[P@blo]

My oil pressure gauge stops working and tried to ground it out at the sending unit off the block and nothing. If I put 12V too the wire going to the sending unit it will peg out to the right and then will work for about 3 hours and will do the same thing. It will stop working and I pull the sending unit wire and put a 12V source to it it will work again for a little wile. Would this sound like a bad ground at the dash to the gauge or is the actual guage ?

I don't have very much electrical background so any help would be great.

Thanks

[george kujanski]

The sender used with the gauge presents a range of resistance over the range of pressure, i.e. when pressure is zero, the sender has a certain resistance, and it changes as the pressure goes up.

grounding the wire at the engine or applying 12 vols to it is NOT the thing to do.....it may swing the gauge from one extreme to the other and damage it in the process.

The proper thing to do is to attach a resistor equal to the zero psi resistance from the wire to ground to check the gauge reading. Likewise, attach the max PSI equivalent resistance to it to see if the gauge reads properly at the other extreme.

There was a recent post in this forum which stated the actual resistance values to use. I'll see if I can find it.

The OEM senders are not very accurate, and after all these years may very well be defective.

Here's the link: http://forums.maxperformanceinc.com/...d.php?t=479094

Apparently it may be ok to ground the sender wire as zero ohms corresponds to one end of the scale.

George

[79firebird_99TA]

Sounds like the gauge to me or the 12V to the gauge. The gauge is really nothing more than am ammeter that is measuring current. As the resistance of the sending unit varies (which is directly propotional to the oil pressure) so does the current. That said, you have 12V connected to one side of the gauge and the other side running to your sending unit. The fact that you didn't even get any deflection when grounding the lead at the sending unit would be one of three things: open circuit due to bad gauge, open wire or no 12V to the gauge.

Pull the gauge and put a 1.5V battery across the leads and see if it slowly deflects as it should. Also check for 12V feed to the gauge, and then finally continuity to the sending unit.

[P@blo]

Awsome!!

Will let you know how it works out later today.


Thanks

[P@blo]

Sorry for the delay on this one. To update: 12V to the harmonica plug was confirmed first. Then I pulled the gauge cluster and checked all the circuits on the board. I had found the 12V connection to the 31 terminal had considerable resistance from the gauge to the plug so I backed out the terminal nut and tightened it back down. Seems that took care of the issue and should have known because the gauge would not zero on preignition.

While I was at it I verified the gauge itself was working by taking a AA battery and watching the needle deflect. And I replaced all the bulbs in the dash with new LL versions. Less lime I spend contorted the better.

Thanks again for the suggestions!

[indymanjoe]

better late than never LOL