Hi all
I am new to BM’s, mine’s an 1150gs and I've not really started tinkering with it yet, but I also have an old Porsche which I do tinker with and I have a reasonably good understanding of motor electronics/ ignition fuelling etc.
And having read through this post there seems to be some confusion on how these systems work
So for those that are not sure how it works these are the basics
All electronic/ fuel injected engines have a “chip” that controls the fuel input into the cylinder, the ignition spark and the advance or retarding of the ignition timing as well as monitoring environmental things such as temperature and altitude and also crank position etc
These chips can/will have multiple maps on them, for different countries emission laws or for different bike configurations etc and as said in a previous message, these will be generic maps and for the UK will probably be set up to meet our emission requirements and not for maximum power/output.
The lambda sensor is a feedback system to the “chip” that monitors the input to balance the fuel mixture, leaning the mixture when the sensor reads rich and richening the mixture when the sensor reads lean. This only comes into play once the engine/sensor has warmed up
Lambda sensors produce a voltage signal that recognises the amount of unburned oxygen in the exhaust. An oxygen sensor is essentially a battery that generates its own voltage. When hot (at least 250 degrees c.), the zirconium dioxide element in the sensor's tip produces a voltage that varies according to the amount of oxygen in the exhaust compared to the ambient oxygen level in the outside air. The greater the difference, the higher the sensor's output voltage.
Sensor output ranges from 0.2 Volts (lean) to 0.8 Volts (rich). A perfectly balanced or "stoichiometric" fuel mixture of 14.7 parts of air to 1 part of fuel gives an average reading of around 0.45 Volts.
The lambda sensor's output voltage doesn't remain constant, however. It flip-flops back and forth from rich to lean. Every time the voltage reverses itself and goes from high to low or vice versa, it's called a "cross count." A good O2 sensor on an injection system should fluctuate from rich to lean about 1 per second. If the number of cross counts is lower than this, it tells you the O2 sensor is getting sluggish and needs to be replaced.
Most lambda sensors will cycle from rich to lean in about 50 to 100 milliseconds, and from lean to rich in 75 to 150 milliseconds. This is referred to as the "transition" time. If the O2 sensor is taking significantly longer to reverse readings, this too is an indication that it is getting sluggish and may need to be replaced.
Observing the sensor's waveform on a scope is a good way to see whether or not it is slowing down with age. If the sensor becomes sluggish, it can create hesitation problems during sudden acceleration.
A lambda sensor's normal life span is 30,000 to 50,000 miles. But the sensor may fail prematurely if it becomes clogged with carbon, or is contaminated by lead from leaded petrol or silicone from an antifreeze leak or from silicone sealer.
As the sensor ages, it becomes sluggish. Eventually it produces an unchanging signal or no signal at all. When this happens the engine may experience drivability problems caused by an overly rich fuel condition. Poor fuel economy, elevated CO and HC emissions, poor idle, and/or hesitation during acceleration are typical complaints.
If the lambda sensor's output is sluggish and does not change (low cross counts & long transition times), the engine computer will not be able to maintain a properly balanced fuel mixture. The engine may run too rich or too lean, depending on the operating conditions. This, in turn, may cause drivability problems such as misfiring, surging, poor idle, and high emissions.
Sometimes an apparent lambda sensor problem is not really a faulty sensor. An air leak in the intake or exhaust manifold or even a fouled spark plug, for example, will cause the lambda sensor to give a false lean indication. The sensor reacts only to the presence or absence of oxygen in the exhaust. It has no way of knowing where the extra oxygen came from. So keep that in mind when diagnosing oxygen sensor problems.
The lambda sensor is also grounded through the exhaust manifold. If rust and corrosion of the manifold gaskets and bolts is creating resistance, it may affect the sensor's output. To rule out a bad ground, use a digital volt meter to check for a voltage drop between the sensor shell and the engine block. More than 0.1v can cause a problem.
If the lambda sensor is removed altogether the chip can (not sure if this is the case with BMW’s) revert to a default/base map which will usually run a slightly richer map than normal, this would be to make sure the engine does not run lean, as running a lean engine will cause detonation or pinking, this is really bad as it can burn holes in pistons in a short time if left like that. However an overly rich running engine is also bad as the excess fuel can “wash” the cylinder of lubrication causing premature wear.
The fitting of the Y pipe in place of the cat would free up power but if the lambda sensor is not replaced, could also cause premature cylinder wear due to a “rich” running conditions
Or a replacement chip could be made to suite the exact specification of the bike, this would then do away with the need for a lambda sensor altogether, the bike would then run only on the map within the chip.
The “Steptoe” plug short could be overriding the lambda sensor (I don’t know if this is the case as I’m not familiar yet with the BM’s) and running the rich map which could give better/ smoother power, as the system is set up for emissions not power.
If someone has a chip reader you can find out how the maps are set up and then would have a better understanding of what the changes are doing.
So some of the “surging” and poor running issues that these bikes seem to suffer with? Could be related to air leaks or poor functioning of the sensor
Sorry for the long post but….
Hope this is helpful!!
phill
