Low oil pressure

[massive]

Was driving my 84 944 today and noticed the oil light flicker briefly when I stopped at some traffic lights, looked at the pressure gauge and it was reading 0.5-1.5 with the car idling at about 500 rpm. If I increased the revs the gauge went up.

I then drove the car, oil pressure increased to about 3.5 - 4.0 (I'm sure it used to read around 4.5-5.0). I noticed when shifting that the pressure would drop to near zero.

Any ideas what I should be checking, was too dark and wet to inspect this evening, hopefully be able to take a look in the morning.

I replaced the OPRV for a new one about two years ago, so hopefully it's not that.

Any help appreciated, thanks

[9FF]

It's normally an electrical issue. Check the connections are tight on the oil pressure sender, not loose, next check your alternator voltage at the battery with the car at idle, good voltage, next clean your grounds, still there, next swap out the oil pressure sender, not cured, start looking for mechanical oil pressure issues.

Your readings are not far off from normal, so I suspect an electrical problem if this suddenly happened.

[zedsn]

Check the oil level and if ok could be rod bearings.

[holtzy822]

My 87 was having the same symptoms, we did a full oil change and replaced the oil pressure sensor and we haven't had any problems since, 500 rpm seems aweful low for idle though... Mine idles at 950 rpm

[preludeofwrath]

sounds about right. in traffic mine dips as low as 1.5, and i read that it can go down to even 1 bar at times. and it is most certainly one of the many twitchy needles in the cluster

[sausagehacker]

The oil pressure sender unit is a poor design and goes out a lot. I remember reading a writeup of someone who took one apart, and it's a very crude potentiometer.

I've heard that the Uro brand sender is trash, and will go bad in months.

[massive]

Originally Posted by holtzy822

My 87 was having the same symptoms, we did a full oil change and replaced the oil pressure sensor and we haven't had any problems since, 500 rpm seems aweful low for idle though... Mine idles at 950 rpm

What should the rpm be normally at idle? I know the throttle body was cleaned recently because the car failed Uk emissions test during the MOT so I wonder if they also adjusted the idle screw too?

[CHICKS]

When was the last time rod bearings were done? How many miles? What weight oil do you use? Your location, and outside temp?

[mytrplseven]

There's a write-up on Clark's Garage on re-adjusting the idle that involves a jumper on the diagnostic plug. When finished, you should be looking at an idle of around 900 rpm. You'll be adjusting things on the throttle body to get the final reading. It's pretty simple.

[massive]

Originally Posted by CHICKS

When was the last time rod bearings were done? How many miles? What weight oil do you use? Your location, and outside temp?

Rod bearings, not since I've had it. Currently at 137, 000 miles (I bought it at 117, 000). Location UK, mid-winter about 5°c and very wet currently. Not sure what weight oil but it was changed in November by a specialist porsche workshop so should be the correct type.

Sent from my GT-I9300 using Tapatalk

[massive]

UPDATE:

Checked oil level, all is okay, plus no noticeable oil leaks from under car.

I then went to start the car, could hear the starter motor turning over but engine wouldn't fire. I then had a poke around the relay board and found that if I put some pressure on the DME relay then car would start (can hear the relay ticking madly inside). Removed pressure from the relay and car dies.

Whilst the car is idling from cold the pressure gauge reads 4.5-5.0 (whilst putting pressure on the DME relay).

Could a dodgy DME relay be related to the oil pressure thing? Or is it just a coincidence?

[massive]

UPDATE 2:

Installed new DME relay from Porsche (£60), car now starts first time.

Took her out for a fairly decent run on local roads, once up to temperature oil pressure is showing about 3.5 under normal driving conditions, at idle needle was reading approx 1. Engine idle speed was still 600 rpm.

Have now backed out the idle screw so that she idles at 800 rpm. Need to do another test run.

I also bought the oil sender unit in case it's still needed, can someone tell me if the install is a messy job? If I remove the old one am I gonna need an oil pan to catch a load of oil?

[sausagehacker]

The goal is to pull it out and quickly pop in the new one. You'll need to drop PS pump if I recall correctly, and use a 24mm pump wrench. Harbor freight sell a full metric set for $50.

IMO it's best to do it during an oil change, so there's no rush.

Another tip: if you get the wires switched, the gauge will always be pegged. Try switching the wires if that happens.

[massive]

Originally Posted by sausagehacker

The goal is to pull it out and quickly pop in the new one. You'll need to drop PS pump if I recall correctly, and use a 24mm pump wrench. Harbor freight sell a full metric set for $50.

IMO it's best to do it during an oil change, so there's no rush.

Another tip: if you get the wires switched, the gauge will always be pegged. Try switching the wires if that happens.

Thanks for the tip

[massive]

UPDATE 3: Did a test run with idle set at 800 rpm and all oil pressure readings seem to be back to normal for now.