Crumpler

Ok gentlemen. Looking for best plan of attack with this one.

Back story was I had been on the road without issue for about 25 min.
Then got flashing central warning.
Oil pressure indicator was on. Gauge was at zero bar at idle and 2 bar if throttle.

Side of the road check showed things intact, no leaks and almost full on dipstick.

I was about a mile from home, and with increased rectal tone started up and drove it the rest of the way hoping it was electrical and not real.

So far I have:
adequate oil level (close to top mark cold).
pressure sender intact and connections good.
oil cooler lines intact.
No leaks anywhere.
No oil in intake (well its an S3, so minimal in side plenums.


Traditionally this car is pegged on cluster oil gauge at all times when running -- unless run hot and foot on brake then I get a reading of 3 bar or so. I chased this down several years ago and replaced pressure sender, R/R on cluster and even new printed circuit did not make a difference.

Timing belt is intact (running fine, tracking fine), I never read about an oil pump failure, is that possible?

Restarted it to confirm and no warnings but still running at 2 bar.

What is spec. to test pressure sender?
What else should I be looking at?
Last work done was that shot at crankcase vent system that didn't pan out, and converted back to stock.

Ducman82

wonky sender contacts if ya ask me. or a sender.... so odd...hmm

FredR

If you have an indicated pressure of zero at idle and the central alarm is going off then at face value that looks rather ominous [sad to say]. If those two things were to happen on my motor the first thing I would do would be to switch it off there and then until I found the cause. With two different indications running concurrently it tends to suggest the readings are legitimate but nonetheless first check I would do is take a look at the condition of the wires in the engine wiring harness. If these are original supply then they are probably shot. If the oil pressure indication was permanently pegged that might indicate an earth fault. Mine pegs when cold and drops to 5 barg when fully warmed up and running 3k rpm plus. At idle it shows 2 barg. Whereas both wires could be faulty the chances of them both showing fault condition at the same time must be slim but not impossible. Take a look at the cores in the engine harness as they enter the 14 pin connector next to the hot post- specifically identify the two cores carrying the signals from the oil pressure sender- you may find the insulation is falling off/crumbling. Then of course the sender.

Anything mechanical can have problems and the oil pump is no exception albeit failures [thankfully] are very rare.

If you can prove the indications you saw are genuine, where you go from this point will doubtless get some interesting responses. First suspect might be some kind of partial failure in the pump suction line given you appear to be generating a little pressure with revs - someone once left a piece of cloth in the sump and it partially blocked the inlet. If the bolts holding the suction come loose [have you had them off at all?] then some suction head will be lost causing some potential to get progressively worse and total failure at some stage. A failed spring in the pressure relief valve might also cause something along the lines you are seeing.

Hopefully it will be something silly like the wiring and easy to resolve but....?

Chalkboss

Same behavior here on my S4. A new sender fixed it, pucker factor defeated! I hope this is it for you.

edit, didn't read carefully. See below!

worf928

Given that you've already replaced the sender...

Remove pressure sender. Make an adapter for that hole that will allow connection to an external oil pressure gauge and test the pressure directly.

That will tell you on 'what side of the (new) sender' the problem lies.

Eplebnista

This:

Get a pressure tester like this
I have had cars where a bad resistor in the dash has caused ominous low oil pressure warnings when a mechanical gauge proved otherwise. The oil pressure pressure gauge in the 928 can get wonky for many reasons. Using a simple and more foolproof gauge is step one in the diagnosis of why your instrument panel is saying something.

V2Rocket

https://www.lindseyracing.com/LR/Parts/944OILADAPT.html

worf928

Ah! Nice. No muss, no fuss. Ordering presently (to replace the so-so adapter I made...)

worf928

Your local Autozone / Advanced Autoparts might have an external gauge for rent?

Crumpler

Gentlemen, thank you for following the thread.

I forgot to mention oil is Royal Purple 20-50.

I pulled out my log book, and sender was installed 2013 and looks like it was a cheapy -- unless VDO variants were cheaper then.

I used the links above to order kit and adapter, thanks again you guys.
Also ordered a VDO sender this time, I was reading in an old thread someone's opinion that anything but VDO was unreliable with limited performance life.
Man, would love it if it's something easy like that. Finger's crossed.

In the meantime I will get a better look at the harness and 14 pin connections. I'm sure there are issues there as well, I've been aware of that since my alternator upgrade.

Sean if you are following, can you put me in the que for one of your new units? I will call Roger in the morning.

And I found specs. for the sender in an old post by Dr. Edwards. Might be interesting to bench test the old bugger afterwards (the sender, not Rob...).

Best, Dave.

FredR

Dave,

If you really had zero oil pressure it would only take seconds before you knew about it well and truly. My VDO sender failed a couple of years ago and that one failed on the indication circuit but not on the alarm circuit. Replaced it with a stock VDO 3 pin unit and had all kinds of issues with it but it sort of worked. In the end I purchased a cheapo 2 pin item and for the time being it works a treat but if it falls over I will know where to suspect first. Golden rule- if instrumentation tells you something is wrong always check the instrument calibration first. That being said always wise to assume the instrumentation may be correct until you prove otherwise.
I also found on mine that several cores in the harness were complete toast and that included all three wires from the sender which made me wonder if a sender fault could somehow cause a high current flow that effectively trashed the sender cables. Either way, new cables and a new sender and it works fine at the moment- hopefully you have nothing more than this. If you look at the cables as they enter the 14 pin connector and flex the cables a bit you will probably find the insulation drops off assuming there is anything there to start with.

Crumpler

Ok silly question.
Got my gauge and adapter to read oil pressure. First problem is I don't have enough room to thread adapter and sender because of the oil pan.


My plan was to fabricate a plug for the bottom of adapter and leave the sender off while I run it to get direct readings.
Assuming I will get central warning with no sender but it shouldn't matter right? Has anyone else had this issue try to use adapter?

worf928

The adapter I made fits in-place of the sender so when used the 928 it's attached to will complain bitterly about oil pressure.

Crumpler

Got it, many thanks Dave.

I got a threaded plug for the bottom of the adapter, and, because I own a 928, I'm familiar with the art of JB-Weld

I will get some direct readings tomorrow and report back in.


Let me also add a little Sean harness ****...sweeeet.
Hoping I can just replace a sender and slap this mother on next, instead of a real low pressure rebuild.

SeanR

Couple things. Thanks a million for the harness order. Hope it's everything you expected.

I've had issues with the cheapo senders, some work, some worked for a few minutes, some never worked so I always use the more expensive one.

I'd not seen this thread until this morning and that adapter looks really nice. If you thread it all the way in the car, and then put the sensor in, do you think it would fit? That's one piece I don't have that I'm happy with. Being able to read the oil pressure while keeping the sensor would be awesome.