Mercruiser alarm stopped working, kind off

[nennedk]

I have a Mercruiser 5.0L carbed engine from 2002 where the alarm buzzer suddenly has stopped working. When I put ignition on it wont go on as it used to. But when the engine is running and I ground the drive tube it goes on, and also when i ground the oil level sensor. So it seems that it's just the start alarm that dosn't work.
I have read the volts at the buzzer and it seems strange to me. With ignition off it reads -0.31v, with the ignition on, but not a running engine it says 0.74v and last with the engine running it reads 1.43v. Can anyone point me in the right direction. Thanks

 

[alldodge]

The standard non-EFI motor which has a carb has 12V going to the buzzer from the ignition wire (Purple)
The other side of the buzzer is Tan/Blue and goes to the different switches and the buzzer will sound when one is grounded.

Normally the buzzer turns ON when the key is turned to ON because the oil pressure switch is closed until the motor is started.

Merc does make a timer which is on the buzzer which delays the turning ON for so many seconds. Don't know if yours has one or not. In any case you should see more then 1.43V with the key ON, and nothing with it OFF

 

[nennedk]

Theres no delay for the buzzer. It used to buzz when i turned the key on, and as soon as the engine was running it kept silenced.
Can anyone confirm that the sensor sitting on top, back, port side, between the ignition coil and distributor and has a tan/blue wire is the oil sensor. If it is, isn't it strange that the buzzer works when i ground it, but not when turning key before engine running?

 

[alldodge]

All Tan/Blue wires go the the ground side of the buzzer, so grounding it will turn on the buzzer.

Question: does the sender your discussing look the first or the second

If it does look like the first one, then you just need a new switch, of the threads on the switch are not making contact with the block

Oil Pressure switch



Oil Pressure gauge sender

 

[achris]

The 'key on' buzzer test is generated in the ignition module. If it's stopped working, your problem is in the module. That module also relays the over temperature alarm. Ground that switch and see if the alarm sounds....

Chris...........

 

[nennedk]

"Question: does the sender your discussing look the first or the second"
my switch with the tan/blue wire looks like the first picture

"the over temperature alarm", is that the one with the yellow wire connected at the thermostat house? I will try to ground that the next time i'm at the dock

Not happy to hear it's maybe the ignition module....

 

[alldodge]

The oil pressure switch is the first pics

"the over temperature alarm", is that the one with the yellow wire connected at the thermostat house?

I'm at the point I need either your motor serial number of a pic of your carb. If you had a carb the water temp alarm should be Tan/Blue and not Yellow. If its solid Yellow then you probably have a TBI

 

[achris]

I have a Mercruiser 5.0L carbed engine from 2002

Not EFI... I was a little out with my assertion that it was the temperature sensor that is relayed though the ignition module... That was for engines up to 2001, as you have a 2002, it is slightly different. It's now the oil pressure switch that is relayed though the module, not temperature. Regardless, the problem remains the same...

Here's the wiring diagram that should be for you engine...

 

[nennedk]

I dont have a TKS engine. This is my engine serial: 0M359543. The boat is a Rinker 232cc from 2002.

At the thermostat housing I see 2 switches, one solid tan and one solid yellow

 

[nennedk]

I think this picture shows my wiring diagram.

- turn key - no alarm (used to sound the alarm)
- with engine running and grounding oil pressure switch (C1) the alarm turns on
- with engine running and grounding gear lube monitor (C2) the alarm turns on

i haven't tried grounding the water temp switch (C3) but i will next i'm at the boat

Can i conclude anything from above?

 

[alldodge]

Yep, 2 bbl carb and Yellow goes to ignition module, and the Tan/Blue that would have goes straight to the switch also goes to the module

 

[achris]

...Can i conclude anything from above?

Yes, by that diagram, your engine is 2001. The boat may be 2002, but not the engine.

So yes, you have the temperature alarm going through the ignition module.

 

[nennedk]

Went to boat today and grounded temp switch (yellow wire) with key on, engine not running. It sounded the alarm. So don't you think I should replace the water temp switch, part No. 805218T, or could it still be the ignition module?

 

[alldodge]

Went to boat today and grounded temp switch (yellow wire) with key on, engine not running. It sounded the alarm. So don't you think I should replace the water temp switch, part No. 805218T, or could it still be the ignition module?

Not necessarily, if the motor is not overheating then the alarm should not sound. Put the sensor in a pan of water on the stove with a thermometer. Connect a ohm meter to the leads, then heat the water and see if it closes contact when it reaches above 190 degrees or so

Your thread started with saying the alarm stopped when key is turned ON. This was determined to be a bad oil pressure switch.

 

[nennedk]

Sorry if haven't explained my self well. (i'm danish ). Just to clarify the issue.
The alarm used to sound when i turned the key ON, but silenced as soon as the engine was running.
Now the alarm doesn't sound at all. (unless I manually ground the switches)

"The 'key on' buzzer test is generated in the ignition module. If it's stopped working, your problem is in the module. That module also relays the over temperature alarm. Ground that switch and see if the alarm sounds...."
I did and the alarm sounds....?

 

[alldodge]

Agree no alarm unless the switch is grounded. Through your testing, I see that the reason the alarm does not come ON when the key is turned ON, is because the oil pressure switch (one in first pic) is not working. The oil pressure switch should be located below and behind the distributor, and if not there port side where the remote oil filter adapter is (has one Tan/Blue wire).

I this switch is replaced the alarm sound sound when the key is turned ON

 

[achris]

Agree with AD, oil pressure switch needs replacing.

 

[nennedk]

Okay, thank you both, I will order and replace the oil pressure switch and report back.

 

[nennedk]

While I'm still waiting for oil pressure switch delivery, I was looking at my SERVICE MANUAL NUMBER 24 for instructions to change it. But the manual doesn't tell anything about it, only how I test it. Can anyone tell me where i could find instructions for changing it. Thanks

 

[alldodge]

Remove plug off it.
Install socket over sender and unscrew. Reinstall new one and snug it up, does not need to be real tight. If after running it is slightly leaking, give it 1/4 turn more