I put a new ECM in tonight. We took the boat (1997 Fountain 27 with 502mpi) down to the lake to test it and had no oil pressure and low oil press indicator light was on. When I say low I dont mean zero I mean gauge laying as far left as it can past zero. In the past few weeks i have had a no start senario which prompted the ECM change out and fixed it. I would turn the key on and the gauge was pegged. I changed the oil press sending unit because I did not have continuity between the hex and the plug and thought that may have something to do with the computer not allowing the injectors to fire.(long shot)
The funny thing is now if you have low or no oil press the ECM should go into limp mode right? I just ran down the lake at 5000 RPM with supposedly no oil press and idled in the bay for along time listening to it. (45 min total idle and run time) No ticks or knocks. Plus if the top end of the enigine were dry the knock sensor should limp it to right.

Should save you a lot of money on oil changes.

Realistically, maybe you have the wrong sending unit. They are not all the same. Maybe somebody else can chime in here, nut I know an autometer sender won't work with a gaffrig or livorsi guage etc.

Take the wire that connects to your oil pressure gauge and touch it to ground while ignition is on while someone watches the gauge. If it sweeps acrossed you have a problem with sending unit or connection. If it doesn't move then you have a bad gauge or wiring. I can tell you you DON"T haveactual low oil pressure,your motor would have self destructed before you ever got 45 minutes out of it w/ooil pressure. As far as a "guardian" mode,there is nothing I know of in your mefi box that is going to default to a limp mode with zero oil pressure to protect motor,Smitty

Bad guage or sender. If you had no oil pressure, the engine would be banging and knocking or siezed.

im not sure i ever saw that gage diagnostic procedure published anywhere before.

" if bad oil press gage or sender suspected, run boat as fast as it can go for a long time. if motor blows up then replace gage or send or both"

If the polarity of the sender was backwards the gage would act in reverse. Not just lay limp.

Yes, I believe that I have oil press or I would not have ran it that long. I did just find in the manual that a low oil press detection will cause engine to run in power reduction mode limiting throttle usage and the knock sensor will do the same. That must mean that the wire to the sending unit goes through the ECM so it is probably working and the gauge is bad. I will do some testing to verify.

Thanks for the input guys,

Justin

Check the wiring diagrams in your manual. There should be a seperate low oil pressure switch/sender that the computer reads, it doesn't use the guage's sender.
I would say you either have the wrong sender for the guage or it's not grounding.

This will work, you could also try getting some resistors from Radio Shack. I think it runs from 0-80 ohms and install it from the sender wire to ground. You could also purchace a cheap manual gage just to check the pressure.

the sender is a variable resistance to ground. i have seen some become open under normal operating pressures. as pressure increases resistance decreases. all to ground