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  #1  
Old 08-11-2015, 09:59 PM
Yadkin Yadkin is offline
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Default Oil pressure sender issues

After finding out my off-the-shelf oil pressure sender is not accurate I did some research and found this site:

http://www.classictiger.com/mustang/...ssureGauge.htm

Then bought an Autometer 2242 and installed it. The unit is tall so I used a brass 45 and an adapter to plumb it. I used the correct sealant (not teflon tape or plumbers teflon) and get 0 Ohms between the sensor tightening nut and chassis ground.

I have a good engine ground.

My gauge will not work with this sensor. When the engine is running it barely moves if at all. I tested it by grounding the sensor connection and the gauge slowly moves past H as expected.

The resistance between the sensor post and chassis ground is 254 ohms (corresponding to 0psi) with the engine off and the gauge disconnected. Repeatable. At warm idle it measures about 130 ohms (35psi) and at higher engine speed about 95 ohms (55psi).

These values change when I turn the running lights on. Ohms decrease to about 148 with the engine off. Repeatable. Again, the sensor isn't electrically connected to anything other than the engine, and my ohmmeter.

If the engine is running and gets hot enough to turn the electric fan on, the resistance goes up in the mega-ohm range.

I have no clue what is happening. As you may know, I have done extensive electrical modifications to this car, but everything is working (except the fuel gauge, and that demon is next!).

I can't find my old sensor so tomorrow I'll buy a new one and try that.
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Old 08-12-2015, 03:27 AM
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Steve, the author of your article is working with air-core gauges. These gauges have coils and he talks in terms of impedance. Your gauges have NO coils and they are totally resistive, using current at an average of six volts. Notice that all your gauges connect to the same CVR.

There is nothing wrong with your OEM setup. It should last for many decades with no maintenance.

Rockauto.com sells three different brands of sending units for your gauge ranging from six to seventeen bucks. Get one.

I'm not sure exactly what you want to do with your gauge but the sending unit delivers the same 10-100Ω resistance that your temp and fuel sending units operate with. Since they use their own CVR, nothing in your electrical system should affect your gauge readings. When you grounded the oil sending unit, you tested your gauge, not the sending unit. That's why the needle deflected. Be careful not to 'inject' 12-volts into your CVR circuit from another power source.

Your charging system runs at about 14.5-volts at highway speeds. At idle and low speeds, your generator (or 1-wire alternator) puts out very little voltage. Know what that does to your CVR? A solid state CVR holds gauge voltage at six, regardless of battery voltage. Mechanical CVRs are all over the map when your system voltage fluctuates at low engine speeds.

I would be more concerned with low oil pressure than high pressure. Modern car manufacturers feel the same. Some shut the engine off if oil pressure drops to zero, and rightfully so for self-preservation. When cranking the engine, your pressure should be at least 5-psi or more. If you really want a precise reading, mount an inexpensive mechanical gauge. - Dave
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Old 08-12-2015, 08:53 AM
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Thanks Dave. I'm going to buy a sensor at O's today and try it tonight.

I used a cheap mechanical gauge when I first started the engine months ago. Remember that Bush's Automotive in Clemmons did the rebuild and we did a lot of modifications to the oiling system. Oil pressure was about 80psi cold high idle using 15W-50 break-in oil, dropped to about 60 on initial hot idle.
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Old 08-12-2015, 10:06 PM
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A cheap BWD sensor and it works. No issues whatsoever when the electric fan turns on, either automatic or manual override.

That's the more expensive Autometer next to the BWD box.
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Old 08-12-2015, 10:29 PM
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Borg Warner has made quality automotive parts for many decades. I'm not surprised yours works as it should.
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Old 08-13-2015, 11:16 AM
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Did they make the gauges?

My son commented on the condition of the wiring in the car. After 50 years and all the abuse this car has seen, the insulation of the wiring, connectors, etc., are in remarkable shape.
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Old 08-14-2015, 03:16 AM
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That's because Essex Wire was here in Detroit. Now the wire harnesses come from Mexico.

Borg Warner made many hundreds of automotive items. I had a Borg Warner 8-track tape deck back in the '60s.
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