5.0 PEFS Oil gauge headaches?!?!

[TrentD]

It all started when we pulled out of a cove and the starboard engine oil pressure fell flat on its face. It sent me into full panic dropping that engine and checking the oil level that looked fine. Returned back to the helm and restarted with the needle on 0 trying to get home I gave it fuel and with the increased rpm I could get it almost back to 40.....fast forward

I took the starboard sending unit and swapped with the port engine....it was back at 40 all was well....the bad part was the other engine was at 40 too?!? Damnit!

The next day port engine was back at 0-20psi, so I bought a mechanical gauge. It was reading between 45 and 48psi... bouncy at idle (I assume is normal)

I replaced that sender....no change on the dash.

Ah....HAH! I said, I'll swap the port and starboard gauges on the dash that will reveal the gremlins....NO CHANGE!!!

Sending units are homing out within specs, I have 8.5 volts coming to the sending unit. Today I'm going to place a 100 ohm resistor online to ground with the sending wire to see if gauge will come to 40 if it does not I will run a wire directly off the gauge to the resistor and see if that changes it. At this point it's all coming back to the wire between the gauge and the sender, that's all that's really left. I may also undo both sending units and run a jumper from the wires to opposite engine gauges as well. So after writing all this...anyone have a schematic for the 5.0gi.....to the gauges, I found the engine schematic but the oil sensor terminates into the big harness and that's as far as it goes.

2001 FW 285 Sundowner W/ twin 5.0 PEFS 97 hours on each

 

[Scott Danforth]

clean your contacts and connections under the dash, and at the motor. my guess is you have a break in the wire, or a bad connection. any corrosion will lower your gauge reading. also, if your voltage to the gauges is less than 12 volts, your gauge values will drop.

dont cobble something up with resistors..... thats just not right

your sender should be a 240-33 ohm sender and so should your gauge (your fuel gauge is also a 240-33 ohm gauge and most likely so is your water temp gauge)

to test, you should read 240 ohms between signal and ground at 0 psi, and 33 ohms at what ever PSI your gauge reads at the top end of the scale (80, 100, 150, etc)

to test your gauge, you can use your resistor between the signal and ground. since the gauges are somewhat linear, you should be about 75% of full scale at 100%

 

[Bondo]

Ayuh,..... Clean the Ground Cable ends,... Both on the battery, 'n on the motor block,.....

 

[TrentD]

I'll take that into consideration. I'll run a ground from the sending unit body directly to the battery to test your theory. I don't want to boast but this boat has spent 14.5 years of its 16year old life in Arizona...corrosion does not appear to be a problem. I'll still test your theory though by running a direct ground.

 

[TrentD]

clean your contacts and connections under the dash, and at the motor. my guess is you have a break in the wire, or a bad connection. any corrosion will lower your gauge reading. also, if your voltage to the gauges is less than 12 volts, your gauge values will drop.

dont cobble something up with resistors..... thats just not right

I just told you I was going to test with resistors then you said not to...then you end with telling me to?



your sender should be a 240-33 ohm sender and so should your gauge (your fuel gauge is also a 240-33 ohm gauge and most likely so is your water temp gauge)

to test, you should read 240 ohms between signal and ground at 0 psi, and 33 ohms at what ever PSI your
gauge reads at the top end of the scale (80, 100, 150, etc)

to test your gauge, you can use your resistor between the signal and ground. since the gauges are somewhat linear, you should be about 75% of full scale at 100%

I'm not sure on your theory about 12 volts...the benefits of having twin engines is one acts as a control for testing and that engine also gets 8.5v to the sending unit and operates normally

1. If I can put a resistor to ground and it works then the sending unit is the problem
2. If it doesn't then I will wire directly off the back of gauge with same test, if it doesn't work then the gauge is the problem
3. If it does work with a direct wire off gauge then I have a problem somewhere in the factory wiring

Simple as that

 

[Scott Danforth]

in short, if your connections are not shiny enough for your kids to eat off of, then they are not clean

 

[TrentD]

in short, if your connections are not shiny enough for your kids to eat off of, then they are not clean

Mine are clean although I disagree they don't have to be polished to be operational. That's nonsense I work with low and high voltage on the regular and that's horrible advice. Just say that the connections need to be checked and pretty clean. If I'm getting the same volts and ohms at either end of the chain the connection is not the problem. I'll have to verify the sending units ground this afternoon, I'm fairly convinced I have a problem in the harness somewhere I'll update when I get more data tonight

 

[TrentD]

So in the wiring harness on the back of the engine there is a big round molex style plug with 7 or more pins in it. With the help of my cell phone on the dash recording gauge movements and a 75ohm resistor (gives 3/4 pressure reading with out engine running) allowed me to crawl all over the harness wiggling and talking. Re watched the video and when I started playing with that plug the gauge looked like the exorcist. Went back pulled it apart looked at it it was clean so I sprayed it with some contact cleaner replaced tested several ohm values through the gauge range and all is well. Re assembled the wire to the sender and it reads correctly now ....case closed

 

[QBhoy]

If you are getting 8v, you aren't testing across the +ve and ground. Likely you are testing across the signal and ground with a bad sender or broken wire?
If it is indeed only 8v...you have a bad earth or corroded connection along those lines...as suggested.

 

[QBhoy]

If you do get 12v...do the standard 0-max gauge test...if all ok, then look towards the sender unit and it's wiring.

 

[QBhoy]

Hi

There are a few loose wires on these engines normally. Did you get the mixture adjustment cover off ?