Oil Pressure Gauge Swings

[swirvin]

I just purchased a 1986 Porsche 944 (with the VDO instrument panel) and took it out for a spin for about an hour. When starting out the oil pressure gauge was steady between 3 and 4. While driving to the highway there were a few red lights I had to stop at and everything was fine, the car shifted smooth with no problems. After driving about 30 minutes straight I had to stop at a light and noticed the oil pressure needle was swinging between 0 and 5 (It does not do that while driving, only when stopped). Any idea what could be causing this or what I should look at to try and troubleshoot the problem?
Not sure if this is related but while the oil pressure gauge is swing the car bucks wildly when I start to accelerate in first gear. I have to start with the engine rev'd at high RPMs to get it to not buck as much.

Where do I start troubleshooting?

-= Irv =-

[Grandad#3]

Hi swirvin, The below link shows how to test the gages. As in anything electrical on these cars it is best to find and clean all ground points. The main Ground is located on the Bell Housing. Put some tape over the Clutch Inspection Hole before you remove the nut and washer on the ground cable. You don't want anything falling down in the hole.

Sensors and Gauges - Information, Troubleshooting, and Testing

Cheers,
Larry

[ernie9944]

[QUOTE=Grandad#3;5558252]Hi swirvin, The below link shows how to test the gages. As in anything electrical on these cars it is best to find and clean all ground points. The main Ground is located on the Bell Housing. Put some tape over the Clutch Inspection Hole before you remove the nut and washer on the ground cable. You don't want anything falling down in the hole.



yup Larry is rigth

[John_AZ]

Step 1--easy
On the oil pressure sender on the oil cooler housing, carefully tighten the nuts. NOTE these posts are hollow and brittle----ie, they break easy---be careful

Then follow the wires up over the WP (water pump) and check for bad installation, cracks in the wires or missing wire seathing.

Step 2.
Put 2 new "O"rings in the OPRV (Oil Pressure Relief Valve)





Clean the OPRV parts carefully. Get a new crush washer or it will drip

Step 3

Get a new oil pressure sender. Mine stopped the low rpm jumping with a new sender.

GL
John

[racer]

As another well respected resource, spend some time on Clark's Garage Home Page

Generally speaking, under use, oil pressure should be 4-5. At idle, 3 is common. Less than 3 is "ok" under extremely hot conditions (oil thins out at extreme heat) but not ideal. Less? usually trouble.

Sounds like an electrical issue. Clean off grounds first.

[swirvin]

Thanks for all the good information. I didn't expect the quality of the replies I got.
Here's an update to my original post...I'm not sure what I was seeing the first time I took the car out but here's what's actually happening, when driving the oil pressure gauge does not swing, it reads pretty steady on the high side of 4. When I an stopped the gauge starts to swing between 0 and 2. Is this normal?
Also, the bucking in first gear I mentioned was all me. I wasn't giving the car enough gas when starting in first gear. Unlike my Jetta I have to give this car significantly more gas to get it going.

-= Irv =-

[ernie9944]

Originally Posted by swirvin

Thanks for all the good information. I didn't expect the quality of the replies I got.
Here's an update to my original post...I'm not sure what I was seeing the first time I took the car out but here's what's actually happening, when driving the oil pressure gauge does not swing, it reads pretty steady on the high side of 4. When I an stopped the gauge starts to swing between 0 and 2. Is this normal?


-= Irv =-

A car in healthy condition should read as this ---on start up pressure between 4 & 5 bars-----while cruising around will vary between 5 & 3 bars depending on shifting & rpm-----once at operating temps with the gauge between ½ or 3/4 oil pressure should be no lower then 2 bar the gauge swinging between 0 & 2 is not normal. on start up idling at 950 rpm between 4&5 bars holding it at 1100 rpm oil pressure is between 3&4 bars At idle after a very hard run a little over 2 bars

[John_AZ]

ernie,

I doubted you ever took your 968 on the road.

The car is always immaculate.

I see from the odometer the trip went from 80013 km to 81097km.

Felt great I bet....

John

[ernie9944]

^^No never took it out on the road ,1,084 km of driveway runs will get under your skin after a while believe me.As far as the car being immaculate it will always be if I can help it,my ex 944 is the living proof of how well a car can be taken care off, even after 26 yrs of ownership it look brand new even thought I will sometime take it on small 2,000k miles spins .

[bobbybarnett]

Swirvin: I am seeing the same thing as you. At cruise, my oil pressure is stable at 4+ bars. At idle, it jitters around 2, and if I step up the RPM to 1200 or 1500, the pressure jitters around 3 or so (but not as much jittering). Overall, I'm happy with the "average" level of oil pressure, but REALLY don't like this jittering thing.

Have you solved your issue? Was it this ground? the sender terminals? the sender itself? Do you have any other thoughts?

[bobbybarnett]

FWIW, I just swapped out my sender with a new one from Pelican - and the needle is as steady as a rock - as it should be. My oil pressure is also reading almost a half bar higher than it used to. Perhaps the failure mechanism in the old sender also changed the pressure/resistance curve used to drive the gauge.

Anyway, I was a bit worried about actual oil pressure issues - and now I'm doing the happy dance.

[jsb944]

The pressure gage on my S2 used to bounce like that.....changed out the sender and it's rock solid...like ernie's.

[John_AZ]

Originally Posted by John_AZ

Step 3
Get a new oil pressure sender. Mine stopped the low rpm jumping with a new sender. GL John

Originally Posted by bobbybarnett

FWIW, I just swapped out my sender with a new one from Pelican - and the needle is as steady as a rock - as it should be. My oil pressure is also reading almost a half bar higher than it used to. Perhaps the failure mechanism in the old sender also changed the pressure/resistance curve used to drive the gauge.

Anyway, I was a bit worried about actual oil pressure issues - and now I'm doing the happy dance.

Originally Posted by jsb944

The pressure gage on my S2 used to bounce like that.....changed out the sender and it's rock solid...like ernie's.

My My My x3 +++ Worth a try.