StratfordShark

I've just installed a new oil pressure 928.606.203.05

I've replaced the original connector with three individual bullet connector which fit firmly to the sender pins, and for protection I've found rubber boots for satellite co-ax connections fit firmly over the detents at base of pins.

The MY91 wiring diagram shows these connections to the sender:
Brown/Red - M (ground)
Blue/Black - WK (warning contact)
Blue/White - G (sensor)

On my car the only matching wire is Brown/Red, the other two are Green, and Green/Black. So I've connected them:
Brown/Red - M (ground)
Green/Black - WK (warning contact)
Green - G (sensor)

I'm puzzled about the different wiring colours, but also puzzled by behaviour of the gauge on testing. When I start the engine the oil pressure warning light goes out, but the gauge only moves up to about 3 bar. It's around 20C here, but I'm pretty sure even in warm weather the idle pressure always moves to 5 bar from cold, and moves down to around 3 bar when car fully warmed up. Much above idle and before I changed the sensor the gauge would move smartly to 5 bar.

I'm using VR1 20W/50, and the only other thing that's changed since removing the original sensor (which I think had a slight leak) is that I installed a brand new engine ground cable.

Do you think there's a problem with the sensor (it's NOS, dated Oct 2009), or could I have got the wiring wrong? I attached Green/Black to the WK warning contact pin as it was closest match to Blue/Black on the wiring diagram.

Thanks for any help with this double puzzle!

StratfordShark

Done a bit more testing. Tracing wiring back to 14 pin connector, my pin attachments are correct. I think the wiring diagram just made a mistake not changing colour from the pod side of the 14 pin connector to the sender (the diagram shows the ground wire correctly changing from brown/green to brown/red at sender, but colour of other wires same either side of 14 pin connector whereas they change.

Next I tested resistance of the sensor itself With engine off it measures 5 ohm between the sensor and ground (G and M) pins. After starting from cold, it measures 96 ohm.

I found a data sheet for the sensor which states resistance range is 10 ohm to 184 ohm, so it's possible my 3 bar reading at cold idle is a faulty sensor. I bought it as NOS and it's in Porsche box, but if the data sheet is correct my readings definitely low. It's a shame as I wanted to button things up and drive her!

Has anyone tested recorded resistance of their 928.606.203.05 sensor? Oh and PET shows that the sensor with 03 at the end and the 05 both OK for 87-91 and 92-95 cars so I'm not sure what changed.

FredR

Adrian,

When I had a problem with my original sender I purchased a new item from Roger and gave it to the local agents to fix it as I did not have the time or inclination to fix things in those days about 8 years ago. Upon getting the car back i was most unhappy with the results as the dash readings were twitchy and oil pressure indicated seemed lower than I normally expect from the engine. Eventually I got round to some inspection and was horrified by what I found- the cables they had hooked the sender up to in the engine harness were in a disgraceful condition. I then decided to rip the harness out and build one myself. Upon completion I found the display was no better so threw in the towel, purchased the earlier two pin sender and "voila" the readings returned to what I expect [much to my relief]. I figured there must have been a problem with earth connection [the third wire]. Still have a nearly new 3 pin sender sat in my garage gathering dust somewhere. This is why if one wants an accurate reading Porsche recommends use of a calibrated Bourdon gauge as these electrical gauges can be quite a way off.

As to the wiring discrepancy all I can say is it would not the first error noted in the wiring diagrams!

StratfordShark

Thanks Fred. The wiring is in excellent condition having stripped it back an inch from the original connector (oil had softened the wires at base of connector, so this project worthwhile just for restoring good wiring).

Otherwise the readings are not twitchy, just low in an unsatisfactory way since when the car is hot seeing the indicated pressure drop at idle but go full scale on revs is reassuring.

I'll leave the new connector hooked up for now, but probably bite the bullet and source replacement 3 pin and see if it's showing different resistances. Interesting you were seeing low readings too with a new three pin sender so maybe it's pot luck getting one to read correctly.

FredR

My perception is that the problem lies with the way the system reads the signal and that somehow there was a problem with the system resistance between the 14 pin plug and the gauge in the dash panel- i,e, something I could not be bothered to chase out. Maybe it was a false earth earth of some kind.

If it is of any value I may be able to dig out the redundant 3 pin sensor and jury rig a test to measure the resistance with pressure if it helps at all- maybe someone has those values?

StratfordShark

Oil pressure was reading fine in past, it was just that the sender looked as if was leaking oil (not certain — it may have dropped onto wiring from above).

Yes please it would be great if you could find your sensor. Just the resistance with no pressure input would be useful between the G and M pins. If you make up a rig and check the 5 bar resistance even better! I've found a pressure resistance set from the two pin sensor which shows indicated 2 bar at 95 ohm, which is close to what I'm seeing indicated and measuring when it should be around 185 ohm and showing 5 bar. In short my new sensor is showing too low resistance.

928NOOBIE

FYI I had the oil pressure sender replaced on my car it's doing the exact same thing....at idle or running when it should be on 5 it's about 4 or 4.5....mine appears to be reading between 1/2 and 1 bar low. Glad to see it isn't just me.

I replaced my sender because when things got hot (like on a hot summer day hot) it got sluggish and would sometimes read so low the oil light would come on and then slowly it would go up...I knew actual pressure was fine....sender just wouldn't work right when it got past a certain temp.

Maybe I need to change the sensor out ...I swear I thought it was the 2 wire one I bought. The new one reads nice and smooth...just a little low....

I read this thread but need to take another look underneath and see what I really have....maybe my sensor is just faulty...

StratfordShark

I think the 3 pin sensor came in with S4 1987 on, so you would have the 2 pin.

FredR

3 pin came in with 89 model

ROG100

1989

ROG100

In my long experience with oil pressure sensors I have found the light to be accurate whereas the gauge needle can fluctuate. On earlier cars the needle can sag giving lower readings.

StratfordShark

Of course digidash - daft of me not to think of that. Thanks Roger.

FredR

Adrian,

Had a rummage in the garage this afternoon and whereas I found the defunct sensor I could not find the relatively new 3 pin sender. I know i put it away somewhere but...? Unfortunately we are in the middle of "silly season" here and the humidity is through the roof at the moment -20 minutes of shifting my storage boxes around was about as much as I could handle soaked to the skin in sweat.

All being well I will have another rummage tomorrow.

StratfordShark

Thanks very much for looking Fred, but please wait till conditions are vaguely comfortable in your part of the world!

FredR

Just not in my nature to give up! Had another rummage- it was a bit milder than yesterday but still end up as wet as when I go for a shower-

Unfortunately I could not find the sender I was looking for and boy does that annoy me- grrrh!

There must be at least one kind soul in our community who has a three pin sender squatting in his parts bin who can at least measure the static resistance for you?

Perhaps this evening before I go for a shower I can [with the the garage door closed] attack the problem stripped down to the "bare essentials" and then straight into the shower!!!

I have some 10 storage bins and two sets of shelves plus a work bend littered with tools, spare parts, cleaners, lubes etc etc. For sure when the cooler season returns end of October I will have a good tidy up and sort out.