Oil pressure sender question

[johnnyc]

Since the Rubicon trip last month, my oil pressure gauge has been pegged at max. It would occasionally drop down, then go back up.

Then today at Big Bear, the gauge would stay at zero. No fluctuations at all. I'm quite sure the oil pressure sender is the problem, since the pump is moving oil.

So I bought a new sender tonight, and now the gauge is pegged at max again.

I did a search and Eagle said to check the sender and the ground. How do I check the ground on the sender?

[5-90]

Continuity check - make sure there is continuity (nearly zero resistance) from the case of the oil pressure sender to the battery "-" terminal, and to the sheetmetal (that's the ground reference for sensors that don't report to the ECU - the ones that do have their own ground.)

If you'd mentioned what year your XJ happens to be, I might be able to give you more advice - there were changes to the wiring over the years.

However, I do believe that if you get continuity between the sensor case and the bolt on the upper firewall that retains the ground strap, you should be in good shape. That's the main chassis ground (the chassis is grounded via the engine block and thence to the battery.) It is usually a good idea to add another ground from the battery, going directly to the sheetmetal of the fenderwell - use a fairly stout cable (8 or 10 gage is fine here) and clean the spot of paint before you screw down the cable. Use Ox-Gard to maintain a clean connection. Unless you're building a Formula racing car, there is no suck thing as too many grounds!

It is also worth noting that the braided ground strap picks up crap, grease, and oil over the years - and that will cause a ground strap that looks alright physically to have a rather high resistance - and cause all sorts of strange problems. When the time comes, I replace that thing with a genuine length of cable, with both ends sealed against contamination - cheap insurance.

I think most of those braided ground straps are good for about ten years - TOPS. After that, they're too contaminated to be reliable. Besides, they're usually aluminum - which isn't as good a conductor as you need for something like this (the better ones are tinned copper - better, but the "open" nature of the conductor is still at issue.)

5-90

[johnnyc]

Cool...thanks. That's a good explanation. It's a 96 (it's in my sig).

Guess I owe you. I'll try to get out to the junkyard tomorrow to look for that pulley for you. :)

[5-90]

Shows how often I actually READ sigs - even tho I try to change mine every few months or so...

I'll see if I've got a 1996FSM - I've got a 97 (which is probably close) and I think I've got a 1994 - but I'd have to check.

5-90

[Yucca-Man]

Make sure you didn't put anything on the threads when you installed the oil pressure sender. Plumber's tape, etc will break the ground that the sender needs to operate properly and on the 96 the gauge will show MAX if the wire is disconnected or the sender does not properly ground through the threads.

[Eagle]

Make sure you didn't put anything on the threads when you installed the oil pressure sender. Plumber's tape, etc will break the ground that the sender needs to operate properly and on the 96 the gauge will show MAX if the wire is disconnected or the sender does not properly ground through the threads.
And if you remove the wire from the sender and ground it directly to the engine block, the needle should go to zero.

Renix models should be the opposite -- open circuit +0, grounded = max.

[johnnyc]

Thanks Yucca and Eagle.

No, I didn't put anything on the threads. You say the sender is grounded through the threads? Because the threads are plastic, aren't they?

I replaced the ground strap as 5-90 suggested. It was kinda thrashed, so I'm glad I did it. But it didn't help the gauge situation. And all of the other grounds checked out okay.

[Eagle]

Because the threads are plastic, aren't they?
Nope. Metal

[JEONLYEP]

Should be metal. Just something to think about (or for others to think about) it was cheaper to buy an after market gauge. It was more work to install, but I trust it more.

.02

[5-90]

Something I forgot to mention - I've been using a small amount of RTV Copper on my self-grounding sensors in liquid baths, with no trouble.

There's just enough copper in the RTV to allow for conductivity (which is probably what it's designed for,) and it helps the pipe threads - which aren't designed for dry sealing anyhow.

It doesn't take much - I probably put a little on the first two or three threads, and screw it in (so it's probably grounding on the larger threads) but I selected the "copper" because I figured that colour wasn't BS.

It doesn't take much, but just a little will help, and using the RTV Copper hasn't interfered with the grounds so far (I've been doing it for years...)

5-90

[johnnyc]

OK, sorry to bring this thread back. But I've still got the same problem.

I've replaced the braided ground strap, checked all ground connections, checked to make sure the sender threads are indeed metal, and replaced the oil filter.

I also did as Eagle said and grounded the connector, and the gauge did go to zero. I also tried to run a jumper wire from the sender case to a different ground, but the gauge remained pegged at max.

So what is left? I figure the new sender could be faulty. Or the gauge itself. Right now, I'm to the point where I'm trying to find a good place to mount some aftermarket gauges.

[langer1]

I think there's a sender for a light and one for a gauge, could you have the wrong one?

[johnnyc]

I believe there are two senders available. One is for vehicles that only have idiot lights and the second is if you have full gauges. I'm 99% sure I have the correct one, as all websites list the same part number.

Thanks though.

[Kejtar]

I believe there are two senders available. One is for vehicles that only have idiot lights and the second is if you have full gauges. I'm 99% sure I have the correct one, as all websites list the same part number.

Thanks though.
Actually I think you might have the wrong one afterall. How many pins do you have coming out of the fuel sender? One or two?

[johnnyc]

One...just like the original one.

[Kejtar]

One...just like the original one.
Hmmm, that's odd. What you can do is take off the connector and hookup a meter to it and ground the other lead. Then have someone rev up the engine and see if the resistance on it changes or is it constant. If you need help with that, stop by my place and we can take a look at it.

[johnnyc]

Thanks Remi...

[Eagle]

The sender for the idiot lights is just a switch. Connect that to a gauge and the gauge will read either zero, or 80. The correct sender is a variable resistance unit.

[Kejtar]

The sender for the idiot lights is just a switch. Connect that to a gauge and the gauge will read either zero, or 80. The correct sender is a variable resistance unit.
That's why I want to hook it up to a multimeter :D

[JEONLYEP]

FYI an 1 1/2 inch gauge will fit in place of the stock gauge, on a 91 anyway.

It's not pretty, but I don't care. I'd rather have a gauge that I trust.

http://users.ucom.net/~werwe/03.jpg

Daryl