ruralandalone Posted July 7, 2022 Share Posted July 7, 2022 86 mj My oil pressure guage does not work properly, and I can't diagnose it. It reads high all the time. I got out my troubleshooting manual. First step. Disconnect the sensor, and the meter should read high. Check Seconds step. Ground the wire, and it should read low. Check. If it does, Third step: replace the sensor. Check Result: It still reads high. T o my way of thinking, assuming that the brand new sensor is good, somehow the electrical circuit is open, but I can't see how it could be. The only place I can think of is that the sensor itself is not properly grounded, and that seems, well, impossible. I'm open to suggestions as to what else I can try, or should look at. I mean, there i s really is only the guage (which seems to be working) a wire, and a sensor.... Link to comment Share on other sites More sharing options...
gogmorgo Posted July 7, 2022 Share Posted July 7, 2022 Have you confirmed the reading on the gauge with a mechanical gauge? Link to comment Share on other sites More sharing options...
ruralandalone Posted July 7, 2022 Author Share Posted July 7, 2022 um. no. I don't have a mechanical guage suitable for the purpose. I guess that would be logical. Any idea where I can source one? Or for that matter, what the oil pressure SHOULD be? Logically, I assume that either the sensor is mismatched to the guage, the oil pressure is too high, or the new sensor is defective. I don't know what else it could be. Link to comment Share on other sites More sharing options...
Ωhm Posted July 7, 2022 Share Posted July 7, 2022 Connect ohmmeter between oil pressure sender terminal and battery ground terminal. Resistance should change with change in oil pressure. Note values. I might have a spec sheet somewhere. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 7, 2022 Author Share Posted July 7, 2022 That I can do tomorrow morning. I'll let you know. That will tell me if the sensor works, but not too much else. I did (just for fun) put the ohmmeter on the 2 spare sensors I have at the bench. Got different values, but since I don't know what they should be, not terribly useful. I did come across this on 4x4wire.com, which applies to CJ's. Not positive the numbers are the same Pressure (PSI) Resistance (ohms) 0 234-246 20 149-157 40 100.5-105.5 60 65-69 80 32.5-34.5 Link to comment Share on other sites More sharing options...
ruralandalone Posted July 8, 2022 Author Share Posted July 8, 2022 I tried this morning with 2 of the sensors. I'm not sure what the results tell me, but either all of the sensors (including the new one) are bad, or the oil pressure is way too high. I am ordering a mechanical gauge, as that would seem to be the only way to get to the bottom of this. both sensors went to an open circuit when I started the engine. Link to comment Share on other sites More sharing options...
Ωhm Posted July 8, 2022 Share Posted July 8, 2022 1987 Electrical Manual Link to comment Share on other sites More sharing options...
ruralandalone Posted July 8, 2022 Author Share Posted July 8, 2022 Thanks. I should have a mechanical gauge next week to verify where the problem lies Link to comment Share on other sites More sharing options...
zomeizter Posted July 9, 2022 Share Posted July 9, 2022 You mentioned that both sensors went to an open circuit when engine was started, probably means those are pressure switches not pressure "senders" IAW the diagram by Ohm... Link to comment Share on other sites More sharing options...
ruralandalone Posted July 9, 2022 Author Share Posted July 9, 2022 well, they are the proper replacement part listed on rockauto, but you could well be right. Or at least partly. The part is listed as an oil pressure sender/switch. I think the question is whether the oil pressure is high enough to go past the "sensor" pressure and then switch. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 9, 2022 Share Posted July 9, 2022 The switch is switched on when there’s a certain amount of pressure and it keeps the light off. When there’s low pressure the switch turns off and the light circuit grounds out and turns the light on. The sensor will read accurately. Do you have a short little stubby thing or a big fat sensor?(or tall and skinny, depending on the sensor you bought) Link to comment Share on other sites More sharing options...
ruralandalone Posted July 9, 2022 Author Share Posted July 9, 2022 short and stubby. all 3 read differently Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 9, 2022 Share Posted July 9, 2022 1 hour ago, ruralandalone said: short and stubby. all 3 read differently Yup!!! That’s the switch. As stated you need the sensor which can be had from Chrysler or aftermarket I’ll get a part number here in a minute for you. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 9, 2022 Author Share Posted July 9, 2022 well, that would explain a lot. I guess the wrong item was put in or the instruments were changed by a previous owner..... Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 9, 2022 Share Posted July 9, 2022 56026782AC is the oil sensor part number. Still available from Chrysler. It sounds like the PO probably thought it would swap over and all would work. Course that asks a new question. Does the water temp reflect any data or does it just stay at the first bar? Link to comment Share on other sites More sharing options...
ruralandalone Posted July 9, 2022 Author Share Posted July 9, 2022 One issue at a time, please! :) IF I understand you correctly, the "sensor" is either a sensor or switch. OR perhaps both. What I likely have is a switch, indicating oil pressure is present. What I need is a SENSOR, which had variable resistance. Interesting that Rockauto does not differentiate between them, as they are listed together, and none of the parts listed provide operating specifications as to resistance values. I (in my ignorance) thought that the different styles were a matter of design, not function My mechanical gauge is on its way to me, so I will be able to verify next week. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 9, 2022 Share Posted July 9, 2022 Fair enough. But yes there are two different parts available. The switch, which you currently have and the sensor. The switch is for the idiot light cluster and the sensor is for the gauge. It probably didn’t help that the PO didn’t get the right part in the first place which sent you on this mad tangent. Here is what the correct sensor should look like: I kinda forgot we had one on hand here at work. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 9, 2022 Author Share Posted July 9, 2022 Thank you very much for the information! Most helpful. I'll order the right part, AND check with a mechanical gauge. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 9, 2022 Share Posted July 9, 2022 No problem. That’s why we’re here for. Hopefully the mech gauge will reveal a healthy engine. Link to comment Share on other sites More sharing options...
ruralandalone Posted July 9, 2022 Author Share Posted July 9, 2022 I'll report back next week on my findings Link to comment Share on other sites More sharing options...
ruralandalone Posted July 14, 2022 Author Share Posted July 14, 2022 I got my mechanical oil pressure gauge today. I have not checked the warm engine, but I have about 55 lbs for a cold engine. If anyone can advise as to what decent numbers are, I'd appreciate it. My CORRECT sensor showed up late today, so it goes on tomorrow. Today I replaced my fuel sender and pump. I now have a working fuel gauge. I'm making progress! Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 14, 2022 Share Posted July 14, 2022 55psi at cold is healthy. That’s what mine runs at. Link to comment Share on other sites More sharing options...
AZJeff Posted July 14, 2022 Share Posted July 14, 2022 Factory spec. for a 4.0 is 13psi minimum at hot idle, and 37psi minimum above 1600 rpm. (This assumes using the recommended 10w30 or 10w40 oil.) Here in AZ, in the summer, the oil pressure on the 4.0's I have owned isn't really very high when the engine is REAL hot, generally being about 40 psi at road speeds. (Underhood and pavement temperatures in Phoenix are something everyone should experience to see how oil pressure drops down as the engine heats. Link to comment Share on other sites More sharing options...
AZJeff Posted July 14, 2022 Share Posted July 14, 2022 1 minute ago, eaglescout526 said: 55psi at cold is healthy. That’s what mine runs at. Yeah, but what is it when idling in traffic this afternoon on the way home, when it's 107*? Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 14, 2022 Share Posted July 14, 2022 25 minutes ago, AZJeff said: Yeah, but what is it when idling in traffic this afternoon on the way home, when it's 107*? Lol. Mine is usually about 30psi at idle during the heat. I’ll have to check now as I never really payed attention when I get home. Link to comment Share on other sites More sharing options...
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