Rsingh7

Ok so I am having this weird problem, pulled a few wiring diagrams and am still lost.

1. Start the car..and my Oil Pressure Gauge shoots up PAST 5 and my oil light on the check system comes on. (However my oil level is fine and the pressure is fine, car runs excellent, sensor must be defective)

2. Found 2 connectors going to the Oil Gauge Sending unit... also found the 1.3 Bar Oil Pressure Switch/Sensor which is Gray/White located on the engine block.

Now, the wiring diagram says that Gray/white is 1.3Bar sensor, and the BLUE/Black Wire is the 0.3bar sensor.

However, the BLUE BLACK wire is connected to a connector that goes to the OIL PRESSURE GAUGE SENDING UNIT.

Question: 1} Where is the 0.3Bar oil sensor located on my 1991 audi 100? I can't seem to find it...is it BUILT into the OIL SENDING GAUGE UNIT?

2) I disconnect the blue/black wire from the oil pressure sending unit...start the car..the oil pressure gauges shoots up past 5 again at idle and driving, it doesn't move..HOWEVER the oil check light DOES NOT COME BACK ON...I reconnect the blue/black wire and the oil check light beeps and comes back on.

I am very lost in this wiring system. Anyone that can help me I appreciate it greatly.

I'm just confused if the low pressure oil sensor is somehow connected to the oil pressure gauge sending unit.

I think the culprit is my low pressure oil sensor but I can't seem to find it..I looked on the oil filter housing and can't find it..also I know for sure the high pressure is the one on the engine block since it has a white/gray wire going to it.


Does this car have 2 oil pressure sensors? I called the dealer and he told me it doesn't, but the wiring diagram shows it does...very confusing..

Anyway, any help on this problem will be appreciated greatly..thanks


1991 Audi 100 140K
1991 BMW 325i 92K
1988 BMW L6 142K
1985 BMW 735i 123K

Edd W

switch type sender.

I think that you have the feed wire for the gauge connected to the pressure switch, As soon as that switch closes with the oil pressure against it, it puts the return from the gauge straight to ground, hence the needle going right to the top of its range. That feed should go through a variable resistor in the sender to alter its resistance based upon the pressure it receives.

Find the wire that is going to the switch at the moment and swap it onto the gauge sender and swap the one that is on the sender at the moment onto the switch.

If there is another switch, that may be where the correct wire for the gauge is at the moment.

If you can find the correct wire for the gauge, I think you have it solved. The only other possibility for error is having the low and high pressure switch wires swapped (if it has the two switches).

Rsingh7

Thank you Eddy, I will try that!

jbofcg

Did this solve your problem? I have a 1991 Audi 100 that "clicks" in the start position and will not crank, while at the same time the oil pressure gauge pins at the top of the scale. Can a faulty oil pressure sender/sensor prevent the car from starting? The battery, starter and alternator are all fine.

Rusty Spokes

No..a faulty oil pressure sensor will not stop the car from starting.

A bad ground between the engine/transmission and the chassis will keep your car from starting and may explain the reason your oil pressure gauge pegs when you engage the starter.

All the voltage is trying to find a ground back to the chassis when you engage the starter (as the engine and transmission are mounted in rubber) and the closed electrical circuit on the oil pressure gauge is one of them.

I don't know what engine you have in a 1991..but look for a large ground strap..usually on the V6 above the alternator and bolted to the chassis.

Your local friendly auto parts store (FLAPS) will have a selection of ground straps..get one and add or replace yours.

jbofcg

Thanks Rusty. Mine is the 2.3 5-cylinder, normally aspirated. I will look for the ground strap you referenced, and other body grounds and clean them up. I did notice, when I was checking the trigger wire from the top of the engine to the starter, that it was cracked and brittle, especially where the wire bundle it was part of was held by the factory ties. It could be shorting there, I suppose.

jbofcg

You were correct, Rusty. I cleaned up every ground I could find, and the solenoid/starter connections as well. Started right up. Took it for a drive and everything was fine except for some muffled backfiring as I decelerated.
Could this be related to the battery being disconnected for a few days?

Rusty Spokes

Maybe..could be things in the OBC are out of wack and need some miles to reset..or could be some short fuel dumps in the intake via the cold start valve when you were trying to start the car and that excess fuel has to burn off..and again..you need to get the engine warm and drive around for a while.

Go out and enjoy for 20-30 miles and see?

jbofcg

[QUOTE=Rusty Spokes;24991681]Maybe..could be things in the OBC are out of wack and need some miles to reset..or could be some short fuel dumps in the intake via the cold start valve when you were trying to start the car and that excess fuel has to burn off..and again..you need to get the engine warm and drive around for a while.

Go out and enjoy for 20-30 miles or so.

I went for a test drive and still had the backfire issue, and what appeared to be a "rich" fuel mix condition. It stumbled and killed at a stop sign. Limped it home and opened the hood. I saw that the boot over the connector to the fuel pressure regulator was moved. I reattached the connector and my "rich" condition was resolved. I must have jarred it while finding and cleaning the chassis and drive train ground connections. All is well.