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My bike (FZ1) has two atmospheric air pressure sensors - one under the seat and one in the inlet manifold. At idle they're supposed to read the same which is ~99 kPa where I live. The sensor in the inlet manifold reads 102 kPa which creates a lumpy idle and an engine warning light. Off idle the engine runs fine but the light stays on.
The sensor is about as big as a 4x2 Lego brick and costs £175. The nominal output is 3.594-3.684 V at 101.32 kPa/25 degrees C
Does anyone know how these things work and if they can be repaired?
Likely to be a bit of silicon with a resistor deposited on one side. Unless it's the connector not really repairable.
Hmm it seems to work but reads low. I wondered if the sensors are used in anything else instead of paying Yamaha prices 😐
Might be something you could get from a breakers?
Alternatively, can you swap them round to put the good one in the inlet where it's needed, and minic the atmospheric one with a linear voltage regulator? Dunno if this would throw in problems when you went up a mountain though as the ECU map wouldn't be able to correlate the throttle opening and RPM with the expected manifold pressure.
It's probably a standard component you could get from RS that's failed, but in a bit of yamaha plastic to make it fit. So you would have to get it apart to see.
Might be something you could get from a breakers?
Thank you but the few I've contacted that have actually got one only want to sell me the complete harness
Alternatively, can you swap them round to put the good one in the inlet where it’s needed
I understand that The ECU tests them at idle to check that they're both reading the same (emissions maybe?) I'm guessing when the engine is off-idle the manifold pressure reduces and the ECU ignores the sensor under the seat, which is why the engine seems to run fine (maybe a little rich if it thinks it's slightly below sea level)
It’s probably a standard component you could get from RS that’s failed, but in a bit of yamaha plastic to make it fit
It is indeed an encapsulated plastic brick with lug and a 3-pin connector. I just wondered what's inside - electronic or electro-mechanical. Hmm
which is ~99 kPa where I live
Sorry if I've missed something but why do you say "where I live". You know that atmospheric pressure changes quite a bit even, "where you live"? What reliable source are you using to suggest that the motorbike sensor is unreliable (and which one is "wrong")?
What reliable source are you using to suggest that the motorbike sensor is unreliable (and which one is “wrong”)?
Thanks - the manual says both sensors should read ~100 kPa at sea level, ~90 kPa at 1000m, ~80 kPa at 2000m etc. Last time I checked, one was reading 99 kPa which kindof makes sense (on the day) at home 80 m above sea level whereas the other one was reading 102 kPa which is below sea level.
The difference between 99 and 102 doesn't seem likely to be the cause of your problem.
I'd worry about the relative difference rather than the absolute values. Air pressure varies enormously at almost any altitude.
How have you come to the conclusion that the Sensor is at fault?
Plenty of stuff can make the idle lumpy and put a Warning light on.
Tried wiggling the connector?
I know nothing about motorbikes, but a little about cat engines, and have spent a lot of time on them wiggling connectors on misreading sensors.
Does ebay not have a used one you can pick up for less than OEM?
But if you can swap them and check it'll tell you if it's a duff sensor or something else, if the readings are the same as before the sensor isn't the problem, if the high reading moves with the sensor then that is the likely culprit.
Switching them also has the effect (as said above by paladin) of breaking and remaking the connections, which gives you a chance to check for corroded contacts on the sensor loom, which could be creating resistance and giving a false reading - I'd imagine the air intake sensor is more susceptible to water/road dirt ingress than the one under the seat.
The difference between 99 and 102 doesn’t seem likely to be the cause of your problem
How have you come to the conclusion that the Sensor is at fault?
According to the service manual and the rather wonderful built-in diagnostics...
ECU diagnostics fault code 20: Intake air pressure sensor or atmospheric air pressure sensor: the atmospheric pressure sensor output and intake air pressure sensor output differ greatly
Anyway it could be a faulty connection but I just wondered what was inside the sensor - whether it would respond to heating/freezing/hammering before I shell out £175 on a new one.
Does ebay not have a used one you can pick up for less than OEM?
There are some but still expensive and not from vendors I'd trust tbh.
Thanks everyone
They will read the same with ignition on engine NOT running. When engine is running manifold pressure will read much lower as air is pumped out of the inlet manifold with the throttle restricting the flow of air into the manifold. The PCM will usually check the two sensors against each other on ignition on before the engine starts. The sensors usually have a 5v supply, measure this is the same. The sensor sends back a proportionally lower voltage back to the PCM. At ign on engine not running measure return voltages, this should be same for both. Suspect there is a wiring / connector issue giving incorrect voltage somewhere.