1999 7.4 MPI. 15 hrs. Alarm goes off when above 1000 RPM. Cold engine it takes 10 minutes, hot, it takes about 5. Beep is every 3 seconds. Even tho this engine is basically new I replaced water pump, thermostat, backflushed all the lines. Outdrive oil is full. Oil pressure is good. Water temp is between 150 and 175 depending on RPM. Doesn't matter if I use hose or put in the water. A couple of things to help. 1- If I shut off engine and immediately turn it back on it takes the few minutes to sound alarm again. 2-It runs perfectly all thru the RPM range,even above 4000. Does not act like it's starved for fuel. Thanks for any ideas. Also, what's the best way to test the sending units and the oil res. unit.

sounds like it would be the oil pressure
maybe you are losing enough at higher rpms
like you mentioned, I would have the senders tested or replaced.

possible fume detector? Just a thought. Check for a fuel leak. Had this problem after a fuel filter/water separator change.

after the alarm sounds, merely open the engine bay & remove then re-attach leads to each alarm sensor. When the alarm goes off (quiet) then you know which sensor is tripping the alarm. The sensor may be bad. All the sensor does is ground the lead to the alarm which is a common wire. All sensors are wired in parallel to this common wire, so any sensor can activate ground on the lead.
Once you know which sensor is causing the alarm, I would replace it as probably defective, as your temp, pressure, drive oil, etc seem adequate. Good luck!!

BlownFormula

Thats how i tested them. Unhooked gear lube bootle and oil pressure sensor created no change.

The temp sensor is the oddball. If i unhook it while beeping, no change. If I unhook it at low RMP when there's no beeping, it sets off the alarm. It shouldn't do this, should it? Does this mean there is a problem with the wiring to this sensor?

Again, THANKS TO ALL for your help.

Wade

no it should not !! All alarms are triggered by a ground. It will only sound if that ground is present. When it is removed, the alarm should go silent. There is no "computer" that registers & holds the alarm. It is ground based only. If the offending sensor is disconnected, the alarm has to go off, unless more than one sensor is tripping it. You can test for this with an ohm meter on the alarm lead. You may have to leave multiple leads disconnected to find the final answer.

If I have all three disconnected, the alarm sounds at all rpm's. At low rpm if I then reconnect the temp sensor only, the alarm stops.

Wade

OK, with the three sensors disconnected, use an ohm meter to find what is causing the alarm. That alarm wire has several splice points in it as part of the Merc harness, somewhere it may be shorted to ground or in a really rare case to battery & feeding back thru the "screamer". I bet on the ground lead tho' . Measure that lead with all sensors disconnected and see if a ground is present. (it will be) then trace all brown wires with a blue tracer.......see Merc wiring diagram. good luck

Is there a fuel pressure sensor????

Thanks blown. That' what i'll do.

No fuel pressure sensor on this one.

Wade

There may be two temp sending units. One for the gauge and one for the alarm. Make sure you have unhooked the right one.

Ron