1989 Merc V150 No Alarm Beep

[Dukedog]

Ya gotta have 12V on purple when key is on for module to operate....If it don't self test the module is bad and this is a very common problem.

like he says.. 12v on purple or tan/purple (module) at key on and no "self check beeps" module is bad.............

 

[sam am I]

12 volt power is getting to the purple wire on the alarm module. .

and hooked up the replacement module with the same results, no beep. .

like he says.. 12v on purple or tan/purple (module) at key on and no "self check beeps" module is bad.............

Lol, take two!......OP has reported in his first post that he did check and has 12V on purple and that he has swapped out his alarm module once already...............See his quotes above and in #22 that he posted waaaaay back from #1

He may have a bad second alarm module but, doubting it....

 

[sam am I]

Should be close, I'll scope the levels soon, snow permitting.

 

[Faztbullet]

Good post if you want to do technical and in-depth troubleshooting....But to keep it easy for us simple people...start motor, disconnect rotational sensor wires...no alarm module bad. Reconnect and restart and remove oil level float wires...no alarm module bad. Reconnect and pull green wire from module to cyl #5 and restart...no alarm module bad. Some of the above testing will take several minutes for a result

 

[sam am I]

The alarm module is a state machine.....

So without proper initialization (you hear the power on beep sequence), preforming those(any) tests with it will give false negatives.

i.e., The module will remain forever in its first state (NOT BROKE) until you get it to initialize properly.......It has to see expected value/s upon power up to go into its next/final state of functional else...STOP!!.

Doing any testing with it and making conclusions on how it did or did not react without FIRST hearing the power up beep sequence is pointless, it's not getting to that state.

No power up beeping means simply three things........

1) Beeper bad (checked)

Moving on........

2) Module bad (he's swapped one out already).........

Moving on........

3)Sensor level bad (bad/broken sensor, connectivity, supply voltage)

We're here now, checking things off the list.....Not so complicated? For even for "simple people"?

 

[Dale Lee]

Here are my test results from Sam's detailed recommendations. Ignition ON - 12v. on purple wire and white wire on alarm module. Crank test - .Ig. ON either 0v. or .5-.6v. on blue/white wire connecting motion sensor to module, presumably dependent on the position of the magnet. Cranking results in the intermittent .5v which lasts for 11/4 revs then drops to 0v. for 3/4 rev then goes back to .5v. I pulled the motion sensor and get .5v, while moving a magnet over it drops it to 0v.

I repeated the tests with the used replacement module. Ignition ON - again got 12v. on both the purple and white wires. This time I got 0v. or the full 5v. on the blue/white wire repeating the same cycle as above. Ig. ON is either 0v. or 5v. depending on the position of the magnet (I assume).

Another observation is that it appears that .5v or 5 volts in the blue/white wire (original vs. replacement module) is coming from the alarm module and not from the sensor. When the blue/white wire was unplugged from the sensor there is a constant .5 or 5v. coming out of the blue/white module wire again depending on which module is being tested. This also seems to be supported by the fact that passing a magnet over the unseated motion sensor causes the voltage to be "switched off" to 0v in both modules.

Conclusion: The motion sensor seems to be cycling properly. Do you all agree?

Since I still have all of the plugs pulled and the weather is crappy I haven't been able to perform the tests with engine running as suggested by Faztbullet. I will try to do those sometime this coming week.

It does appear that my original alarm module is faulty since it never feeds anything close to 5v. to the motion sensor.
The fact that the replacement alarm module does not trigger a beep with the Ig. ON seems to support that it is faulty as well but with a different problem since it is passing 5v. to the motion sensor. I suspect that the tests with the engine running will support this. Any other comments or suggestions?

The replacement alarm module is used so it is entirely possible that it has failed as well. Fortunately it has a 1 year refundable/replacement warranty which is the only reason I bought it.

Thank you all for your suggestions in helping me diagnose the source of the problem. This motor is 31 years old and has run perfectly for the 25 years I have owned it. My only expense has been two oil caps and normal maintenance so $350 for a new alarm module will be worth it if that is what is needed.

 

[sam am I]

With these results, Agreed!

Original module (low of 0V okay BUT 0.5V for a high level not good, should be around 5V and has no power up beep)

Replacement module (0V low okay and 5V high okay, however still no power up beep),

Both those results alone, one s/could conclude, yes, two bad modules(although one runs the sensor properly) and a good sensor. Bonus......and the oil injection system is good too!!

 

[Dukedog]

his "second" module was used from internet so take a guess... "it worked fine when we took it off tha motor".

 

[Dale Lee]

The failure of the replacement module may be the whole reason the motor is being sold for parts. Thankfully the seller offered the 1 year warranty since they couldn't bench test it.

Thanks to you all for your comments and suggestions, especially to Sam who sent all of the details. I'll post again when I get it running with the new module installed.

 

[sam am I]

No problem Dale, glad it got down to perhaps a 99% for-sure on what to replace......Hate to just throwing money and just hoping it fixes it, I'm with you on that!!

Also thanks to you for closing this up when you get a chance, it truly helps others so much more to know where and how it played out.

 

[Dale Lee]

Beeep, beep, beep! I finally installed the new alarm module and I get the ignition ON beep sequence. Sounds great but it's obviously the only time I want to hear it! I ran the tests Faztbullet suggested with the engine running and it all checks out. I first ran those tests with both my original and the used replacement alarm module. Mine failed on both the oil cap and motion sensor tests. The replacement failed on the oil cap test but worked on the motion sensor test. I got a refund on the replacement from http://www.southcentraloutboards.com/ and I didn't need to send the part back. I did send them the details on my testing. They mainly sell used parts and are an honest business with good customer support. They didn't make any money from me this time but I will sure consider them in the future.

Thanks gents for all of your advice. I learned a lot which is difficult at my age. Stay healthy and be safe!