Oil pressure sensor 350 MAG Mercruiser Smart Craft

[spunkyman]

I started a new thread because my other one had several topics and this is the last of my problems !! (I think)
Previously, I'd been getting a reading of FULL (100PSI) on my gauge for oil pressure when I turn the key. When I fired up the engine and gave 2000 RPM in neutral on the hose, the PSI would come down to 50 PSI.

The gauge is NEW and the sensor is NEW. I measured the harness plug. I get 4.78V on blue/black and 5v on grey, but I get nothing on black/pink. When I start the boat, the voltage goes from 4.78v on blue black to 4.82v. Still nothing on black/pink. Am I getting power where I should? When I remove the plug to oil sensor, gauge goes down to 50 psi with key turned. So.... no power to black/ pink.... any ideas on how I can get this sorted? Also, could this be why at 4000 RPM out on the water, my engine is limiting power? it's telling me that something is up with the oil pressure and goes semi-protecting mode?

thx so much to all you wonderful, smart guys out there .. you've saved me !

 

[QBhoy]

Is this a digital reading on smart craft or a analogue gauge ?

 

[spunkyman]

It is reading on the smart craft 4 in 1 gauge, but I suppose that's an analog gauge as it has needles..... see picture. I've tried an identical gauge to see if it's the gauge, and the same reading shows on a NEW 4 in 1 gauge. The oil sender is also new. Is there suppose to be 5v to ALL 3 conductors? maybe a resistance thing... not sure.

 

[GA_Boater]

What is the part number of the 4 in 1?

 

[spunkyman]

here's the back

 

[QBhoy]

Do you know anyone with a vessel view mobile that you could borrow or even a scan tool ? The vessel view will tell you pin point accurate and every reading from the engine. Literally every readout and at least twice the readings of the dash board.

 

[spunkyman]

I do not. I guess it's of to the marina. The other fix might be to try and rule out the plug by checking for 5v on pink/black behind the plug. I have an identical extra plug with wires on it from a mother harness and could splice, however, I fear that its a break or issue somewhere in the wiring. Here's a question. Is there any other way I can get the 5V to the plug from any other place? Or does it HAVE to come from that specific wire that currently isn't reading 5V (if its oil pressure specific going to the gauge)?

 

[spunkyman]

UPDATE.... My "new" sensor was JUNK. I simply switched out the oil pressure sensor for another NEW one and my PSI went to 0 when the key was turned - something I never got with the other "NEW" sensor I'd been dealing with (It showed 100 PSI) SO... if any of you get a high oil pressure reading when simply turning the key - it means you have no reference and your sensor is JUNK !

 

[QBhoy]

Excellent news. Did your engine come out of its guardian mode ?

 

[spunkyman]

Hi ! Well, I took her down to the 1000 islands Saturday and she ran great up to 3500 rpm and then started backfiring and wouldn’t get any more power/speed after that. I’m not sure if that’s guardian mode or something else is going on .... I put 3/4 of a tank in to mix with the old fuel but that didn’t fix it. Any suggestions ? I don’t see an inline fuel filter .... could there be some kind of filter somewhere else ? Is there anything in the fuel pump “box” ? It runs so nice up to that point ! I’m almost there !!

 

[alldodge]

You shouldn't have an inline filter, only the canister type. Back firing is from a lean condition and normally the ECM will retard timing if things like this starts to happen. Have you tested fuel pressure ?

 

[spunkyman]

I have not ... not sure how to do that ... I put in a new fuel pump and cold fuel pump too ... but, we know that parts could be faulty !

 

[alldodge]

Ahh serial numbers are always best but your an MPI
With that attach it to the fuel rail at item 18

https://www.mercruiserparts.com/bam/subassembly/31747/7585/90

 

[spunkyman]

can I use the same gauge I use for compression tests?

 

[alldodge]

Maybe and yes, sort of
To get correct pressure you need the air out of the line that feeds the gauge. With a gas pressure gauge it has a clear bleed tube so the air /gas mix can be expelled into a container.

If you use the compression gauge, your looking for pressures in the 43 psi area. The gauge needs to connect to the Shrader valve on the rail, so need to adapt to the fitting.

It would be easier if you can get a loaner tool at the autoparts store, or buy the correct one. They also sell ones in kits with several fittings for different system for not much more

https://www.amazon.com/OTC-5630-Fue...ocphy=9057911&hvtargid=pla-403890609833&psc=1

 

[spunkyman]

ok.. i suppose I have to measure the fuel pressure at 3500 RPM when it starts backfiring? ( as it runs fine up to that point)

 

[alldodge]

Check it from idle up to that point to see if pressure changes

Your saying backfire, and if it actually is then ok, but if it is the engine starts missing then it could be something else as in gear switch, low battery voltage

 

[spunkyman]

ok.. checking on that tool tomorrow !

 

[spunkyman]

Could be a miss .... it’s a bang ! The exhaust is fairly dirty ... black residue ... while on the hose.

 

[alldodge]

3500 rpm on a hose will burn the impeller

Since its a bang then must be backfire, need to get pressure check in the water