1994 Johnson 120 v4 "no oil" warning horn has me stumped

[Bannister 6905]

I recently purchased a bass boat with an extremely low-hour 1994 Johnson 120 outboard.

I have an issue with the "no oil" warning horn sounding - whether on the muffs or on the lake. after 3 or so minutes of running, the horn sounds. When running at speed, it occasionally goes away, but it always starts again after a short time. The motor continues to run fine, even when the horn sounds.

Troubleshooting done so far:

* Repaired all leaking fuel and oil lines (there were several). Confirmed fuel manifold is not cracked.
* Drained all 4 carbs and refilled by pumping the bulb.
* Complete decarb with Seafoam
* New plugs (recommended Champions) after decarb
* Removed oil pick up and checked tank for water, dirty screen, etc (all OK)
* Primer bulb at oil tank is good
* tested VRO pump at idle, using procedure found at http://www.boatpartstore.com/vro.asp VRO was pumping oil at the specified rate at idle.
* Went to 50:1 premix in fuel tank, JIC (at first sign of trouble)
* Confirmed that voltage to battery from motor when running is at spec.
* All battery connections are clean and tight. Battery is good.
* New water pump impeller - PSI at speed is 24psi with a good stream - no overheating.
* Pumping the VRO tank bulb does not make the horn stop (bulb is hard)

The only anomaly I've noticed is that the tach reads fast by about 30% at idle. It is not fluctuating - just reads fast. I also have a minor connection issue with the voltmeter - it sometimes pegs to the left (no voltage), but returns with a tap to the face...I will address soon.

I am out of ideas at this point - I want to retain the VRO system, but this horn issue is making that less and less likely...any help with this issue will be greatly appreciated.

The motor starts and runs perfectly, with the exception of that darn horn.

 

[flyingscott]

which warning are you getting 1 beep per second no oil flow once every 20-30 seconds low oil solid beep is an overheat alarm

 

[Bannister 6905]

It is the "no oil" warning - beeps repeatedly - the higher the RPM, the faster the beeps are.

 

[batman99]

If you "disconnected" VRO wiring, unplugged oil tank wires, plugged Oil lines and manually do 50:1 premix (as showing in https://www.youtube.com/watch?v=7_nAl3qthbI ), then its a different alarm. If disconnect (as per U-Tube clip) and works great, why not leave at pre-mix? re: If it's getting gas, then you know its getting proper amount of oil as well...

 

[flyingscott]

I would find why your tach and voltage meter are not working correctly if you have an electrical issue could be causing your alarm. If not the sensor in the pump is bad and you cannot repair it has to be replaced But I would start with your electrical issues make sure no bare wires. Also did you disconnect the oil line from the pump when you fixed all the hoses

 

[Bannister 6905]

Thanks for the feedback.
Yes, I disconnected the oil feed line from the pump, as it was weeping.
I purged that hose by pumping the bulb 5 times and reattached the hose, once I topped off the feed hose, to eliminate any air in the line. After repairing all the leaking lines, the alarm was the same.
I plan to check the connections on the back of the voltmeter and tach tomorrow and see it that has any effect.

 

[Bannister 6905]

These motors were designed to operate best with the VRO enabled. I don't want to go to premix for several reasons, not the least of which is that my consumption of oil is much greater with premix, and the carbonization issue. These pumps rarely fail - even though they are often blamed for another component's failure.

 

[flyingscott]

Okay do this this is the recommended procedure for reattaching the oil line after you take it off. First you take the hose off the pump and pump it until you get something like 12 oz out of the hose. After that do not reconnect the oil line but start the motor and run it to 1500 rpm until the alarm goes off then shut it off squeeze primer bulb until a little bit of oil comes out now connect it to the pump and do not squeeze the primer bulb when you reconnect the hose and clamp it down . Start the engine run at 1500 rpm until the oil alarm stops. Make sure you have water hooked up and a 50/1 gas mix running while you do this. this is pretty much word for word from my instructions I just replaced my vro pump good luck

 

[Fed]

My OMC guru told me that the VRO compares the crankcase pulses to the tacho pulses and if they don't match up then the alarm will start sounding, or something like that anyway. Maybe the VRO counts the pulses of each?
I think there's a member here (Werner?) who knows all about this stuff so I hope he chimes in.
Back to the problem, I'm betting the tacho grey wire is receiving too many pulses due to a failing diode, either way I bet if you fix the tacho it will also fix the alarm. Interesting thread, I wish I paid moroe attention when the system was first explained to me.

 

[Bannister 6905]

Thanks for all the feedback.
I'm working through the repair manual on the issue, but some special tools are required to test some of the electronic components.
Regarding that diode, exactly where is it located? Is it a part of the rectifier / regulator assembly, or is it a part of the tach?

 

[Fed]

The diodes are in the rectifier/regulator and you need some special gear to test the complete unit.
(Large ammeter, voltmeter, variable load resistor and a test wheel or do it on the water without the test wheel)
With the right gear it would take well under an hour to test so it may be better to get it tested at an authorized OMC dealer.
(This info is from a 1988 90hp manual but I'm sure yours would be the same deal, do you have a manual?)

 

[Bannister 6905]

Thanks, everyone, for your comments.
Today, I did the following:

* checked electrical connections at the voltmeter and tach - all OK
* removed and cleaned the pulse limiting valve - replaced line
* rebled the oil injection system, including flushing the pump with solvent, cleaning the filter screen and check valve
* checked connection from VRO pump to engine harness (OK)
* confirmed that the warning horn went off when the harness was disconnected

The result of all this work was a working VRO!!! I suspect there was additional air in the supply line, along with a small leak in the pulse line. It also seems there was a film on the screen filter that may have been restricting oil flow.

Consider this issue resolved!