Oil pressure switch is different than an oil pressure sending unit.
The switch allows current to pass when pressure is detected from a running engine. This current goes to your choke and opens as the engine warms up.
The sending unit gives an ohm resistance valve as pressure is detected. A bolt/ ohm meter at the unit can tell or at the wire under the dash of the wiring is in question as well.

With it jumping, I would think it’s getting stuck inside and a new unit is best.

 

Oil pressure switch is different than an oil pressure sending unit.
The switch allows current to pass when pressure is detected from a running engine. This current goes to your choke and opens as the engine warms up.
The sending unit gives an ohm resistance valve as pressure is detected. A bolt/ ohm meter at the unit can tell or at the wire under the dash of the wiring is in question as well.

Leaving the oil pressure switch connected to the e-choke is a good thing to have, IMO. Wiring the choke directly to 12v will cause it to open before the engine is running, and could result in hard starts. In essence, the oil pressure switch delays sending current to the choke until after the engine runs (switch closes when OP comes up). If it leaks, use a dab of sealer on the threads.

Hoov

 

To be sure you would have to connect it to a know method.

Either get a mechanical gauge or hook it up to a air compressor with a pressure regulator you can adjust.
That way you can see if the gauge jumps up at a certain pressure instead of smoothly. Use a volt/ohm meter on the sending unit and you can see it it goes up smoothly.
If it does then the gauge is suspect. But I think it's more likely the sending unit.

And as always, check your grounds.

There were two different sending units sold on the CJ. an ohms stest with no pressure is the best way to make sure you get the right one.

 

I think I have a bad sending unit. Given the photos, I think the prior owner (PO) may have t'd off to add another gauge for oil pressure monitoring, but when I go the Jeep it was not hooked up.

When I ground the sending unit (i.e. ground the brown wire) the gauge pegs high-which means a good gauge (I think) . So either a) replace both the sending unit and switch or b) just remove all of if, put back just a sending unit to K.I.S.S. it.

 

That switch with the red wires on the right provides power to the electric choke when the engine is running.

 

I checked that, it does draw power with the key on, but for some reason when I put it on the electric choke, it does not work. When I pull 12v off the alternator, all is good with the choke.

With the oil pressure sending unit/switch- when I pull the brown wire of the oil pressure sending unit, the gauge goes to zero. When I ground out that wire, it pegs to high, so I think my gauge is OK

Think I will just remove all that, get rid of that other switch and wiring, replace it with a new oil pressure sending unit/switch, and that might make this task complete.

Oil pressure sending unit:

https://www.oreillyauto.com/detail/...l-pressure-switch/ps113/5815720/1980/jeep/cj7?q=oil+pressure+sending+unit&pos=3

 

The switch has nothing to do with the gauge. It should only provide power to the choke when the engine is running. Start the engine and check for power at the choke. If so, the switch is fine.

A new sending unit is likely all you need.

Matt

 

This is where you need a voltmeter.

If you measure the voltage at the terminal you will know for sure what the issue is. If you throttle up and don't get a smooth change in the voltage reading, you have a bad sending unit. If the voltage changes with throttle....might be a bad gauge (I doubt that).

Your gauge is basically a current indicating device. The oil pressure transducer (sending unit) varies the resistance to ground as the pressure changes. I used to know what the resistance values were to test the gauge.....basically, you put a resistor from the wire to ground and you could confirm the gauge was working.

You can also use an ohm meter and measure the resistance from the terminal of the sending unit to ground. The resistance reading should change as the oil pressure changes.

 

thanks for the diagnosis procedure with the voltmeter-makes it simpler to follow those instructions.
Seems that it's a bad oil pressure sending unit. I pulled off the old pressure switch and pressure sending unit yesterday evening. On the way home from my real job I'll get a new sending unit, but likely not install a new oil pressure switch as I found a 12v engine on source other than that switch, so it cleans up some wiring in the engine bay. Also one less area for oil to drip from in the future.

 

Just to state it clearly, the oil pressure switch only provides 12v power to the choke when the engine is running and there is oil pressure to activate the switch. So, just before the engine starts the electric choke is fully engaged (closed). After the engine starts and there is oil pressure present, the switch closes and 12v is sent to the electric choke, slowly opening it.

 

Having a 12v source while the engine is RUNNING vs. KEY ON is the right way to go. I do not think I'll run into an issue pulling that source off the alternator as it only will produce volts when the engine is running (albeit it produces 13 or so volts).

 

Which terminal on the alternator do you plan to connect the choke to?

Personally, if the oil pressure switch is working, I'd leave well enough alone. If you are dead set on using the alternator, I'd use the alternator to trigger a relay that would in turn provide full battery voltage to the choke.

Matt

 

And it makes for a good, anti theft device...

Who knows how to operate a manual choke is these days.

 

now showing 40psi on the oil pressure gauge. Ordered the manual choke for the Weber. I think that was the right decision for a simpler/cleaner look.

Now just need to paint that side of the engine. Will probably do that when I replace the plugs/distributor.