CONTINUOUSWAVE

I have a 1993 Yamaha 70 HP outboard. When [the engine crankshaft speed exceeds] 4000-RPM, an aural alert sounds. If [the engine speed is reduced to] about 1500-RPM [while the engine remains] in gear [for] a few minutes, [the aural alert] [stops]. [The engine has a] temperature gauge that is accurate, and it reads about 135-degrees-F.

[Sometime after observing the behavior described above] I replaced the [temperature] sensor in the cylinder head with a new OEM sensor. Now, when I turn the ignition key switch to ON, an aural alert sounds. [This sounding of the aural alert] didn't [occur] with the old [overheat sensor].

Anybody got any ideas?

Does the aural alert shut off after a few seconds? Most are designed to test themselves when you first turn on the key.

No. [The aural alert] continues to sound until the ignition key is turned to OFF. [The aural alert] continues to sound when engine is running.

Ole betsy wrote:Anybody got any ideas?

Here are my ideas. In any alarm system, when the alarm is sounding there are three possible situations:

--there is an alarm condition, the condition has been properly detected, the alarm is sounding to warn you of the alarm condition; everything is working properly in the alarm system, and there is something wrong with the device being monitored (i.e., the outboard engine);

--there is no alarm condition, a sensor or detector has made a false reading, and the bad sensor causes the alarm to sound; nothing is wrong in the device being monitored, but something is wrong in the alarm system, one of the sensors is bad; or,

--there is no alarm condition, no sensors are bad, the alarm itself is malfunctioning and sounding inproperly; there is nothing wrong in the device being monitored, there is nothing wrong with the alarm sensors, it is just the alarm itself that is bad.

By being aware of these three conditions, and having knowledge of how the alarm system works on a particular outboard engine, such as a 1993 Yamaha 70-HP, you can investigate the alarm sounding problem and deduce which of the three scenarios is taking place.

Clearly if the alarm sounds when the engine is not running and continues to sound even when the engine runs without overheating, the most reasonable deduction is either the second or third situation exists, that is, there is something awry in the alarm system, not in the actual engine operation.

Usually the alarm systems on these older outboard engines will sound their aural alert for several possible causes, and often a difference in the cadence of the alarm must be interpreted to understand the cause.

Typically a continuous sounding of the aural alert indicates an overheat condition. The operating instructions or owner's manual or owner's guide for your 1993 Yamaha 70-HP engine will clearly describe the possible causes of an aural alert to sound, will offer advice on what action to take immediately, and also offer advice on a remedy to the problem.

What does your operating guide say?

Please list the conditions that the aural alert on a 1993 Yamaha 70-HP engine can signal as being out of normal according to the operating guide.

Ole betsy wrote:...I replaced the [temperature] sensor in the cylinder head with a new OEM sensor.

That you replaced the temperature sensor in the alarm system with an OEM part is good, but did you replace it with a direct replacement part? Perhaps you bought the wrong sensor. Perhaps you incorrectly installed the sensor.

Typically the temperature sensor for an alarm system is a thermally-operated switch. The switch action is usually normally-open and the switch closes when a temperature threshold is exceeded. If you replace such a sensor with one that has the opposite action, that is, a normally-closed sensor, you will get a continuous sounding of the alarm until the engine temperature exceeds the threshold and the switch opens. This is, of course, of no value as an alarm indicator.

Often with a temperature sensor switch, the engine block become one part of the circuit. Check that there is good electrical contact with the engine block at the switch sensor.

Proper part was purchased and is installed properly, also block does not serve as ground, sensor is rubber grommet mounted, using two wires. Maybe I didn't say this before I removed the sensor and the buzzer still stays on. Anybody got any ideas. When you turn the key on with sensor removed and disconnected, the buzzer is on until you turn the key off. So now the sensor is eliminated. Still looking for ideas

All you know by disconnecting the temperature sensor is the temperature sensor is not affecting the alarm state.

Do you have the operator's guide? Can you provide the information from the operator's guide I requested earlier? What conditions signal an alarm?

Have you checked the level in the oil tank? Have you checked to make sure the filter on the oil pickup is not clogged? Most operating guides for a Yamaha 70-HP of that epoch indicate that the aural alert will sound continuously if the oil reservoir is low or the filter is blocked. This information is right in the operating guide for the engine. Do you have the operating guide for your engine?

Two conditions in your model normally sound the alarm and put the motor into the RPM reduction mode. A switch closing in the oil sensor assembly or a switch closing in the thermoswitch assembly.

If the switch in the oil tank is open (normal condition with sufficient oil) and the thermoswitch switch is open (normal condition) then I would suspect a faulty wiring condition. We can rule out the thermoswitch as being the problem since you say the horn sounds even with the switch completetely removed.

I take it you do not have a Yamaha multifunction tachometer installed since it would tell you if it is oil related or temperature related.

If you confirm the oil sensor works normally the next step is to check the wiring. The horn will have 12 volts to it when ever the key is on. If either the pink wire from the thermoswitch chafes to a ground, or if the wire from the oil tank switch chafes to a ground, the horn will sound. The motor will put itself into RPM reduction mode.

Check those wires for continuity to ground.

Well the motor sat for a while, I told my son , we are going to fix the motor one way or the other. The other meaning if we can' t find the short to ground we would eliminate the buzzer and disconnect the wire to the cdi box that reduces the rpms. I would do this if needed because I have an accurate temp gauge on the console. We go to check the motor an my son says I know what's wrong, I say sure you do, like how would he know what's wrong by just walking to the back of the motor, well he saw a black wire with white stripe with #1 connected to the temp sensor and a black with white stripe connected to the top coil. He switched the two and said go turn the key on, I did and bingo no buzzer sounding, sure enough he fixed the motor. Turns out the one with #1 goes to the #1 coil, the other to the temp sensor. This called for crawfish boil, so we boiled some crawfish.

According to the YAMAHA WIRING COLOR CODE, see

http://continuouswave.com/whaler/refere ... e.html#Yam

a BLACK with WHITE STRIPE wire is associated with the primary winding of the ignition coil. As you described, this wire should go to the ignition coil primary. (You mention this wire has been marked with a "1", corresponding to the coil number.)

A BLACK with YELLOW STRIPE is associated with the temperature sensor. You describe this wire also being Black with White stripe. This does not conform with the color code standard.

Check those two wires carefully. Perhaps the BLACK with YELLOW STRIPE has fading in the color and the yellow looks more like white now.

If you connected the warning system BLACK with YELLOW to the ignition coil primary, the low resistance of the ignition coil winding would be almost a dead short to ground, causing the alarm to come on. The cylinder for the coil would have no spark. The three-cylinder engine would have been running on only two cylinders.

If you connected the ignition primary circuit to the alarm system, you would have been feeding a high voltage into the alarm system, which could cause some harm. The primary coil voltage would only be present when the engine was running. If you never started the engine while this circuit was mis-wired, then no harm would occur.

The most interesting question from all of this: who switched the two wires to cause the problem?

Today, with everyone owning a modern color digital camera, before disassembling anything, take several pictures of the device before taking it apart. These digital images will be very useful in putting the device back together.

Better buy your son something extra; he saved you from a lot of expense getting that engine running.