94 OMC Turbojet 115 hp - alarm causes

[pit-q]

What different faults cause the alarm to sound in my Jet Boat with a 115 hp omc turbo jet. I don't have an engine manual.

Also, what effect would a little water in the gas have on performance? Noise, hesitation or what.

pit-q

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

Overheat warning is a continuous horn.
No Oil is continuous short pulses.
Low oil is short pulses every 40 seconds.

Because gasoline floats on water and because the fuel pickup is at the low point on the tank, water in the fuel is serious. You can install a full sized water separating fuel filter near the tank, and you can use dry gas to help mix the water into the fuel temporarily if you want to try to burn through the fuel.

 

[ko49028]

Re: 94 OMC Turbojet 115 hp - alarm causes

I am trying to fix a 96 OMC Turbojet (115hp) that has a solid alarm. According to the previous reply, it is the temp sensor. I'm having trouble locating the sensor. Where would it be? What does it look like? Is there more than one? How hard is it to change? And lastly (for now), is there a way to test/fix the sensor? Any help is appreciated. Thanks.

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

The temp sensors are switches embedded below the water covers on each cylinder head. Each one has a tan wire with a disconnect located a few inches from the cylinder head.

If the switch is faulty, disconnecting the wires near the cylinder head will silence the alarm.

It would be nearly impossible to remove the individual switches for testing without pulling the powerhead out of the boat.

 

[ko49028]

Re: 94 OMC Turbojet 115 hp - alarm causes

Further investigation and information... There only appears to be 2 temp sensors of 4 cylinders on opposite cylinders. Disconnecting them results in the same solid alarm. Further, I have no spark at any cylinder. On maybe 2 occurences, I've moved some wires investigating behind the dash and the beeping has stopped and the engine started but on the very next try the alarm is on again. I've not had the boat on the water yet (only backed into a launch with boat on trailer). All connections seem correct. Even disconnecting the harness at the motor gives the alarm. Is it possible that it is the alarm itself shorting something out or the ignition switch? I'm open to further suggestions. Thanks.

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

Right, total of two cylinder heads and two temp switches. If disconnecting the tan wires results in no change, the tan wire is shorted or the horn is bad.

BTW, the temp switches are one thing OMC got right - they hardly ever fail.

Unless you install temperature gauges, you really must have working temp switches and a working horn.

The horn is supposed to give a short test beep when you first turn the key to run.
After that it should stay silent. If you disconnect the tan wire from the horn and the horn goes quiet, its the wire. If you disconnect the tan wire and the horn keeps going, replace the horn.

Edit: before replacing the horn, make sure that the horn is wired correctly: There should be a plus on the horn case next to one of the spade connectors that should be connected to a purple positive wire off your ignition switch. The other spade connector should be connected to the tan wire. The odd wire that runs from within the potting connects to the small black ground M on the ignition switch.

 

[ko49028]

Re: 94 OMC Turbojet 115 hp - alarm causes

All is wired correctly. Disconnecting tan wire causes alarm to go silent. What else do I have to check regarding the tan wire? Anything regarding the oil? I'm unsure what other items provide a signal to the tan wire.

I truly appreciate all of this knowledge and help.

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

The engine wiring harness was OMC. The console wiring is the boat manufacturer's The tan wires are standard OMC and the tan wire is a common grounding sytem for all of the horn's alarms including the OMS.

See if the main harness has a large red plug at the engine. Do you have a ohmmeter?

 

[ko49028]

Re: 94 OMC Turbojet 115 hp - alarm causes

OMS?

Yes - large red plug at engine.

Yes - I have an ohmmeter.

Next step(s)?

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

The tan wire in the engine side red plug should not have continuity with anything. Put one probe on the connector inside the plug and one on a good ground contact on the engine block. It should show no reading.

The tan wire on the console side red plug should not have continuity with anything but itself either. Put a probe on the tan wire inside the red plug and one to the engine block. Then probe the other points inside the red plug to be sure that the wires have not fused. .

Click the thumbnail:

 

[ko49028]

Re: 94 OMC Turbojet 115 hp - alarm causes

The Console side seems to check out ok.

The Motor side is a little mysterious. With the leads in one configuration (red lead on tan pin), all is well. When the leads are switched, (black lead on tan pin) the Red/Purple Stripe (per your diagram) then shows continuity with every other pin including tan, and engine block.

Am I missing something?

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

No, there is a blocking diode on the harness to keep the OMS (A/K/A VRO) signal from flowing the wrong way and it is functioning exactly as it is supposed to.

You will need to start looking on that side for the cause of that going to ground.

You have eliminated the temp switches, so disconnect the oil tank's black and tan bullet connectors, then the fuel pump's 4 wire amphenol, then look at the wires themselves. Somewhere there is a tan wire grounding out.

 

[SKEETR]

Re: 94 OMC Turbojet 115 hp - alarm causes

After you get your alarm worked out I highly suggest installing an inline water filter. If you don't have one on there already. Because these motors work extra hard to turn that jet you need to ensure relatively clean water to prevent overheating them.

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

Don't connect anything else to the purple and red wire (that's the positive fused circuit); if positive voltage flows to the powerpack or rectifier, they will be damaged. Keep the battery disconnected until you finish troubleshooting.

 

[ko49028]

Re: 94 OMC Turbojet 115 hp - alarm causes

The oil tank was disconnected along with the fuel pump, both resulting in the same alarm. I don't see any wire damage thus far.

On a separate note, the alarm itself still seems suspect because upon moving it and setting it in random positions it will shut off momentarily and then come back on.

Would a bad alarm cause no spark at the plugs, or is it possible it just needs replacing and I still have grounding problem some where?

 

[ezeke]

Re: 94 OMC Turbojet 115 hp - alarm causes

The black and yellow kill wire from the ignition switch and the emergency lanyard ground the powerpack and immediately stop any possibility of spark fire.

In addition, you need a fully charged battery to get the engine moving at 300RPM to get spark.

Check spark on a crossflow with all plugs removed, using a spark tester capable of being set at 7/16 gap.

Use the diagrams at this link by scrolling to the bottom: http://continuouswave.com/whaler/reference/ignitionSwitch.html

The horn has a direct positive connection to the purple wire on the ignition switch. The circuit is completed when the tan wire is grounded somewhere. The test wire coming from the potting on the horn is a momentary ground, so you could disconnect it and see if there is a change.