Bad Oil Pressure Sender... I hope

[lithium14]

Hey guys. I recently finished my engine rebuild and during one of my drives, my oil pressure gauge suddenly stopped reading (the needle dropped to rest position, not zero). I immediately pulled over and had my Supra towed home.

Note: there was NO CHANGE it how the engine ran, behaved, or sounded. If I had really lost all oil pressure like that, I'm sure it would have rod knocked before I could do anything.

After I got home, I took my oil cap off and lo, there was oil flowing and splashing around like normal. I tested my oil pressure sender by putting the leads of my ohmeter on the signal tip on the pressure sender and a body ground, nothing, no continuity. I made sure the grounds were good by putting one lead on the engine block itself right next to the pressure sender, and behold, perfect continuity.

I also tested my roommates MK3, to see if there was continuity on his 7M between the sender and body, and his had continuity. I concluded that my oil pressure sender was bad.

Does anyone disagree or have ideas?

I posted this thread because I recently received my new OEM pressure sender from Toyota and there was no continuity between the two ends of the sender itself, not sure if that is normal or I got a bad sender...

 

[jetjock]

Not sure why you think there should be continuity but here's an idea: testing things how the TSRM says usually yields better results...

 

[lithium14]

Here's why I think there should be continuity: on a working 7M, there IS continuity, on mine (which isn't working), there isn't. Simple as that. You make it sound like I haven't looked on the TSRM. The TSRM doesn't have anything listed for my problem specifically (as a matter of fact, I even searched on Toyota's online network of manuals/etc for something on specs for what I need). I'm not one of the clueless noobs who creates threads as a first option when I have a problem. I've done everything on my part to diagnose my own problem and have reached my own conclusions. I created this thread to see what the feedback from the community is with regards to my conclusion.

I recognize you are a well-regarded member on this forum and have lots of experience etc, but that post really takes away from your reputation in my eyes and lowers the amount of respect I have for any of your other posts. If you don't have anything constructive to say in my thread, then with all due respect, GTFO.

If there were more than two MK3s in this god forsaken town, I would be asking them for help, but seeing as there AREN'T, I am asking for anyone with 30 minutes to spare, to simply take an ohmeter and test to see if they have continuity between the plug point on the oil pressure sender and a body ground. (only 30 min if you need to take off stuff to get the ohmeter leads down there, if you are super dexterous and can reach down there, then it will take all of 1 minute.)

 

[CyFi6]

There is a section in the TSRM that shows how to test it, it takes some digging to find, its not in plain sight.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=BE&P=42

Not sure if you have seen that, but try doing that test with a test light, it should tell you right away if your sender is bad. Hook up the clamp to the positive battery post and put your probe on the center terminal of the sender with the engine running, the light should flash, if it doesn't then you've got a bad sender.The sender sends a pulsed signal to the bimetallic element in the gauge, so the more oil pressure the faster it pulses and the more the bimetallic strip in the gauge itself bends. According to the TSRM you should have no continuity in the sender with the engine off, so not sure why your buds does.
Its very likely the gauge itself has gone bad as well, or the wiring, so make sure you do those checks too.
Good luck.

 

[jetjock]

Well regarded? You must have me confused with someone else. Anyway, telling you to read the book is not only constructive but one of the best answers you could have gotten. Don't blame me because you suck at this stuff...

 

[lithium14]

Thanks CyFi6. You're right Jetjock. I really do suck at finding shit in the TSRM. Usually I'm pretty good at finding the weird places Toyota puts things (like subframe torque specs under Maintenance.... -_-). Anyways, reading that page reminded me of one thing I forgot about, we tested the senders on the car with the ignition on (the test light deal is exactly the same thing as testing continuity, you're just making sure there is current flowing) which is why the new one doesn't have continuity out of the car... DUH *facepalm

Anyways, I'll report back when I install the new sender.

 

[jetjock]

New ones (or used working ones for that matter) don't have continuity out of the car because there's no oil pressure. If it did the gage would max and burn out when KOEO. There should never be continuity at all times. It appears you aren't familiar with how the system works. Not that you can be blamed since it is a rather quirky design compared to most. Then again most don't have "continuity" either. At least not in the typical sense. My point was, lacking an understanding behind how something operates, it's usually best to use troubleshooting procedures developed by those who do.

That said rather than mess with the sender a simpler method is to disconnect the wire and *briefly* ground it while observing for gage movement. Through elimination that leaves the sender as bad. In that sense it can be troubleshot same as the typcal resistive based system. Just don't leave the gage grounded too long...

 

[lithium14]

Found my problem. It wasn't the pressure sender. It was actually my gauge itself that broke. Hard to explain with words, so I'll post pics later.