Oil Pressure Sending Unit Conversion

[A robs 23]

It appears so haha


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[A robs 23]

My oil pressure gauge appears to read “H”, which is in the “60” position of the alternative gauge, with numbers.

When I increase RPM above idle, the needle goes slightly beyond “H”.

The oil pressure gauge is brand new. The sending unit is used, off an old 350.

When I turn the key off, the needle stays pinned. Once I recycle the key to 12V on, just prior to ignition, the gauge drops back down to zero.

Should I add an inline resistor to fine tune my gauge needle position?


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[bd]

Three diagnostic steps to take:

• Use a mechanical test gauge to measure the engine oil pressure and acquire an actual number.
  
  
• Use whatever means necessary to inspect the 9/16" hex base nut of the sender for a two-digit number.  This is the sender calibration in PSI.  It should be 60.
  
  
• Procure a 30-Ohm, 1/2-watt resistor (or substitute a ~1,000 Ohm potentiometer, adjusted to 30 Ohms using your multimeter).  Disconnect the sender wire from the sender.  Insert the resistor between the sender wire and a shiny clean ground point.  Switch the ignition ON and read the OP gauge.  It should sweep to center scale.  Does it?

The gauge needle hanging at any given position with the ignition OFF is irrelevant since there is no spring to return the needle to zero.

[A robs 23]

I have ordered a resistor and it is set to arrive on Thursday of next week.

I ran my truck to warm up the oil and see if the gauge would come down at all. It did not.

During the engine warm up, I have discovered my temp gauge also does not work.

Leading from my coolant temperate sending unit plug, I have a dark green wire running to my firewall - it runs to location 931 on the bulkhead(male). Instead of the crkt 35 position as it should, based on the wiring diagram provided.

Inside my cab, I have my dark green wire on my pinout @ position #9. I have traced this to the the appropriate crkt 35 position on the bulkhead(female).

It appears that crkt 35 has been switched at some point, on the bulkhead(male) in the engine bay.

I went to switch the terminal again, inside the cab, and simply place the dark green wire in the crkt 931 position to provide continuity from the plug, to position #9 on the pinout. I discovered that there are TWO dark green wires running to that terminal.

Will this cause any issues, If I move this terminal, to match the bulkhead feeder wire under the hood? I am not sure why there are TWO dark green wires.


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[bd]

I have a dark green wire running to my firewall crkt 35 - it runs to location 931 on the bulkhead(male).

^^^^ This comment is unintelligible.

Inside my cab, I have my dark green wire on my pinout @ position #9. I have traced this to the appropriate crkt 35 position on the bulkhead(female).

I went to switch the terminal again, inside the cab, and simply place the dark green wire in the crkt 931 position to provide continuity from the plug, to position #9 on the pinout.

Why not route the wires through the bulkhead so they match the factory diagram?  It will make the current project, not to mention future diagnoses, so much easier. 

It appears that crkt 35 has been switched at some point, on the bulkhead(male) in the engine bay.

I discovered that there are TWO dark green wires running to that terminal.

I think it is likely that age, heat and chemicals have altered the "apparent" colors of the original wiring.  Ckt 931 from the factory was dark blue.  Still, anything is possible.  Trace the wires conclusively and match them as necessary.

[A robs 23]

I updated my post, to hopefully make more sense.

Why would there be TWO dark green wires on the female side of the bulkhead, crkt 35?  Did crkt931 have two dark blue wires?

I was hoping to not have to repin the male side of the bulkhead, as it has the anti corrosive compound.


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[bd]

Why would there be TWO dark green wires on the female side of the bulkhead, crkt 35?

I misinterpreted your prior question.  The wiring diagram is your friend.  Look at it.  Study it.  On vehicles having idiot lights instead of gauges (the "BASE" configuration such as your truck before the conversion), the second green wire runs to the ignition switch where it grounds through the switch in the crank position.  This supplemental circuit illuminates the red overtemp warning lamp during engine crank for a "warning lamp test."  The supplemental wire is unnecessary when gauges are used.  Hence, it can be severed at the bulkhead connector and/or removed from the ignition switch connector and taped up when converting to gauges.

[A robs 23]

Ok that makes sense! Thank you.

I am still very ignorant with the diagram. But I have learned quite a bit since you guys have started to help me utilize them. I saw the “base” one the diagram but was unsure what it meant.

Now I know.

Thanks again.

Will report back when I have made more progress now.


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[bd]

Understandable.  The "base" note as printed on the diagram is more of an anomaly, meaning that it is not in common usage.  It is encountered only occasionally.  If you have specific questions about how to read a diagram, don't be bashful about asking.

[A robs 23]

I procured a 30ohm 1/2watt resistor.

With the resistor,the needle sweeps back down to half.

Should I now wire this inline permanently?


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[bd]

The resistor just verified proper gauge function.  It is for test purposes only.  Do not install it permanently!  Sounds like you have a faulty oil pressure sensor.

[JohnnyPopper]

Aw come on bd, let him leave it permanent before we get to five pages!!!

[bd]

Is it straining your attention span?   

[JohnnyPopper]

Touche my friend, touche!!

[A robs 23]

I ended up putting the double green crkt35(under dash), in the 931(under hood)position to provide continuity from coolant temp sensor to pinout. I left the second green wire, connected from the bulkhead that illuminates the test light.

I replaced my oil pressure sending unit with a slightly larger, 60psi calibrated sending unit.

Voltmeter, oil pressure and coolant temp gauges all work properly now!!

I now have to troubleshoot my fuel gauge, but will do so in a different post if required. I see there is a lot of info on this, so I will do my best to work through old posts first.

When my new tach [faulty from factory]comes in, I will post a final picture.

Thanks for everyones time!


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