Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

[wpowell323]

The oil pressure sensor that is in the boat is reading 35 lbs when the motor is cold. The gauge on the dash reads 70+. When you cut the motor off This sensor will go to zero, but for some reason when you crank the motor will not read pressure on high end. I put an external gauge and it reads 70+. The problem is when the motor is warm and the oil thins out a little this sensor will sometimes read under 20 lbs. which sends the motor in full guardian mode. When this happens the gauge on the dash is still at 40+ pounds as is the external gauge. So i can only assume the sensor is bad.

So I ordered a new sensor and replaced the faulty sensor with a new one from mercury. The alarm sounded 2 beeps a minute as soon as i installed it so i put the DDT on the motor. the oil pressure reads 50.7 pounds which indicates a faulty sensor. I returned the sensor and got another. When i installed this sensor I did it with the DDT hooked up. Before I ever cranked the motor I noticed the DDT showed like 29.2 pounds of oil pressure with the motor off which is an indication the sensor is bad, when i cranked the motor it went to 75 lbs and then within a few seconds went to 50.7 and i got 2 beeps. Again showing another bad sensor. I cut the motor off and the ddt still showed pressure at the sensor, I cranked it back up and it went to 50.7 with 2 beeps.

The wiring harness on this boat is brand new. There are no breaks or corrossion. the plug at the connector is fine as far asi can tell, the pin at the ECU also appears to be fine. So did I just get unlucky and get 2 bad sensors, or am i missing something? I am going to take this one back tomorrow and luckily my friend owns the place, so he is going to call Mercury and speak with a tech for me, but I know there are some very knowledgeable people on here so I am looking for some input from someone who might have experienced something similar.

 

[Bondo]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

or am i missing something?

Ayuh,... A Bad Ground would be My WAGuess...

 

[Fun Times]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

You might be dealing with a sensor that is not getting a good ground, If there is any paint in the threaded area of where you install the sensor then you will get this problem and the sensor will give you all kinds of different readings. For a quick test you could try touching the threaded sensor part with a good sepret ground wire and watch the scan tool to see if the reading changes at all. If any paint clean the area up. Check all the power & ground wires to the batterie cabels and to the engine itself for clean [no paint ect] and 100% tight. Also there have been some reports of static electricity killing the sensors, So you might need to ohms check the sensor it self. I went back and found a good link here on I boats about some one going thru almost the same thing you are going thru but in a different area,. I am not saying this is it but some thing to keep in mind is all. Good luck with it.http://forums.iboats.com/showthread.php?t=325435&highlight=static.

 

[wpowell323]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

I spoke to a friend yesterday and he said it sounded like a ground issue to him. I know all the grounds are tight and clean, as I checked those. Everything on the boat and motor works perfect except this stupid sensor and the trim sensor on the outdrive, so it seems like if it was a ground issue i would be having other problems, but maybe not.

Could i run a ground straight from the battery and touch the sensor? or since this is a 3 wire sensor wouldn't it have a ground coming to it through the harness? If so I guess I could trace that ground and see where it goes or splice into it and make a new ground. Also seems like if it is screwed tight in the block then it would have to be grounded, but i know when you are dealing with issues like this sometimes things are screwy. The sensor appears to be brass, so maybe that won't allow it to ground to the block and if so I guess touching it with a wire wouldn't matter? Also any idea why one sensor would have a faulty reading, but at least seem to increase and decrese properly, meanwhile 2 other sensors that are plugged into the same harness test bad. Seems like if it were a ground issue the problem would be the same regardless of the sensor.

I wish i could just disable the guardian. As long as my gauge says the oil pressure is good, I don't need the computer telling me something different.

 

[Fun Times]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

I am just guessing about touching the sensor with a ground to see if any thing changes, But i do not see anything wrong in trying it out just to see.I have not tryd it my self yet. You might even have a problem in side the PCM itself giving a wrong reading.Yes the best idea would be going from the batt over to the sensor if you want to try it, It's up to you if you want to or not. Did you read every thing in the other link? It worked for him and that was coming from mercruiser, I my self thought of trying to touch the sensor might work in this case after reading this link, But I could be wrong. http://forums.iboats.com/showthread.php?t=325435&highlight=static

 

[wpowell323]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

Well Mercruiser said to their knowledge there is no problem with the sensors. I told him i had read on the internet to ground the sensor and he said that sounded like it should help? seems like he isn't much help..

 

[wpowell323]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

Went to the lake today. I grounded the sensor that was in the boat. Actually I first checked to see if it was grounded by hooking a wire to it and the touching the wire with a test light. It was grounded. I then grounded it anyway and the sensor still had a faulty reading. Then i installed the "new" sensor. I checked to see if it was grounded and it was. I then grounded it anyway. With the motor off that sensor reads 29.9 pounds. When you crank the motor is goes to 94.9. After a little run time it went to 50.7 which is the preset range for a faulty sensor. I guess i am going to get a third sensor, unless someone here knows how to check the sensor not in the boat. Or can suggest something else to try. I guess it is not impossible that I got 2 bad sensors in a row.

 

[wpowell323]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

Just got off the phone with Mercruiser again. Seems that their computer has a improper part number. They sent me a power steering pressure switch, which is a 3 wire switch that evidentally looks identical, but must read different. the part numbers were the same except for the last digit. I have a feeling this may fix the problem.

 

[Fun Times]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

Just got off the phone with Mercruiser again. Seems that their computer has a improper part number. They sent me a power steering pressure switch, which is a 3 wire switch that evidentally looks identical, but must read different. the part numbers were the same except for the last digit. I have a feeling this may fix the problem.

It sounds like it should, And if it don't then you will need to ohms check the wires from the sensor to the PCM, to see if it has any kind of short/open And check them for good power and ground from the sensor to the PCM, [Any where from .5 volts up to 5.0 volts Is the range.] And if the wires are ok then you have a bad PCM. Good luck with it.

 

[wpowell323]

Re: Problem with oil pressure sensor on 2007 Mercruiser 350 MPI

Amazing how things work when they actually send you the right part. Thanks for the input and suggestions