Oil Injection Alarm at High RPM's

[achilles555]

I have a 1988 Mercury XR4 150. I've got her running great - but there's one last problem I can't get figured out. When I get past about 1/4 throttle, my Oil Injection Alarm starts beep - beep - beep, and won't stop until I slow the boat down to about 1/4 throttle again. It's not a constant beep, so it's not overheating. It's definitely the oil. I've replaced the sending unit, made sure that my reserve tank was full to the top, and checked both oil tanks and caps for cracks or leaks. I've also pulled the oil pump off, and inspected it for problems. Everything looks good. What's got me buffaloed is that it only starts beeping at the higher RPM's. Anyone out there have any suggestions?

FYI - I've pre-mixed the gas and oil 50:1 until I get this thing figured out.

Thanks for the help. AC.

[THEFERMANATOR]

Have you removed the oil pump driveshaft and checked the crank gear? Sounds like your plastic crank gear may be slipping under load. Or your water in fuel could be tripping it.

[achilles555]

Fermanator - thanks for the suggestion. I went through the oil pump, shaft, and bearing last night. Everything looked good. I even replaced the sensor and bearing this morning. No luck. Same beeping. I do have some good news though, I think...

I had one last thing to try that was suggested to me by a fellow Merc owner over at iBoats. He suggested switching the wire that connects to the same post on my switch box as the number 2 cylinder. He suggested removing the wire from the number 2 cylinder, and trying it on another cylinder on the OTHER switch box. That wire regulates voltage being sent to the spark plug (I think).

Anyway, I did as was suggested...and sure enough, the beeping stopped at the higher RPM's. I'm not 100% sure what that means. Maybe a new stator? I need to find out. It's great to know that I'm on the right track, though.

It does still beep a little, but only at about 1/2 throttle. It beeps a couple of times, then stops.

Thanks again for the help. If any of this sounds familiar to you, let me know what your next course of action would be. AC.

[Steve Pope]

You have a faulty swich box.Steve

[pyro]

More likely a faulty oil warning module. They go bad all the time, and this is usually what happens when they do.

When you checked the pump and gear, how did you check the drive gear. It's a large, plastic gear around the middle of the crank. This is the part that goes bad when the oil injection system fails.

Bypass the oil tee in the fuel line and verify oil pump output: Connect a remote tank of pre-mix, purge and prime the fuel system to flush out the straight gas, then run it at WOT with the oil pump output dumping into a catch cup placed in the lower cowling. Take it for a ride to verify oil output.

With as un-reliable as the Merc oil injection system is, especially at high RPM's, and the tendency for its own warning system to fail, your best move would be to remove the system entirely. Tanks, hoses, warning module, just unplug it all, and premix at 50:1. The overheat alarm is triggered by a hard-wired connection separate from the warning module.

No more worries.