Oil pressure sensor on 401

[merrill77]

I suspect a bad sensor...and it had a questionable looking connection - a push-on connector on a button-like knob on the end of the sensor. What I got from Autozone had a post with nuts, so I soldered and shrink-wrapped a ring connector on and installed the new sensor.

Now instead of reporting oil pressure that seemed a little on the low side...the dash gauge reports nothing. The needle doesn't move at all I'm pretty confident in my wiring skills. Not so much with the wrenching skills.

So next, I took a closer look at the box they gave me...and also queried the part on the Autozone website. They list two parts: PS151 and PS32. The former is $30, the latter is $15. The latter looks like the one that I took off the motor...the former is what they gave me to replace it with. I find it odd that it is listed as an "oil pressure switch", since it doesn't switch anything.

These are them:
https://www.autozone.com/external-engin ... 45262_8450
https://www.autozone.com/external-engin ... 22823_8450

Did they give me the right part? Anyone know the difference between the two?

Next question. I found the sensor attached to an arrangement of brass fittings that I found rather odd. Is this how it is should look?
(picture is looking up from below - the kinda goldish-looking thing is the "oil pressure switch". To the immediate left, you can see the threads for the oil filter. Exhaust manifold to the immediate right).



TIA!
Chris

[az chip]

Someone put extra stuff on there. Different oil pressure transmitters for different vehicles. Check NAPA. My stock pressure gauge is sluggish and reads low. I installed a aftermarket transmitter and gauge that I trust a lot more. Is your your transmitter 1/8 NPT?

[derf]

The oil pressure switch I believe is for the choke heater. You want the pressure sending unit.

[csuengr]

There actually something called an oil pressure switch. GM used a bunch of them. All they do is tell the driver there is oil pressure, but not how much pressure. It was also used as part of the fuel pump circuit.

I suspects that AZ just calls any oil pressure sensor an oil pressure switch.

[tgreese]

Couple of points - First, you'd think that "switch" would mean on-off, but the gauge sender is not on-off, but a variable resistance. Unfortunately Autozone calls both a switch... I recommend you take any third-party online listing with several grains of salt. Online listings for Jeep are rife with errors.

Jeep did use an on-off oil pressure switch for the choke on some models. Is this in the '77 or '87 chassis? They will need different senders. You need to match the part to the chassis, not the engine.

I've noticed that the aftermarket parts suppliers do not pay a lot of attention to the connection type when they write their application info. The original sender probably had a threaded end with a push-on connector. The button terminal seen on the Autozone part is meant for a flat push-on connector, and is quite unreliable IME. The stud can be used with the OEM push-on connector, or a couple of nuts and a ring connector.

Before I bought a sender, I would test the gauge circuit with fixed resistors. The TSM has a section about this. Jeep spec's a special tester, but it's just a box, switch, some fixed resistors and alligator leads. A fixed resistor and a couple of clip leads will dot he same thing. Test the gauge, then get a sender that matches the resistance range of the gauge. The RockAuto listings will tell you a lot more than the Autozone listings - RockAuto shows this one http://www.rockauto.com/en/moreinfo.php ... 13&jsn=463 for a '77 as well as a Standard and another Airtex part, both with the flat connector.

The factory parts book shows a 3212004 for a 1977 FSJ. This crosses to a Standard part - http://www.rockauto.com/en/moreinfo.php?pk=44334&jsn=12

[weeegoneeer]

They changed oil sensors in '86 I believe at the same time they refreshed the gauge cluster. When swapping my motor from my '87 to the '84 was freaked out that I wasn't seeing oil pressure on the gauge, verified pressure with a mechanical gauge, then swapped out the sender from the old motor and read fine. Wonder if they gave you a newer sender?

Also - that teflon tape on that brass piece isn't helping the ground needed to get a reading. I made that mistake too. Using no teflon now and I don't leak, if you feel the need to use teflon just put one turn on it so you're sure the thread will bite through and give you a ground.

An oil pressure switch looks different than those links & has a connector with more than one wire. Not sure why they listed it as a switch.

~j

[az chip]

There actually something called an oil pressure switch. GM used a bunch of them. All they do is tell the driver there is oil pressure, but not how much pressure. It was also used as part of the fuel pump circuit.

I suspects that AZ just calls any oil pressure sensor an oil pressure switch.

I may have if I was tired. And I have been lately. But you would suspect wrong. Check my post again. I know the difference.

[merrill77]

I think AZ meant AutoZone, not 'az chip'.

[az chip]

I think AZ meant AutoZone, not 'az chip'.

OHhhhhh..lol. 15 hour work days for 2 weeks not conducive for comprehension.