Mercruiser 3.0 MPI ETC, Oil pressure sender issue? I can't find it.

J

javabeaver

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Boat dead when idling in water. Had to tow it back.
Turn key to run position, no beep. Normally it would give a long beep. Then I would start the engine. Now when I turn key to start, engine would crank but wont' turn on. Not battery issue. Charged battery, and also tried two car batteries. Oil pressure gauge only moved slightly when turn key to run. Other gauges appears working fine. Measured at the key starter, the wire from engine had voltage of 3V to 0.8V, not stable. The print on the beeper shows voltage 5V to 15V to sound. I connected it to a 9V battery, made constant sound. It looks like problem is with oil pressure reading.
Spent more than 2 hours around engine, couldn't find the oil pressure sender. Tried to find the service manual, but couldn't find one for the exact engine I have. I must have a weird engine.
I did find some information of 3.0L Mercruiser, but apparently it was for 3.0 TKS. The oil pressure sensor would be between the oil pump and starter. But the engine I have is 3.0 MPI ECT. No oil pressure sensor at that spot.

I would really appreciate anyone could point me where the oil pressure sender is. Or if there is any other test I could do.

Engine: 2012 Mercruiser
Information from the sticker on top of the engine.
Model: MCM 3.0 MPI
Displacement :3.0L (181 CID)
Engine rotation: LH
Engine Serial number: 2A04####
 
Fun Times

Fun Times

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Because you have no beep at first key up like normal on an MPI engine would indicate you have lost 12 volt power most likely to the ignition circuit which should be pointed to purple wire you may see off the back of the key switch or maybe the red wire there too but doubtful because the engine cranks over it seems you've mentioned.

The MPI's don't rely on the oil pressure circuit to start the boat and if the engine didn't start then the oil psi isn't really going to go up much while just cranking over the engine for a bit.

What does the 12 volt gauge say?
Since you seemed to have checked the 12 volts at the Key switch? and only received voltage of 3V to 0.8V, then that is to low because the battery should be about 12.6 volts engine off and around 13.8 engine on.

You might have even lost a ground wire/battery cable connection someplace too... With the key on try carefully wiggling wires around and see if the horn will turn on for 2 seconds and the 12v gauge goes up if it's low/at rest?

Also make sure the safety lanyard switch is up/on at the shifter control unit by physically exercising it a few times and turning it on as that switch turns off the ignition circuit.

3.0L MPI EC - 1A072812 & Up

3.0L MPI EC - 1A072812 & Up
www.mercruiserparts.com www.mercruiserparts.com

Electrical Components

Electrical Components
www.mercruiserparts.com www.mercruiserparts.com
 
J

javabeaver

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Thank you so much. That may explain why I couldn't find the oil pressure sensor. Wish I came here asking earlier. wouldn't spend those time trying to find a non-existing oil pressure sensor.

I did check the key wire a bit yesterday. It has three connectors, B (red wire), S (Yellow and red wire) and I (purple wire). When I turn key to run position, the light on all the gauges in the panel came on. So I assumed they received power.
I'll work on the boat in a couple of hours. I will measure the voltage of the 3 connectors at the key, also test the wire connection as you suggested. Then I'll report back .

Yesterday the first thing I checked was the lanyard switch. when the switch was closed, I measured 0 resistance. I also unplugged the wires and shorted them, same problem. I assumed it was not the lanyard then.
I checked all the fuses I could find, 2 at the batters, a bunch in the box under the console, and several at engines. Didn't find any of them brunt.
 
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J

javabeaver

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I did some more tests.
The key switch does get 12V, and it functions normally. When the key is turned to run position, the 12V (from red wire) is delivered to the beeper (on purple wire). If I turn the key to start, 12V is delivered to yellow wire and engine will crank.

The other wire connected to the beeper is a brown wire, going into a pretty big cable and goes back to the engine. I measured it, it is open to both ground and 12V. That's why no beep.
I tried to wiggle a lot of wires with the key in run position, but no beep sound.

The beep is supposed to indicate passing a self test. Now it doesn't beep, that probably means the engine failed a test and so the brown wire circuit is open. If it's not the oil pressure issue, it probably is fuel problem. Now I recall when everything was working, if I turned key to run position, the engine would make small noise then the beeper will sound. I assume it was the fuel pump noise. Now when I turned the key, it's dead silence.

It's quite likely there is something wrong with the fuel delivery system. It also explains why the engine would crank strong, but won't start. I took a picture of the fuel pump (pardon the bad quality). I think it's a electronic pump. But I couldn't find a single wire going to the pump.
Any suggestion on how to test it if suspect fuel delivery problem? Many thanks.

I also have another problem I don't think it's related to this, but just in case it may provide any clue. The engine trim gauge quit working more than 1 year ago. Light still comes on, but gauge always shows trim is all the way up. The trim works perfectly. I always drive with trim fully down and move to full up before I pull the boat out of water, so I didn't really need that gauge. Didn't bother fixing it.
 

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Fun Times

Fun Times

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You have 2 fuel pumps... 1 is mechanical (your photo) for low psi and the other is electrical for high psi... Item numbers 6 and 10, https://www.mercruiserparts.com/bam/subassembly/30916/13809/60
Here's the inside of the high psi pump, https://www.mercruiserparts.com/bam/subassembly/30916/13809/70

It still sounds like the ECM is not "waking up" via 12v power of the ignition circuit as the ECM should send a 2 second fuel pump prime when first turned on which includes the beep.

Maybe the power relay item number 13 has gone bad in some way, https://www.mercruiserparts.com/bam/subassembly/30916/13809/40

Try lightly "tapping" on the relay a few times as it is mechanical inside to see if the ECM will wake up...
Also check power and grounds all over the engine.
Also just for reference item number 38 might be your engine oil psi sensor...881879T11 Pitot, Oil Pressure Sensor (0 - 100 PSI).

Own a ignition timing light? If yes put it on either the main coil wire or a spark plug wire and crank over the engine watching to see if the light flashes… Thinking you may not have spark either.
 
alldodge

alldodge

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Need to fix the kink in the fuel line. Might see if it can be turned another 270* so it points side ways and straight out. This will provide enough room to keep the kink from happening.

On the same subject, the fuel line is fairly skinny and doesn't look like USCG type A1. See if you can find type A1 stamped on the line. If not and if you can only find something like 3/8 gas or fuel line, then the folks installing the motor used the wrong hose.

There will be relays on the motor and one of them is the Main Power Relay (MPR). Another is the fuel pump, and if there others may be for start assist. My point is with your hand on the relay, turn key ON and fell for a click.

Oh looks like FT just responded

If no click double check the fuses near by
 
J

javabeaver

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Apr 24, 2014
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Thanks Fun Times and alldodge. A lot to check tomorrow. Need to fine the main power relay and the fuel pump relay first. Is there a service manual for my engine? A wiring diagram could be very helpful. The one I found had oil pressure sender, so it's not for my engine.

The boat has been used like this for 8 years. Never touched the fuel line. Don't think that's the cause. But tomorrow I'll temporarily hold the line to remove the kink and ask wife to turn key. Will take a closer look at the fule line and see if it should be replaced or turn that tube horizontal after fixing the starting issue..
 
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