I could use a little advice on how to diagnose a problem. Our oil pressure gage reads a little over 60 psi with the engine shut down. Running, it reads the same. The alarm that sounds when you start works and shuts off when the engine starts, so I think we are actually getting oil pressure, despite what the gage says. Is the alarm based on the sensor for the oil pressure, or something else?
The gage is made by Beede, but I can't find any specs on it online. If it works like the teleflex gages, or some new Beede gages, at 240 ohms between the sensor wire and ground, it should read zero psi, and with 33 ohms, it should read 80 psi, but that's a big assumption.
I am thinking I will try three things to figure out if it is a gage problem or a transducer issue.
1: Measure the resistance with the sensor wire off and the engine off, I should get around 240 ohms between the sensor and ground. If I don't, bad wire, bad ground or bad sensor.
2: Check for power to the gage.
3: Fake the gage out by feeding it a 33 ohm resistor and see if I get 80 psi. If not, bad gage.
Does this make sense ? If I do have a bad gage, are the sensors standard enough that it will read right if I replace the gage with a new one from teleflex? Where is the bloody thing at on the engine anyway?
Thanks
Dave
Dave,
It sounds like you are on the right track but I may suggest revising your test procedure.
Check for voltage at the oil pressure gage first with the "ignition system" off to verify that there is no voltage present which is the way it should be. If the gage still reads 60 psi, the way I look at it is the gage is spent as it is only an amp meter reading the current flow through the sensor (variable resistor) to the block (ground). The mechanical linkage internal to the gage must have failed.
The alarm should operate on a separate redundant oil pressure sensor and it should be an normally closed, ON/OFF, make or break sensor, (OPS oil pressure switch) preset to a specific oil pressure threshold. It is closed in the no pressure state to allow the alarm to sound when there is no oil pressure and the "ignition" voltage is applied, and open when the pressure limit is reached shutting off the alarm.
Dale
On Jouney, the oil pressure sensor is on the starboard side of the engine, forward of the injector pump, on a separate manifold block that is supplied oil pressure by a hose from the engine. The low oil press switch is indeed separate.
Since a lot of W40 engines only have instrument power when there is fuel pressure, supply a separate 12V source to the DC in side of your gauge and check to make sure it falls to zero when engine off.
Supply a ground to the gauge on the sensor side. It should provide full deflection o the meter.