Oil pressure senderunit removal '90 S4
 

Hi!

My oilpressure indicator is not working properly (pinned most of the time, even when car not started) and I pretty sure its the senderunit that is the problem so I have bought a new one to replace it with.

But I got into a problem right away and that is that I cant get the cable of from the old unit. i have the 3pin senderunit type and a 928 S4 -90.

Is there a locking mechanism on the connector or is it just to pull it?
I havent used anything else then just my hand to pull on it but enough to think that I´m not doing it right.

Also will it drain much oil to remove the entire assembly?

Thanx!

The cable connector is a bit of a sod to get off the three pin senders- just be warned that they are no longer available and thus to my knowledge cannot be replaced with a stock item if damaged during removal [ask me how I know!]. Others may have some good tips for doing this given it is a bit awkward to get at.

You may also find that the sender is not the problem if you are assuming such without diagnostic analysis. if you have not done so already take a look at the wiring entering the 14 pin connector next to the hot post in the engine bay. chances are the cables entering from the engine side [including the three from the sender] are toast by now. You may find the insulation is crumbling off or even non existent which does all kind of weird and wonderful things to the output signal.

As I am aware removing the sender does not liberate much oil but there will be a small fugitive loss.

Rgds

Fred

Attachment 1075960This is what happens if the connector doesn't come off. I ended up replacing the sender. I did drain the oil first. Good luck

Ok, thank you Fred for your answer.
I will check the connector and look for any signs of the problem there. The reason that I think its the sender unit is that it seems to work for some pressurereadings and then when the pressure is outside that window it gets pinned at max. It usually works when the engine is cold because the window is around 5bar and then it gets pegged when the engine is getting hotter except for when I have a RPM that makes the pressure go up to 5bar again.
I think I have read a thread before that stated the exact same problem and then it was the senderunit and thats why I ordered it.
But as you say, electronics can sometimes act up pretty strange when insulation gets chipped of so it might be the cables after all.

Hi David, funny I am also a new guy here and also picked this as my first job to do.
It is alot easier if you remove the oil filter first and I found the best way was to get a small screw driver in between the sender unit and the plug, you can slowly apply some pressure form all sides of the unit and finally used a set of multigrips to wiggle the plug off. It took me a bit of time but eventually it came off - it must have a fair bit of a grip as it is rubber and has 3 pins to grab with.
As Fred said though it was actually the wires and the insulation with mine that was damaged and I still haven't found a great solution to fix that - just got some shrink wrap and tried to seal it as best as possible.
The more experienced guys might want to chip in here as it might actually be the earth connections on the back of your gauges that are causing the problem.
Hope this helps - I am keen to make a contribution here as there is so much information and people that have helped me.
Simon

Hi! I thought of just that solution to get it out. I last tried to do it at the same time as I did oilchange last and then i had the filter out so I´ll have to look at it now if its doable without it. but I will check the cables first but I didnt apply much force at all as I thought I might do it wrong and didnt want to break anything. When I look at the new senderunit it seemed possible that there is a locking mechanism in the connector and thats why i didnt pull it hard that time.
My thoughts has also been in the connector itself because of its position the problem could be in there where the cables enter the connector or in the internal fittings. Might even be moisture prehaps in it but atleast my problem does not seem to be weather-related at all.

That's exactly what happened to me as I went through a big storm and due to the location of the plug it must have been soaked with water and the gauge started to jump all over the place (my first 928 lesson - I stopped straight away and realized the insulation was coming off the wires, a bit of electrical tape and the problem stopped - I decided to replace the sender unit anyway).
Just takes a bit of force getting the plug back on takes a bit of pressure as well.

As I think of it more i have already had a moistrelated problem with my 928 that I solved by cleaning the earthcable to the engine. The problem then was that the idle could wobble when the car was cold and sometimes it could fail to pick up the rpm when going to idle and die.
The reason I got that problem was that the first year in our new house i had the car in the garage over winter but it go really damp in there and that left some visible oxidation on boltheads and other details in the enginebay that wasnt there before. And this idle-problem too.
The oil-pressure issue is a later one but maybe it has its beginning the same winter (not sure cause the car hasnt been used more then a couple of 100miles/year the last 5 years)

After that winter I purchased an inflatable car tent that i keep the car in over winter to protect it from the environment and that have worked really well.

https://cimg4.ibsrv.net/gimg/rennlis...38d7bdf2ac.jpg

928 in a bubble

I live in Sweden and in the winter we often have big temperature-changes and that is what is causing the moisture problems in my garage (not insulated)
We can have temperatures down to -27F and a meter snow and then a couple of weeks later it can be +50F and all the snow turned to water.

Getting the connector warm (very) will allow it to be removed with less force.

I fell into the trap of thinking the problem was with the sender unit after having some display issues. Gave the new sender to the main dealers and asked them to fit it for me as they were doing something else for me already.

When I got the car back the display worked [sort of] but it was erratic. It was then that I looked into what they did and was concerned when I saw that they had simply cut the three wires close to the sender and then used red crimp connectors crimped at the wire end and stuffed over the pins at the other. To be fair it sort of worked but they should have covered it with heat shrink but given we do not have much rain here and when it does last thing I would do is drive the 928 it was not really an issue.

However when I checked the rest of the wiring it was a complete dogs' breakfast from the 14 point connector back to the engine. Some cores had no insulation, others it fell off if you looked at it!
In the end as I could not get the correct colour cores here, I made a sub harness to carry the 3 wires to the sender, the wire to the a/c solenoid, voltage from the alternator and the wire to the level sender and it works reasonably well. Good cables of any colour are far better than old cables with the insulation no longer present or working.

For the power cables I kept the sleeving in the alternator area and for all I know they may be in a bad condition underneath [a known failure spot] but where they emanate from under the cam cover I wrapped the cores with high temp self vulcanising tape and then ran the 16mm red cable and 4mm yellow cable in a flexible conduit.

Rgds

Fred

Before I change the sender unit I will go thru the cables much more after your experience. I might not be able to return it but well its atleast better than changing it and have the problem left.

Just to be clear the indicator shouldnt be pegged with the ignition on and the engine off right? (Just to be certain)
This is the case with mine and that might make it easier for me to see if I have found the faulty wiring or insulation without having to have the car warm and running.

The needle can do strange things when there is an electrical fault.

Mine still pegs occasionally at full scale deflection when I shut off the engine. You can see the oil pressure drop as the engine stops and then it suddenly swings over to full scale. I cannot find the reason for this- probably something to do with earthing or the lack of it. Posted about this previously but no solutions proffered.

Rgds

Fred

That sounds like my problem. At first the readable scale was much wider for it and it culd show pressures down to 4bar and then it got pegged. I will take a look at the connector this afternoon and see if there is anything obvious.

Ok so now I have done some fast diagnostics (Without lifting or starting the car) but with some interesting results.

Unlocking the car the needle is at 0 pressure. I open the hood and look at the connector and cables visible at the passenger side. It does not look damaged or any signs of that the insulation is coming of.

I disconnect the connector and look at the connectorpins and they do not look oxidised (maybe not a word..) I clean them anyway with oxideclean spray and connect it again.

Then I go in the car and put the key in and turn on the ignition. The oilpressure gauge gets pinned straight away (I´m not starting the car)
The car now also show the voltage and fuellevel + temperature.

I turn of the ignition and removes the key. All gauges go back to zero except the oilpressure.

I then go and disconnect the 14-pin connector and the gauge is still pinned...

I connect it again (still no change) and its not until I lock the car and the mileage dissapear from the dash that the gauge drops to zero again.

I´m now thinking that this is an electrical issue somewhere from the connector to the (or in) dash.

What do you think?

Sounds like you have a issue between the jump post and gauge needle. Time for you to break out the wiring diagrams and multimeter.