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oil pressure sending unit

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mstrcrftr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Topic: oil pressure sending unit
    Posted: Oct/07/2017 at 8:44am
something funky is going on with my oil pressure gauge.  this is a new install on a new engine.  i have a tee fitting on the block for the sending unit.  one side of it goes to a mechanical gauge on the engine and that works fine.  the other side goes to an electrical sending unit for the dash gauge and its not working.  when i jump the sending unit wire to ground, the gauge works.  i tried replacing the sending unit and it still does not work.  any suggestions on what to do?

thanks
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 6768rogues Quote  Post ReplyReply Direct Link To This Post Posted: Oct/07/2017 at 9:36am
Did you use some type of thread sealant or teflon tape on the threads of the sending unit or Tee? If so, it might electrically isolate the sending unit from the block. That won't matter for the mechanical gauge. Otherwise, I would guess that both sending units are bad or wrong for the gauge.
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mstrcrftr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/07/2017 at 10:33am
i thought of that and tried grounding the case of the sending unit to the block, no change.  do you think its possible that i have two new bad units?  both were ordered for 80 psi gauge.  i was wondering if the unit was different for an 80 psi, but you would think that the gauge would at least move if it was for a 40 psi gauge.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Airdrie AMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/07/2017 at 10:54am
Do you have a good ground strap from the engine to chassis?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rockAMX Quote  Post ReplyReply Direct Link To This Post Posted: Oct/07/2017 at 1:15pm
By the dash gauge, do you mean the oil light or a gauge?
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mstrcrftr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2017 at 9:53am
battery cable goes directly to the block and yes the dash has an actual 80 psi gauge.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rocklandrambler Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2017 at 11:27am
Could it be the mechanical pressure line is siphoning off enough pressure that the electrical sending unit can't sense any pressure?  Does the electrical gauge work OK when hooked up by itself?
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mstrcrftr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/08/2017 at 7:28pm
mechanical gauge reads 60 at idle.  not a pressure bleed thing.. its gotta be two bad sending units.  everything else works..
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mstrcrftr View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote mstrcrftr Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2017 at 1:12pm
still having issues with this.  can someone look at the drawing below and confirm that this is how the circuit actually works?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote 304-dude Quote  Post ReplyReply Direct Link To This Post Posted: Oct/11/2017 at 1:23pm
It is possible that the instrument panel circuit is damaged.

You can test with the engine running, by ohming the output on the switch directly. You may need someone to increase the engine RPM to show resistance change from idle to 2500 RPM.

If you see the resistance change, it is possible the one of contacts where the oil pressure gauge has a broken trace or wire.
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