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Unread 02-01-2009, 12:50 PM   #1
chet44
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Bench testing a electrical oil pressure gauge

The subject title speaks for itself. How do I go about testing this? I installed a new gauge, and sending unit, and I've got nothing. The gauge is getting power, and I checked from the sending unit on the engine to the sending unit terminal on the gauge with a continuity tester, which is good. Is there something I'm doing wrong here?

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Unread 02-01-2009, 01:32 PM   #2
Coiz
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John Strenk has good links in his signature. If you pull the wire off at the sending unit and momentarily touch it to ground, does the gauge move? If so, that confirms the gauge and sending circuit are fine. Did you use some sort sealant between the sender and where it screws into the block? The case of the sending unit needs to be grounded. If you went crazy with the thread sealer/tape, that may be your problem.
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Unread 02-01-2009, 01:55 PM   #3
chet44
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Well, I went out and did like you said. I took the wire off the sending unit and pressed it against a exhaust manifold bolt and the gauge pegged. I then took my continuity tester and attached one wire to the negative battery terminal, and the other to the housing of the sending unit, and I got good tone. That means the ground on the sending unit is good, right? So I hope that means the sending unit is bad. Also, on this same note, I also installed a new speedo cluster. Everything works on that except the temp gauge. I also took the sending unit wire off and touched it to ground, and the gauge moved, slowly. Both sending units are new, both gauges are new, the wiring harness is inherited, but looks brand new. I'm thinking my next step is to run separate wires from the sending units right to the gauges and see what happens.
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Unread 02-01-2009, 02:40 PM   #4
chet44
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Okay, I went to John's links, followed the instructions (To the point I could, anyway). I need a 12 volt test light, and DIGITAL multimeter. I have a $9 K-Mart special that has a really confusing scale on it. I also think John is right, and I have bad ground(s) somewhere. A test light will check that better than a meter. So, I'm off shopping, again, I'll keep you posted.
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Unread 02-01-2009, 11:26 PM   #5
rodjr
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im having similar prob, mine reads 20lb all the time no matter what. looked at johns gauge facts now im more confused. i have a 1" deep gauge and when i test w/ 22.5 ohm resistor it reads 30lb or so by his chart that would be about right for 2" deep early gauge? my grounds are good gauge tests ok sending unit reads 128 ohms eng off, but with engine on my meter bounces o.l. no idea whats goin on but if i solve ill let you know.
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Unread 02-02-2009, 06:29 AM   #6
John Strenk
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Quote:
Originally Posted by rodjr View Post
im having similar prob, mine reads 20lb all the time no matter what. looked at johns gauge facts now im more confused. i have a 1" deep gauge and when i test w/ 22.5 ohm resistor it reads 30lb or so by his chart that would be about right for 2" deep early gauge? my grounds are good gauge tests ok sending unit reads 128 ohms eng off, but with engine on my meter bounces o.l. no idea whats goin on but if i solve ill let you know.
Are you talking your ohm meter reads O.L. or your oil pressure gauge?

As far as testing the sending unit. I just chuck it into a air chuck and vary the pressure on the air compressir to check out the sending unit.



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Unread 02-02-2009, 08:34 PM   #7
rodjr
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ohm meter. w/key off it reads 128 to 132, key on ohm meter goes nuts, o.l., flashing 0000 multiple numbers to fast to read, o.l. all over. oil gauge reads 0 press key off, 0 press key on, 20lb engine running always never changes even a little. can not get ohm reading w/ key on engine running or not. gauge body good ground 0 ohms sender 0 ohms. should 1" deep gauge read 30lb ish w/ 22.5 ohms? johns gauge facts suggest not.

Last edited by rodjr; 02-02-2009 at 10:42 PM..
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Unread 02-02-2009, 10:23 PM   #8
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JOHN, YOU ROCK!
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Unread 02-03-2009, 03:06 AM   #9
John Strenk
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Quote:
Originally Posted by rodjr View Post
ohm meter. w/key off it reads 128 to 132,
key on ohm meter goes nuts, o.l., flashing 0000 multiple numbers to fast to read, o.l. all over.
Don't even try, ohm meters don't work on a hot circuit.
Is this reading with the oil gauge still connected to the oil pressure sending unit?

oil gauge reads 0 press key off, 0 press key on,
20lb engine running always never changes even a little.
can not get ohm reading w/ key on engine running or not.
Don't even try, ohm meters don't work on a hot circuit. You could use volts if you know how to interpit the readings.

gauge body good ground 0 ohms sender 0 ohms.
should 1" deep gauge read 30lb ish w/ 22.5 ohms?
johns gauge facts suggest not.
My experiance shows it's not. A 22 ohm resistor should show full scale on the meter.
Two gauges, both not working on the engine still suggest a ground problem. test for continunit between the engine and dash. You might have to disconnect the wire on both gauges to test this as they might preform thier own ground path if left connected. Together they can be interfering with each other.
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