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Oil pressure sending unit ground

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dirtyjerseyjeep

NAXJA Forum User
Location
new jersey
Can anyone tell me where the ground is for my oil pressure sending unit ,I'm having issues with my oil pressure and I have a feeling it's working cause it's a new sending unit and my motor runs great.
 
It would be most helpful if you would include the year, engine, driveline information in ALL of your posts.

It makes a HUGE difference if you have an 89 or a 98. If you don;t include this info, you'll find it difficult to get any answers.
 
Agreed... it's very significant especially on this question. Some years ground through the block/threaded tip on the sender, some ground through the wiring harness.
 
Thanks for the info.

I'm not very well versed on post-Renix era Jeeps, but since your sending unit grounds thru the harness, the harness grounds are, for the most part, grounded at the oil dipstick mounting bolt. There is a cluster of common grounds there with a terminal ring. Sometimes the connection there can become loose, corroded or both. Funny that that one spot has so much to do with so many components and it's in about the dirtiest spot on the engine.

Clean the area up, remove the bolt, shine everything up and fix any loose or corroded connections...tighten it all up. It's likely that if you're having gauge issues that the sender is toast.

On the Renix models, the sender is just a one wire, grounds thru the block and when the sender goes south it usually pegs out past 80psi or goes to zero.

On a side note: You can go to User CP and fill in the info on your Jeep in your signature, then it pops up in every post you make.
 
I don't recall exactly where your gauge grounds, but it's definitely through the harness on a 99. Since those senders rarely go bad (the one wire resistive ones are much more prone to failure), I would suspect a ground issue as well.
 
Your '99 oil pressure sensor grounds through the PCM. It's a typical sensor used on your '99 XJ, in that it has a 5 VDC reference voltage supplied by the PCM, a sensor signal to the PCM, and a sensor ground to the PCM.

This sensor ground circuit is spliced into the ground circuit for the TPS, IAT, ECT, CPS, MAP, and others - all terminating inside the PCM.

If you are having oil pressure problems I would suggest checking the oil pressure using a mechanic's diagnostic direct reading oil pressure gauge. These can be rented (money back) from O'reilly and Advance auto parts.
 
Sidewinder CC said:
Your '99 oil pressure sensor grounds through the PCM. It's a typical sensor used on your '99 XJ, in that it has a 5 VDC reference voltage supplied by the PCM, a sensor signal to the PCM, and a sensor ground to the PCM.

This sensor ground circuit is spliced into the ground circuit for the TPS, IAT, ECT, CPS, MAP, and others - all terminating inside the PCM.

If you are having oil pressure problems I would suggest checking the oil pressure using a mechanic's diagnostic direct reading oil pressure gauge. These can be rented (money back) from O'reilly and Advance auto parts.
Click to expand...

I would check the oil pressure with a mechanical gauge as Sidewinder says above. It will at least eliminate that as the source of your problem.

Since your sensor grounds through the wiring harness, I would pull the plug and clean the contacts on both the sensor and the plug, then trace the wire as far as you can, preferably all the way to the PCM, making sure there is no damage to the wire. Also check that the crimps at the plugs are in good shape as that can lead to faulty readings.
 
I'd probably start by unplugging that harness connector from the ECU and measuring from the ground pin on the ECU end to the ground pin on the oil sender end, then check for shorts from that whole wire to the chassis. No need to tear into the harness until you know you have an issue.
 
I think the OP just asked about the ground for the oil pressure sensor since there's so much chatter about grounds relating to the XJ's, not really knowing if he had a ground fault.

It should be known just what oil pressure problems the OP has before suggesting chasing ground wires.
 
Oil pressure is great till it warms up then after its at temp, oil pressure drops to 20 as I'm driving and zero when I stop, motor runs great no Power loss at all, no knocks, Ticks or taps. Sending unit is new from advanced auto.
 
Did you ever figure out the issue? I have a similar issue. I'm 99% sure it's an instrumentation issue, not an actual oil pressure issue. The gauge always reads zero, except if I turn car off...then quickly turn key to on(not start engine) the needle will read for a second...then drop off as actual oil pressure falls. Does it have a separate ground when coming off battery(engine off key on)vs alternator(engine running) power?
 
No, it has the same ground no matter what. 98 down ground the sender through the block, 99 up ground it through the sensor reference ground bus in the wiring harness.

Are you sure that what you're seeing isn't the gauge test sequence on startup?
 
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