4.3L mercruiser engine

Attempting to find the wiring diagram for this? I have looked around and can't find the plug that would is supposed to go in there. Any assistance to point me in the direction of it would be greatly appreciated as I'm running into the issue below.

I am getting a single beep alarm at idle and under load at approximately 3000 rpms. At first when the boat was started I was getting multiple single alarm's in a row. Then, under load at 3000 rpms it beeps once multiple times in a row. I then met up with a friend in the middle of the lake and sat there with the boat running for close to 25 minutes in neutral and didn't get a single alarm. When I left and opened it up to 3000 rpms, I would get the single beep multiple times in a row again. I am baffled.

Would the plug missing cause this? I've had a mechanic check it out and everything checks out mechanically and I have vessel view attached and not getting any error code for oil sensor, water pressure sensor, or temperature.

What year is the engine?
That is the camshaft sensor and it wasn’t used until starting about 2006… of it was plugged in at one time and someone unplugged recently then yes it would sound the horn but the engine would run very differently if at all.

You’re most likely going to need to get the engine scanned with a scan tool of sorts to try and find out why the engine’s warning horn is sounding off at 3000 RPM.

There’s a couple of eBay sellers that do rent out software to be able to scan your own engine vs going to a service dealer… that or you could buy your own scanner as well if desired.

2007 engine. Engine has been scanned with a scan tool. Everything checks out. I am trying to find where I would find the plug that goes into there. I can't find a wiring diagram, which I am trying to find for the plug

Nord2903 said:

2007 engine. Engine has been scanned with a scan tool. Everything checks out. I am trying to find where I would find the plug that goes into there. I can't find a wiring diagram, which I am trying to find for the plug

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Thinking back, i believe it was the v8’s that first used the cam sensor first and a long delay in the v6 engines.

In 2007+ Merc stopped putting wiring diagrams in service manuals and went to wiring harness paper type binders and made separate ones for individual engine models.

Here’s some examples, this may or may not be for your engine model but seems close,

More in here,

I’d say reach out to MerCruiser customer service with your engine serial number by send them an email asking what the part number is for your diagram and usually they will respond back with something.

So I connected my vessel view and ran it under load and took multiple snap shots. I am getting an alarm at idle when I first start the boat and again above 3500 rpms. The oil temperature and engine temperature, I believe are very low. The other concern is the water pressure is also very low while under load. Would appreciate any insight.

Yes it seems the water PSI is way to low...So maybe a clog someplace, bad impeller or worn internal housing or failing sensor....Being I'd tend to believe you have an Alpha stern drive? In your case I think I'd start towards inspecting the water pressure sensor which may be mounted near/on the power steering cooler...Item number 16, https://www.mercruiserparts.com/bam/subassemblydetail/43948594/28193445

Pull it and clean it possibly...

Fun Times said:

Yes it seems the water PSI is way to low...So maybe a clog someplace, bad impeller or worn internal housing or failing sensor....Being I'd tend to believe you have an Alpha stern drive? In your case I think I'd start towards inspecting the water pressure sensor which may be mounted near/on the power steering cooler...Item number 16, https://www.mercruiserparts.com/bam/subassemblydetail/43948594/28193445

Pull it and clean it possibly...

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Yes, the water pressure is way too low, what doesn't make sense is that if the water pressure sensor is faulty, I would expect that it would throw a code and that the engine temperature isn't anywhere near what it is supposed to be. Which is throwing me for a loop. I ordered a new water pressure sensor, but again it doesn't make sense.

Some of the other readings don't make sense, your engine temp is very low, yet water pressure is also low, with low water pressure you might expect the engine temp to be too high....

exactly! unless the thermostat is stuck open. But shouldn't a code by thrown for that as well?

Nord2903 said:

exactly! unless the thermostat is stuck open. But shouldn't a code by thrown for that as well?

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No, there's no fault code for a cooler running engine that is still within a programed temp range... If that temperature is the temp for after roughly 8 minutes of engine running time at idle, then yes most likely the thermostat might be stuck open either by age, corrosion, and a bit more common 'debris such as rocks/sand and if that may be the case of debris, then maybe the water sensor needs a cleaning as well.

A too low of water pressure would sound the warning horn especially over 3000 RPM...The ECM knows a general range it should be at all RPM's and not necessarily throw a code per se... without one of us from iboats forums being there to help you check it out better, I'd venture to say low water pressure "readings" could be the issue of the alarm even if the engine is not running hot because the sensor thinks it's low when it may not be low...It's time to pull things apart to inspect, back flush then order parts as found needed possibly such as an impeller and related gaskets and impeller housing cover, (< Alpha drive right?) gear oil and a oil fill pump kit, water psi sensor since you already ordered one, MerCruiser 160 degree thermostat kit and maybe a stern drive install gasket in case you have to remove the drive to inspect the water inlet hose area for debris stuck or even just because it's time?

If you're going to be doing your own work and pulling the drive off for general services (and beyond) then you're going to need an alignment bar at minimum so I'd recommend picking an more affordable tool kit that offered the most tools to work in the drive/transom area for the lowest costs possible as maybe someday you or a friend may need them.

seeing that, id want to take readings with an IR temp gun,,,,

Lou C said:

seeing that, id want to take readings with an IR temp gun,,,,

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Just purchased one, the water pressure sensor is going to be replaced as well as the thermostat with the other one being tested when removed.