PAULSPEED

My friend is having a problem with a 1997 993.
Here is what is wrong.

The problem with the car is when you turn on the ignition (engine off) the oil pressure gauge goes to max pressure. We know it is not the sender because we disconnected both wires and still the same problem. We also know that it is not the gauge, tried another and the same problem. So most likely it is a grounded wire somewhere between the gauge and the sender. I also disconnected all wires to the engine so the short is not on the engine. Most German cars usually have the same kinds of problems so if someone else has had this the short may be in the same place. Thanks in advance for any help.

Thank you for any reply.

Paul

IXLR8

You might have an open, not a short.

The gauge reads high as the resistance goes high.

Measure back from the instrument panel back to the pressure sensor. With the engine off, you should measure about 10 ohms. If you read in the hundreds, there is your problem.

nile13

What does the gauge do when the car is running?

PAULSPEED

My friend says the gauge reads high with the car running.

Paul

nile13

The usual failure mode of the sender is low reading and light coming on. I would check oil level first. Than check continuity between connectors on sender unit and connectors behind the dash.

IXLR8

You had the gauge out. Take a DMM measurement at the Green/Red wire and vary the engine RPMs from idle to 2500 RPM. It should vary between 10 and 184 ohms, give or take.



If the meter reads open circuit, your sensor is open internally or there is a break in the wire or connector.

PAULSPEED

Thank you for the graph.

Paul

PAULSPEED

Thank you very much for your response.

Yes it was an open wire from the sender unit.

Now the sender unit needs to be replaced. My friend
says that the motor needs to be removed. A shop down the street
has a fabricated tool to do the job but it still takes about
three hours to replace the sender.

Has anyone ever drilled a hole saw into their car to
replace the sender unit.

Any help would be great.

Yes we have the instructions to remove the motor. It sounds like the throttle cable can be a big hang up.

Paul

nile13

Engine does not need to be removed. Removing intake manifold would help and give plenty of space to reach and replace the sender unit.

A shop charges about 3 hours, yes.

geolab

If you want to DIY, you could fabricate the tool as well for 5 bucks
Its nothing but a reversed spark-plug puller
let me know if you are going to DIY.
If so, will type a write-up for you, but not for the shop


myth

IXLR8

Paul, by "open wire" do you mean you measured back from the dash and the circuit was "open" not knowing if it is the wire or sender unit.

Just wondering why the sender unit needs to be replaced if it is an open wire.

BTW, location-wise, the oil pressure sender is located top, slightly left of center in this pic...two wires going to it.

PAULSPEED

Just a picture of the fabricated tool would be great.

Paul

PAULSPEED

My friend bought a oil sender for over $140 his costs.

He is going to lift the car and then drop the motor a little.

He then wants to get his hands up on top of the motor to
remove the oil sender.

He has removed the air plenums but there is some oil
condenser box in his way that he needs to get to the oil sender the other way.

Thanks for all you replies.

Paul

L23FPorsche

I'm very frustrated that I still have a gauge issue after replacing the sender with the more expensive VDO unit. I did check the ohm reading at the harness and found that there is no open circuit there. I'll be checking my ohm reading at the gauge tonight. At some point the gauge faces where removed for a color changed and then changed back. I have read that this can cause a problem? Also what is the "Central Informer"? This is where the green/white wire goes. Does it have any bearing on the gauge reading?

IXLR8

I do not think so.

The Green/White wire is from the oil pressure switch and activates the idiot light in your instruments.

The Green/Red wire from the oil pressure sensor is for the gauge.

Both the sensor and the switch are in the same device.