuel trim.
The additive is a fixed quantity thats added irrespective of injection quantity, and multiplicative is as the name suggests a multiplier on the injection quantity.
The advantages are many.
By keeping the engine at stoich on cruise and light throttle you maximise fuel economy. Without a lambda measuring things you kinda need to err on the side of rich running. Secondly when you go full throttle, the lambda is typically ignored (engines always run rich at full throttle which a standard lambda cant measure), but the long term trims are still applied. So if the lambda has caused your long term multi trim to end up at 5% because your injectors are old, then you'll get 5% more fuel at full throttle as well.
Basically, better fuelling all round, meaning better idle, accelleration, drivability etc.
I'm more familiar with later motronic systems but the idea is the same.
The later systems have two "fuel trims" one which is additive and one which is multiplicative.
While your driving, the ECU adjusts the mixture to its optimal point and over time "learns" by recording how much its had to adjust the fuelling from the base map. For instance a 15year old engine with slightly sticky injectors might need 1% less fuel at idle (as they're sticking and more is entering the engine than it should be) but once up the revs might need 3% more fuel becasue the old injectors arent flowing as they should be.
This would end up as something like a -1% additive and +3% multiplicative fuel trim.
The additive is a fixed quantity thats added irrespective of injection quantity, and multiplicative is as the name suggests a multiplier on the injection quantity.
The advantages are many.
By keeping the engine at stoich on cruise and light throttle you maximise fuel economy. Without a lambda measuring things you kinda need to err on the side of rich running. Secondly when you go full throttle, the lambda is typically ignored (engines always run rich at full throttle which a standard lambda cant measure), but the long term trims are still applied. So if the lambda has caused your long term multi trim to end up at 5% because your injectors are old, then you'll get 5% more fuel at full throttle as well.
Basically, better fuelling all round, meaning better idle, accelleration, drivability etc.