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1 Bar Pressure After Oil Change

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Old 12-19-2017, 05:56 PM
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Coloradoguy
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Default 1 Bar Pressure After Oil Change

I've searched other threads and can't seem to find an answer to my oil pressure problem, if that's what it is.

I changed the oil on my 86 944NA. Used a new K&N oil filter. Cranked it up and she runs smooth and well, but it seems I've got only 1 bar oil pressure and the warning light is on.

No tappet noise.
Idles perfectly.
Oil on the dip stick.
Wires going to pressure sender are tight.

I've read at Clark's Garage about the oil pump possibly losing its prime. Could this be the case here?

Two issues which may be factors: The car is still on jack stands in front. Could this angle be effecting things? Also, before starting, I disconnected the main lead to the distributor and cranked it a few times in order to prime the system. I've done this before on other cars I've owned with no ill effects; could I have fried something?

UPDATE: I removed the oil filter and tried priming the pump ala Clark's Garage but no dice. I only rotated the engine maybe one revolution. Maybe not enough? Also, It's difficult to fill the oil WHILE turning the crank counter clockwise.

EDIT: I've removed the spark plugs and the DME and tried cranking it without success. I cranked for ten seconds with a 30 second rest between. I did this 4 times. After seeing that the oil feed tube coming into the filter housing was full of oil I'm thinking that the oil pressure switch itself may be at fault. The fact that there was absolutely no valve or lifter noise when I initially started it up after the oil change keeps me thinking that I actually do have oil pressure. Why the sender would suddenly stop working after an oil change is a mystery, but I did put some rags under the housing to catch oil when removing the filter so perhaps I damaged it somehow; the connections both looked good. I'll update with results.

Last edited by Coloradoguy; 12-21-2017 at 02:51 PM.
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Old 12-21-2017, 04:57 PM
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Perhaps this thread can help https://rennlist.com/forums/944-and-...der-issue.html

Would try testing the oil pressure sender/switch before anything, sounds like it's gone bad.
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Old 12-21-2017, 07:24 PM
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Thanks for that, mr4x4.

I went ahead and ordered a new pressure sensor and will install it once it arrives. I'm curious to see how much oil -- if any -- gushes out when i remove the old one. Our weather just changed from 65 degrees to 17 with snow and I don't really feel like laying around in an unheated garage to do the testing necessary on the old one.

As I stated above, the absolutely wonderful purring of the engine after changing the oil leads me to strongly suspect that the trouble lies with the sensor rather than any real issue with the oil pump.
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Old 12-21-2017, 07:27 PM
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Ok cool tell me how that goes, it's something that I might have to change in the future as well.
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Old 12-22-2017, 01:37 PM
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Will do. With the holidays the part won't arrive until December 26th so it's a waiting game.

Researching this topic it seems like 99% of the posts dealt with loss of oil pressure after a rebuild. Since I merely changed the oil, I can't see why that would completely drain the pump.

I'm hopeful that a new oil pressure senor will fix my problem, because of this post: http://www.944online.com/cgi-bin/yab...num=1328734487 Relevant quote: "Trust me if you have 0 oil pressure the sound of your motor will let you know." Mine when started sounded great...

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Old 12-23-2017, 10:00 PM
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connect an ohm meter, analog, if you have one, to the sender and ground. resistance should go up as pressure increases. Mr Fletcher has the late and early charts posted under senders, electrical 19
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Old 12-23-2017, 10:35 PM
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The only ohm meter I've got is digital, unfortunately, and as the pressure currently stays flat then I don't see how the ohmmeter would say anything different.
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Old 12-23-2017, 11:05 PM
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if the sender reads correctly but the gauge reads 'flat', there may be other issues.
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Old 12-24-2017, 04:17 PM
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Thanks for the suggestion, but seeing as how I don't have an analog gauge combined with overnight single digit cold and an unheated garage and a new sender supposedly arriving the day after Christmas I'm currently planning on plugging in the new one and seeing if that fixes my problem. If not, then I'll start measuring resistances.

Fingers crossed...
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Old 01-07-2018, 05:19 PM
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So no joy. Installed a oil pressure sensor and gauge still reads zero pressure. The engine sounds good, and there was oil coming out of the sender hole when I took the old one off so I'm fairly certain that I do have pressure.

I checked the resistance with the engine off. The G terminal reads 011 connected to the blue/white wire and 003 on the WK terminal connected to the spade connection on the blue wire.

Took the 14 pin connector apart and squired it with electrical contact cleaner. Couldn't get any resistance readings from any of the contacts. This struck me as weird. So I bought some test leads and am going to measure the resistance from the G terminal to ground while the engine is running. It should read high, and if it does, then I'll know the problem lies somewhere between the sensor and the dash gauge.

Stay tuned...

Measured the G terminal and only got intermittent readings while the engine was running. The Blu/Wht lead was still connected while I tested it (IS THIS CORRECT?). It read around 184 for a second or two; then nothing. Once I turned the engine off, it would settle back to 14.1 and read constant. My replacement sensor is one of those $27 Uro ones. Am I correct in assuming that my problem lies with my new but apparently erratic faulty sensor?

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Old 01-09-2018, 12:06 PM
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Ordered a OEM sensor which should be here by Friday. Regardless of what my testing shows I want a VDO unit in there instead of rolling the dice with the Uro. Sometimes saving money results in just the opposite.
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Old Today, 01:16 PM
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Just to finish up if this thread turns up on a future search.

The issue turned out to be a not-so-small plastic-like piece wedged in the oil pressure relief valve, keeping it open. I thought that I had oil pressure since the tappets weren't making much of a racket, but a pressure gauge confirmed that oil pressure was zero.

Why the OPRV managed to get jammed open exactly when I did an oil change is a mystery, but I'm just glad that it got wedged where it did; a blocked oil gallery could have been a nightmare!



Also, the green o-ring was missing from the end of the valve, so I'm glad I was able to replace it when taking it out for inspection.

Lessons learned (or relearned):

Don't ignore the obvious.
Take things step by step.
Proper tools (in this case, a pressure tester) are worth every penny.
Don't assume that you know more than you do.
Move from the simple to the complex.
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