2001 Merc 350 Oil Pressure Switch Location
 

Trying to fix my engine alarm going off.
I now understand the engine has two oil 'sensors'.
One feeds the dash gauge - sender
One feeds the ECU - switch

I have MEFI3

Where is the one that feeds the ECU located? I think to test I pulled the wire off the wrong one.
The one that feeds the ECU is a switch. I'm told it's near the distributor.

thanks for any help!

I believe I'm looking for this guy: https://images-na.ssl-images-amazon....SR228,320_.jpg

There is one on the port side of the block below cylinder 7 spark plug

Thanks, I think that's the sender for the gauge. That's the one I pulled as a test (alarm still going off), no effect.
I think now I'm looking for the switch one. I'm told it's near the distributor, but I'm stuck at work, and the boat's at home...

I could be wrong about this , its been a while. But does it look like this? If so I think it has 2 wires that go to it. To bypass it unplugging it would do nothing. You would have to Jump the 2 wires.
. And it is on the port towards the back of engine close to #7

Chris

so you are following my advice ? The dollar blinky tool really does nothing I wanted to let you know in your other thread and have no idea where you found those fault codes in the link below ?

https://www.offshoreonly.com/forums/...en-engine.html

You need to post your engine serial number to help with the correct set up and correct parts. The year of the hull means nothing. Merc has service Bulletins on the MEFI 3 350 especially the HO mag that might also be the issue.

Yes, you correctly determined that it could be the oil pressure switch.
However, I won't know for sure until I disconnect it tonight and start the engine.
The gauge shows correct oil pressure, so I don't believe it to actually be low.

In my previous troubleshooting, I was unaware that two oil sensor devices existed.
I did test (what I thought was) the oil pressure switch.
Turns out I most likely disconnected the sensor for the gauge, which would not impact the alarm.


The LED light test identified 2 DTCs, for which I replaced the sensors.
Cost of the tool was $0.00 as I had a 12v LED laying around.
I plan to test the port engine tonight to review any open DTCs.

Here is a relevant bulletin:
http://www.boatfix.com/merc/bullet/99/99_03.pdf

Here are the codes:
https://www.offshoreonly.com/forums/...mefi-codes.jpg

CodeMate User Guide (With codes)
http://www.rinda.com/acro/codemate.pdf

More MEFI info:
Pirate4x4.Com - The largest off roading and 4x4 website in the world.

Here are the STRB engine blink codes I received.
https://www.youtube.com/watch?v=XdLRhrTanxI&feature=youtu.be
14 & 23
Both sensors were replaced, codes cleared. Currently no codes show.

Tonight I will test by disconnecting the correct oil pressure switch.

STRB Serial: 0M047350

Thanks!

Man, do I hope it's just this $25 switch. Previous owner cut alarm wires on each engine. Vs. fixing it...
They also pretty much beat the rest of the boat as well. I've spent all winter making this thing whole, and could only test the engines since last week.

I do appreciate the help and offer, but I'm in PA... so that would be quite the haul.
I really did think I tried the oil pressure switch. I never realized the engine had two for oil and water. Cars (mostly) just have one sensor each, and the computer sends the data to the dash.
Why bother with two sensors? That's just more cost...

. Scan tool can guide one to fix it correctly currently and down the road. Inwhich down the road one will need if not currently. Like I said winky blinky is worthless for anything that requires more depth diagnostics rather changing sensors out - inwhich can lead to wasting time and money plus no water time sitting idle not fixed correctly.

You need to see parameters from the scan - key on and running, example the IAT temp while key on plus running, also voltage readings and that includes the 5 V reference readings as well from the scan tool. This really is why the winky blinky is not recommended.

Understood. I'm aware of the value of the Scan Tool, and will most likely one day purchase one. I do IT work for a living, and am a data nerd. If I'm unable to locate the source of the alarm, it will be in the near future. Here in PA, I still have another 2-4 weeks until the start of boating season. I'd like to get it fixed, but it's.. on a trailer and currently 50 and raining here. Not ideal boat time.

I have a mobile marine mechanic I've called as well, who has a scan tool.
However his rate is obviously more than $40 in sensors.

I made the mistake of testing against the wrong oil pressure device. I admit it. I'm human.
I didn't know the engine used two.
(Which I still think is stupid as it only adds cost and complexity, while not adding redundancy).
My full time job isn't marine engine repair. I do this for fun, save money, and I like learning.

If the scan tool was realistically priced, say $100 or even $200, I'd have one by now.
The barrier to entry is intentional, I get it, it's free market. If they can get it, good for them.

It would be great to see a scan-tool rental system, but I get that no one wants to risk loosing their investment.

I changed my post # 8 to maybe a better answer and I was throwing the other issues out in the mix for possible the wiring side that can effect sensor issues on top of -- I posted ( POSSIBLE ) open and short for 14 and 23 --- but now deleted it cause of the confusion on my part not being clear without writing a long post to explain that side of it. . . That was my mistake for the lack of info

Engine serial number helps with system set up and parts plus the location of installs. I understand what you are saying about asking where is the location for the switch ? Engine serial number will help with the exact location

No apology needed, I didn't dismiss the pressure switch issue, I just thought I actually HAD tested it.
Which is why I moved on to DTCs as a possible cause of the alarm.

Like I said, I appreciate any help, this boat was so beat you'd think they did it on purpose. I didn't know nearly enough when I bought it... and some days regret buying it!

Off Topic:
Things I've had to fix because the previous owner was brain dead.
Engine Alarms
Shifters
Trim Tab wiring
Trim Tab Motor
Radio (was none)
anchor locker
Bilge Pumps
Blower motors (neither worked!)
bow light (didn't work)
distributor cap, plugs, wires
trim rams on BOTH drives
flame arrestors soaked with oil
glove box broken
Horn button AND noise maker broken
stern light base broken
trailer brake pads gone
trailer tires shot - 2 wouldn't hold air

So.. yea... feeling a little ripped off and stupid here. Next time before spending $ on a boat, I get a full inspection!

I also had to do the JR Marine transom fix to both over the winter.

Hey BUP his serial number may be in the range of the fuel pressure sensor area, don't know for sure but figured you would. That said he won't know without a scan tool and seeing if he has

MCM 5.7L EFI: With D7ED or D798 checksum.

STS, the oil sender is below the distributor on the rear deck of the block, port side

Thanks, I will come back and check out if you can post engine serial number. I will admit my post was not clear at all and pointed in one direction only inwhich was my fault totally. The only thing I was clear on was the word possible.

Its
STRB Serial: 0M047350

fuel pressure sensor and IAT was in 1999 model year and fuel pressure too low cause a solid horn / beep for 5 seconds then goes off and of course had it serial number break as to exactly when.

there is a service bulletin all about it as well.

Found the oil pressure switch, thanks. That was the issue. Soon as I saw it had oil on top of it, I knew that was most likely the issue. Disconnected the wire, tested it engine off/on, and yep that's it. New one ordered.

So, of course a 16 yr old kid takes out my mailbox last night... have to call the post office and make sure I can get this part I need by this weekend!

Yes I could just run the old one, with the wire disconnected, but I already pulled the thing out.
Who could have anticipated my mailbox getting run over?!

Thanks everyone, alarm is quiet, and I fixed both DTCs I had, should be a good summer now!

Bummer on the mail box, folks around here will sit it on top a trash can or drum while fixing it.

They have the same switch at the local auto parts store, there not marine unique

POST # 3 ------- and keep in mind I never seen the switch --------------- https://www.offshoreonly.com/forums/...en-engine.html.

Man sometimes you guess right and sometimes you get lucky and SOMETIMES your just plain old good at what you do. Pick one.