Faulty Low Oil Pressure By-Pass Switch?

[StarTech]

This engine is in a manufactured carpet cleaning system. The manufacturer is no longer in business and never was very helpful. I do have a wiring diagram for the unit but I am not sure how accurate it is. I will see if I can post it here. It shows a terminal strip with 4 system shut downs, high system water temp, high waste tank level, high engine temp, low oil pressure. A wire from each of these switches comes in one side and a common wire off the other side of the terminal strip goes to the ECM.

Makes sense as you would want the engine to shutdown during any of these condition. Its a hardwired OR-ing system. Hardwire ORs and ANDs gates are easy to do. Its the XOR, NOT, NAND, NOR and XNOR that are much easier done via electronics than with relays, switches, and wiring alone.

I did find the part # for the oil sentry bypass which is install on this engine. The bypass includes wiring and a relay. A note in the description is " * Usable on any engine where the fuel system valve is controlled by a "normally open" oil pressure switch, typically found on gaseous fuel engines."

You know it easy to check a time delay relay. It either delays the switch over, operates as normal relay, or simply don't switch over at all. Electronics do short out or open. Using a test meter simply turn the ignition on and check the delay relay operation.

Your problem maybe that you simply don't have a long enough delay.

[Fulltilt]

Kohler's reply to my recent e-mail concerning the aforementioned mystery oil pressure :
" Nominal oil pressure for the LH775 is 25-45 psi. The oil pressure switch does not interface with the fuel injection system. The oil pressure switch is normally closed and is used to illuminate a low oil pressure lamp or activate the safety interlock system. There is an oil temperature switch for the EFI system."

[StarTech]

Also, according to the service manual, the oil sentry switch is a simple open-close switch, with no variable resistance. It also doesn't show up in the engine wiring diagram, and, like I said, the only thing showing in the diagram is wiring from pin #25 to a "safety switch" which more than likely means it connects to the machine's harness, so...
He needs to post his machines numbers.

This engine is in a manufactured carpet cleaning system. The manufacturer is no longer in business and never was very helpful. I do have a wiring diagram for the unit but I am not sure how accurate it is. I will see if I can post it here. It shows a terminal strip with 4 system shut downs, high system water temp, high waste tank level, high engine temp, low oil pressure. A wire from each of these switches comes in one side and a common wire off the other side of the terminal strip goes to the ECM.
I did find the part # for the oil sentry bypass which is install on this engine. The bypass includes wiring and a relay. A note in the description is " * Usable on any engine where the fuel system valve is controlled by a "normally open" oil pressure switch, typically found on gaseous fuel engines."

The oil pressure switch does not interface with the fuel injection system. The oil pressure switch is normally closed and is used to illuminate a low oil pressure lamp or activate the safety interlock system. There is an oil temperature switch for the EFI system."

I would need to differ with Kohler to a point then as the oil pressure switch is wired as a safety shutdown for the ECM. In the quoted text is exactly how the oil pressure switch is wired as a safety switch tied to pin 25 hence the reason for the delay relay. The oil pressure switch does interface with the ECM module via the hardwired ORing setup (high system water temp or high waste tank level or high engine temp or low oil pressure) that feeds the pin 25 safety shutdown terminal of the ECM.

You might notice one statement says normally open and the other says normally closed. This depends on how you describe what is normal operating condition.