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Need Help Identifying A Mercruiser 4.3L Component (Sensor / Switch)

J

_jp

Contributing Member
Hi

While trying to diagnose a problem with my (recently new to me) Mercruiser 4.3L (Serial No: 0W034153), I came across a rusty looking sensor / switch hidden between the distributor and the coil area at the back of the engine. It has a brown and a colour stripe (can't make out the colour though) wire and the current connector looks to be a previous repair job.

Most components I have managed to work out now, but could someone please educate me as to what it is? Also, there looks to be a rusty two-pin electrical connector fixed to the engine next to it as well; if anyone knows what that was for - guessing an "optional" item?

Thank you

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kghost said:
Oil pressure sender.
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Ah, now that's interesting, thank you. I thought the Oil Pressure Sender was somewhere else (near the filter from what I had read) and thought this might be temperature related. Seeing as I've got Carb flooding issues, that could well be part of that problem. By the state of how it looks it needs replacing.
 
kghost said:
here is the correct schematic for your model/serial.

View attachment 36256
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Thanks for taking the time to check that out. If it's just the alarm, then I won't worry so much. But, I will test it next time I'm working on the boat to see if the alarm sounds - the alarm is another item I need to locate lol. As the switch is a single wire, which I think is Tan (but not sure on the stripe colour), I would guess it simply grounds out to activate the alarm.
 
What would happen is, when key is turned to run position, alarm would sound as there is NO oil pressure. To test it would be to ground wire thats connected to the oil pressure switch. It should just pull off sensor if not held by a nut. If a nut, remove nut then wire. Then touch wire lead to ground. It should cause an alarm.
 
_jp said:
Thanks for taking the time to check that out. If it's just the alarm, then I won't worry so much. But, I will test it next time I'm working on the boat to see if the alarm sounds - the alarm is another item I need to locate lol. As the switch is a single wire, which I think is Tan (but not sure on the stripe colour), I would guess it simply grounds out to activate the alarm.
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Remove it and look at what's on the end that was in the engine- if it's oil, use a vacuum/pressure gauge and see if it makes noise without pressure and if it stops when you pressurize it. That tells you it works, but nothing about activating at the correct pressure.
 
Thanks @kghost and @jimn for the additional info. The main thing for me at this point in time is to rule out any potentially impacting issue with the fuel pump and carb; as I am aware that side is related to oil pressure.

It's the Carb i have an issue with (on a separate post, which is majorly flooding). If this switch just sounds an alarm, then I can rule that out and i'll try and check if the alarm works at least (removing the cable and grounding it as per @kghost). I understand that the pressure check may not be accurate from the switch itself and I think i'll just replace it regardless, but thanks for highlighting that too @jimn.
 
Your fuel system also uses a oil pressure switch. It is typically located near oil filter lication (lower side of passenger side of engine. This pressure switch has NO alarm. It is designed to stop fuel pump if you loose oil pressure. It is wired into fuel pump curcit . So also because there is no oil pressure if you only turn key to on position, the fuel pump wont run. The cranking curcit allows power to pump, which in turns creats oil pressure during cranking, then once engine starts and key is returned to on position, pump remains running as needed. (Basically pump only works when engine is running or cranking)
 
kghost said:
Your fuel system also uses a oil pressure switch. It is typically located near oil filter lication (lower side of passenger side of engine. This pressure switch has NO alarm. It is designed to stop fuel pump if you loose oil pressure. It is wired into fuel pump curcit . So also because there is no oil pressure if you only turn key to on position, the fuel pump wont run. The cranking curcit allows power to pump, which in turns creats oil pressure during cranking, then once engine starts and key is returned to on position, pump remains running as needed. (Basically pump only works when engine is running or cranking)
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Thanks, that makes sense. If the engine was to stall and cut out, but the ignition left on, would the fuel pump typically still run on do you know?
 
If there is no oil pressure for what ever reason including engine stalling/cutting out there will be no oil pressure therefor No power to the pump (even with key in the run position) and the pump will not function.
Once you start to Crank the engine over that power comes from starter solenoid and powers fuel pump.
 
kghost said:
If there is no oil pressure for what ever reason including engine stalling/cutting out there will be no oil pressure therefor No power to the pump (even with key in the run position) and the pump will not function.
Once you start to Crank the engine over that power comes from starter solenoid and powers fuel pump.
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Thanks for clarifying 👍. I wonder if the previous owner has modified the sequence, I am pretty sure that I could hear the fuel pump (or something else similar - presumed it was the fuel pump) running after the engine cut out last time I got it to start.

I did take the tan and blue wire of the oil alarm switch and put it to ground with the ignition switched on and there was no alarm. Do you know where the alarm is, or places to look on a Mercruiser 4.3L?
 
_jp said:
Thanks for clarifying 👍. I wonder if the previous owner has modified the sequence, I am pretty sure that I could hear the fuel pump (or something else similar - presumed it was the fuel pump) running after the engine cut out last time I got it to start.

I did take the tan and blue wire of the oil alarm switch and put it to ground with the ignition switched on and there was no alarm. Do you know where the alarm is, or places to look on a Mercruiser 4.3L?
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The engine/drive manufacturer isn't usually the source of the alarm buzzer, that's usually part of the harness installed by the boat manufacturer and they usually put it under the helm. It's often similar to the part in the photo- doesn't matter if it looks the same as long as it does the job. It's usually a piezoelectric buzzer.

Don't be too surprised if it has been removed, a wire has been cut or it has been covered with tape- I have seen those on boats and read recommendations to cut the wire on a boat user forum.
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Thanks @jimn. Would the other warning switches (e.g temperature switch) also use the same alarm? I'll check under the dash when next on the boat to see if I can find it.
 
_jp said:
Thanks @jimn. Would the other warning switches (e.g temperature switch) also use the same alarm? I'll check under the dash when next on the boat to see if I can find it.
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You mentioned the serial number being wrong- isn't it on the plastic cover for the flame arrestor? Could a character be missing from the serial number?
 
_jp said:
Thanks @jimn. Would the other warning switches (e.g temperature switch) also use the same alarm? I'll check under the dash when next on the boat to see if I can find it.
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Only one alarm sounder. All alarm device at engine are part of One curcit. So any one would cause the same alarm. Basic alarm system. Pre computer type systems.
 
kghost said:
Only one alarm sounder. All alarm device at engine are part of One curcit. So any one would cause the same alarm. Basic alarm system. Pre computer type systems.
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Thanks @kghost, that helps a lot👌 - i'll follow the Tan & Blue Striped wire and see where it takes me lol. The serial number is the correct one @jimn, but as it's old (1996 ish) I don't think it comes up in all databases - perfprotech it comes up.
 
_jp said:
The serial number is the correct one as it's old (1996 ish) I don't think it comes up in all databases - perfprotech it comes up.
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Just wondering what year is the boat? From memory, your engine serial number of 0W0 (0W034153) should put the engine year right in the 2004ish year range.
Your model number that comes up against your serial number is 4211035RS.

The following is a engine parts catalog for the serial number in question from this website,
 
That's my bad @Fun Times! It is, or should be a 2004 ish. 1996 is the Mercury 115 outboard on our family's boat. Tired eyes and brain at the moment... Well spotted!! Thanks for the link!
 
Slightly off topic, but do you know what section of the Marine Engine parts catalog that Earth Grounding Posts would come under @Fun Times? I've cleaned mine up as much as possible, but wondered if I can get replacements?
 
Often you’ll find the grounding wires for/from the battery and the engine wiring harness smaller connections starting off at either one of the main two studs of either side ‘at the rear of the engines flywheel housing or anyone of the bolts holding the housing on too… so either item number's 24 or 20,

But they are usually not bad enough to need new though but also make sure paint isn’t affecting them as well as corrosion.
 
Fun Times said:
Often you’ll find the grounding wires for/from the battery and the engine wiring harness smaller connections starting off at either one of the main two studs of either side ‘at the rear of the engines flywheel housing or anyone of the bolts holding the housing on too… so either item number's 24 or 20,

But they are usually not bad enough to need new though but also make sure paint isn’t affecting them as well as corrosion.
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Thanks for taking the time to source that, it's #24 I would be after. I'll try cleaning it up some more first, just quite difficult being right at the back. Thought removing it and replacing it ight be easier.
 
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