oil pressure gauge dilemma

My XJ came with idiot lights, and I did some research and found out I could put a pod in that has the gauges. I just had to replace the temp. sending unit, and the oil pressure sending unit. I went and got the sending units, got the pod at the junkyard,(for anybody in the NH area looking to do this project, there are about 4-5 XJs at Lamberts on rt. 125 that have the gauge pod) and went to install everything. I did the temp first. What a pita. Theres almost no room to work with. The temp gauge works now though. Before I removed the oil pressure s.u. i tried locating the connector. Mine, for the idiot lights, has a single flat connector, whereas the new one has an oval hookup with 2 round pins. WTF?? I looked around and there are no extra hookups dangling off the wire. Is there any difference between the 90 and 91 model years in this respect? I'm all confused.

EvilCherokee said:

Before I removed the oil pressure s.u. i tried locating the connector. Mine, for the idiot lights, has a single flat connector, whereas the new one has an oval hookup with 2 round pins. WTF?? I looked around and there are no extra hookups dangling off the wire. Is there any difference between the 90 and 91 model years in this respect? I'm all confused.

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Yes, there is a difference. The dealer or parts house sold you the wrong sender. I assume you have a '90 or earlier XJ. Take the sender back and ask for one for a '90. Should have one flat connector.

nope, mine is a 91. is it possible jeep used some 1990 components? i figured since just about everything on there that i've installed like the temp sending unit was for a 91, the oil pressure sending unit woulda been for a 91. i have definitely been wrong before. my mom has an 88 Suburban. when i went to replace the water pump, got home with the part and it wasn't even close. went back with the old one, and found out that i needed the water pump for an 87.

I know Chrysler reversed the polarity of the instruments in '91. Of course, resistance is resistance and a resistor doesn't much care which way the elctrons flow, but Chrysler also changed the resistance value. 90 and earlier are 0 - 88 ohm, '91 and up are 0 - 104 ohm. The newest I have in that range is an '89 and that takes a sender with a single, flat connector.

I don't know what the connection should be on a '91. Is it possible they sold you a sender for a newer (ODB-II) XJ?

Consider the possibility that since the idiot light sender is just a switch, some previous owner put in a generic switch and snipped the connector. If this is the case, then the dealer may have given you the right switch, but you'll need to fudge the connection or get a new connector.

You might be able to make a quick test. Without bothering to install the new switch, make a temporary connection with the body of the sensor grounded, and the connecting wire to the operative terminal of the sensor (only one pin on that two-pin connector is connected internally, I think). With ignition on, if the sensor is correct, it should read zero oil pressure. If a 91-up sender system is disconnected, it will read off-scale, and I believe that if it is the wrong sender it will also read off-scale. I can't guarantee this, but I think if you get a zero reading, it's worth putting it in, bodging a temporary connection, and trying it with engine running. If it gives a pressure reading then, you can go ahead and connect it properly.

edit: You can also very easily test whether your system is the 91-up, sinply by disconnecting the sender wire as it now is. If the gauge runs off scale then it's a 91-up. If it drops to zero it's the old style.

Do you have experience with a Pre-1991 XJ that you base this advise on?

I have a 1990 and two 1987 XJs. I recently had an oil pressure sender fail open on the 1990 and one of the 1987s. I can't speak for the 1991, but I can say for sure that the guage goes railed to high when the senders (or the connecting wire) opens with a 1987 to 1990 XJ.

went to VIP today. the sending unit for an XJ with gauges is a warehouse only item. so i went to Autozone, and sure enough the sending unit for a 1990 XJ matches. what a pita.