Oil pressure sending unit

[joeye]

Is there any way to check if the oil pressure sending unit is working correctly. O.P. usually runs around 45 - 50, now all of a sudden is pegged at the end. Don't believe it is really an oil pressure issue.

Joe 74 Cherokee sport

[serehill]

you can look up the oil pressure resistance in the TSM's & check it running & not running. Most likely the wire is shorted. Disconnect the wire & see if it clears the gauge. If the gauge stays pegged then it's most likely a short in the wiring.


http://oljeep.com/

[tgreese]

It's easier to check the gauge with resistances. This is what the FSM advises. CHeck the guage and if it checks ok, replace the sender.

Page 3-47 here: http://oljeep.com/gw/74_tsm/3-Electrica ... End%29.pdf Step-by-step instructions.

[serehill]

I'm Confused I suppose. Different strokes for different folks. If you pull the wire off the sender & it stays pegged. Or if you pull the wire off & it goes to zero why would you check the gauge at that point it's still possibly the wiring or the sender. Yes no reaction could be the gauge. It's 50/50 at that point. Further process of elimination. If it stays pegged & you disconnect it at the gauge & nothing happens then I would check the gauge since it was proven faulty. It seems to me it would be easier to find out what the problem is by localizing it before you start testing individual pieces. If you can localize the issue then there's a lot less random testing. In my experience a bad gauge is more likely to zero as opposed to peg. With exception of the lat models which this isn't. A resistive circuit characteristically looses resistance instead of gaining it. I would double my suspicion if the meter goes to zero when the key is turned off.
Nothing can be easier than pulling the wire off the sender to check reaction. I don think the TSM is stating it's easier to do one than the other. It's seems to be assuming there's something wrong with the meter first. I'm saying you can track & narrow down the issue because removing the meter to test is not easy. Yes you could simply add resistance to the same wire you disconnect to ground without disassembly. That would test everything from the sender to the gauge. 6yhat all seems to be a lot easier than the TSM.

Just my opinion & process.

[letank]

As said above, it is a lot easier to pull the wire

open circuit, infinite resistance / wire disconnected will read 0 pressure,
No resistance, grounded wire will read maximum pressure, in fact for our gauges 10 ohms is 80 psi.

you can disconnect the wire gauge at the sender and connect an ohmmeter on the sender and the other prong to the battery or engine ground, start your engine and read the numbers, 25 ohms is about 40 psi, and 70 ohms about 10 psi. This is the quick and dirty.

As written in the TSM put a known resistance between the oil sender wire and the engine or battery ground and see what the gauge shows,12 ohms 80 psi, 25 ohms 40 psi, and 70 ohms about 10 psi and , if the gauge does not give the right numbers, time to change gauge.... in fact not really, make sure that the temp gauge gives the same numbers changing the readings from low ohms to high temp, mid and high oms for low temp... if the temp gauge is as inaccurate as the oil pressure gauge... it is probably the voltage regulator built in the coolant gauge that is bad... and probably your gas gauge is off as well.

This is my ohm test device

[joeye]

I'm Confused I suppose. Different strokes for different folks. If you pull the wire off the sender & it stays pegged. Or if you pull the wire off & it goes to zero why would you check the gauge at that point it's still possibly the wiring or the sender. Yes no reaction could be the gauge. It's 50/50 at that point. Further process of elimination. If it stays pegged & you disconnect it at the gauge & nothing happens then I would check the gauge since it was proven faulty. It seems to me it would be easier to find out what the problem is by localizing it before you start testing individual pieces. If you can localize the issue then there's a lot less random testing. In my experience a bad gauge is more likely to zero as opposed to peg. With exception of the lat models which this isn't. A resistive circuit characteristically looses resistance instead of gaining it. I would double my suspicion if the meter goes to zero when the key is turned off.
Nothing can be easier than pulling the wire off the sender to check reaction. I don think the TSM is stating it's easier to do one than the other. It's seems to be assuming there's something wrong with the meter first. I'm saying you can track & narrow down the issue because removing the meter to test is not easy. Yes you could simply add resistance to the same wire you disconnect to ground without disassembly. That would test everything from the sender to the gauge. 6yhat all seems to be a lot easier than the TSM.

Just my opinion & process.

That was kind of my thought. Thanks for the info. Since I don't drive it very much, I'm not that worried. I do believe it could be the wiring, since before it stopped working (pegging) every once in a while, it would peg up at 80 and then after a little bit, it would go down to its normal 40ish and function correctly. Next time I fire it up I will pull the wire off the sending unit, since it only takes a minute anyways and if the needle stays pegged, I guess it the wiring.

[Little Green]

Mine does this every once in a while. Gets pegged all the way to the top then other times it works perfect. If I unplug the wire from the unit and scrub it it sometimes works better. I think it's just a crappy electrical connection at that point and not necessarily something wrong with either the gauge or the sender, just a poor connection. Try crimping the connector a tad and reconnecting it to the unit itself. Mine just gets loose over time.

[carnuck]

A bad ground to the body can affect the gauges as well. The feedback causes the bimetal dash voltage regulator to stick and shoot up. I added a ground wire to the corner screw of the circuit board (which is supposed to be grounded) to my dash's metal frame. I had already added an extra body to battery negative ground wire which fixed a lot of other issues.