oil psi gauge in-op

[Joshooha]

This is for you electrical gurus. This can be applied for anyone with a cherokee as well.

 

'89 MJ 5spdmanual/4.0litre

 

full gauges (factory)

 

The oil psi gauge has been pegged, well above 80 psi, and has not worked since I purchased the MJ. I replaced the sending unit with the correct one for a full gauge set (not the dummy light sending unit). This didn't cure it. So, I swapped the gauge from my XJ into the cluster, and it did the same thing, just pegged above 80. Obviously I checked oil PSI and its right at 35-40#.

 

SO, where do I need to chase wires to? Seems to me we have a short to ground in the CKT, but I would like some of yall's opinions!

 

I have been rocking it like this for about 9 months and sick of hooking up a manual gauge to it periodically to make sure everything is kosher.

 

[HOrnbrod]

Yes, you most likely have a ground between the oil pressure sensor and the + terminal of the gauge. I'd look up the correct pin numbers for you, but I don't have an electrical FSM for your year. You need to check for continuity between the male cluster connector to the sensor, and from the female cluster receptacle to the gauge. The cluster foil can sometimes cause this too. I have plenty of these around and can send you one for postage if you need.

 

EDIT: Instead of relying on memory, I checked the FSM. If you have an pegged oil pressure gauge it's caused by an OPEN (not ground/short). :doh: Should know by now not to rely on memory anymore. Same procedure though, check for continuity from point to point using the FSM schematic between the sender and gauge, and find out where the open is. Again, could also be the cracked cluster foil causing the open.

[1987Comanche]

You need to find the point of high resistance in the circuit. If I remember correctly no resistance (0 ohms) = 0psi and 100ohm=80psi on the gauge. You may find frayed insulation, corroded connector, etc.

I suppose it's possible that the oil feed port is physically blocked. If you remove the sender and run the engine for a few seconds without it do you get a decent stream of oil from the port? Perhaps you'll blow out a chunk of carbon in the process. This is what caused my gauge to act erratically.

[Eagle]

Yes, you most likely have a ground between the oil pressure sensor and the + terminal of the gauge. I'd look up the correct pin numbers for you, but I don't have an electrical FSM for your year. You need to check for continuity between the male cluster connector to the sensor, and from the female cluster receptacle to the gauge. The cluster foil can sometimes cause this too. I have plenty of these around and can send you one for postage if you need.

 

EDIT: Instead of relying on memory, I checked the FSM. If you have an pegged oil pressure gauge it's caused by an OPEN (not ground/short). :doh: Should know by now not to rely on memory anymore. Same procedure though, check for continuity from point to point using the FSM schematic between the sender and gauge, and find out where the open is. Again, could also be the cracked cluster foil causing the open.

I think the sender is connected to the negative terminal of the gauge. Should be easy enough to run a temporary jumper directly from the negative terminal of the gauge to the sender and see what happens.

 

Even easier -- start the engine, remove the wire from the terminal on the sending unit and ground it directly to the block, and see if the needle drops to zero. If so, the wiring is good. If not, there's a break in the circuit -- or the gauge itself is fubar.

[HOrnbrod]

I think the sender is connected to the negative terminal of the gauge.

Possible. Have to check it out with the Renix' cluster foils; for sure the HOs go to the + terminal.

 

Even easier -- start the engine, remove the wire from the terminal on the sending unit and ground it directly to the block, and see if the needle drops to zero. If so, the wiring is good. If not, there's a break in the circuit -- or the gauge itself is fubar.

Don't think the wiring is good based on the OP's symptoms.

[Joshooha]

thanks for the responses guys, your all on the same track I was headed. I will start tracking it down hopefully next week. I'm in the process of doing some suspension work to the XJ right now!