Went out to a 550bhp/shp ship genset with management problems last week.
MIL light came on on control panel.
FCR system and 5 fault codes stored.
Erased codes and ran up the plant.
No FC reappeared so allowed engine to run for 6 hours, nothing reappeared FC wise so left the ship.
Next day MIL light came on again.
Went back to the job.
FCR system, nothing stored.
Started oscilloscoping system, all sensors and actuators and associating wiring etc and feedback situations, no faults found.
Thinking in great depth about the problem I noted that this exhaust system was fitted with a Catylistic Converter System with both an upstream and downstream O2 ( Lamda sensor ) whose downstream sensor was on top limits but not enough to trigger the necessary FC. Incidentally this is a four wire installation.
Different from a two or three one.
Scoping the sensor and observing the scope pattern against our library stored ideal readings for this engine model no etc I noticed pattern display differences on the voltage side throught the temp. ranges.
Removing the sensor with difficulty ( a lot of them grow/ weld themselves in there, don't rip the insert out ) and measuring the correct resistance it revealed it was well within limits again throught the temp. ranges.
So we know that the only item near to the manufactures listed limits on the engine is the downstream O2 sensor which clearly when scoped displays an " up on the mark " situation when running under load but when removed from the engine and tested for different temperatures for different resistances appears to be within limits.
What you going to do?
How are you going to handle this re the owners?
If you replace the O2 sensor and it doesn't cure the problem this could be your Xmas present to the owners as if you don't handle this situation correctly it's possibly down to you with accusations/thoughts of incorrect diagnosis flying around.
Just to add to the problem remember that this is an intermittent fault and that by disturbing something else you can put off the reoccurance of this defect and it might run on for several days before the MIL light reappears.
In other words we do not want a ( as we call it ) " since you situation " to occur.
So the fault would appear to lie in the downstream O2 sensor but when removed a series of static bench tests says it's ok.
So is it down to the sensor or what? Would you renew the sensor or not?
What you gonna tell the owners?
How are you going to handle it?
What you gonna do?
Remembering The Good Old days, when Chiefs stood watches and all Torque settings were F.T.