OIL PRESSURE SENSOR: Mechanic Stumped - Scandal!

Hi everyone, a NEW person is greeting the community of DIY enthusiasts .

Let's get to the point:
My engine is a 6-cylinder Ford engine, series 2725, with a displacement of 5.9 liters and a power output of 94 kW, manufactured in 1989.
Here, the oil pressure indicator has now failed . It consists of a moving-coil pointer instrument and a DUO sensor, both from VDO.

The error:

Both instruments go to the rightmost position when the ignition is turned on !

The following has been checked.

Disconnect the sensor cable from the indicator instrument: right-hand side.
Bridge between terminal G and minus: Left stop.
Technician's diagnosis - Display OK.

Resistance measurement at the donor: Terminal G to ground = no reading, should be approximately 10 ohms.
Diagnosis: Sensor defective.

Resistance measurement of the connection cables: 4 Ohms = OK.

Ordered a new sensor from VDO in Hamburg. Installation - the same error.
Another donor has been ordered, and the donor's resistance was measured on-site without installation = no reading.

The technician is at a loss. The boss also doesn't know what to do !
Now I'm in this situation and I look quite foolish, something like !

The company I hired has been delaying things for weeks.

I also tinker with my engine myself, doing the usual stuff.
Therefore, I have...
Now, I'm hoping that someone among you might be familiar with VDO instruments and be able to offer some advice.
It really shouldn't be the case that the old regulator and the two new regulators have the same problem, uhmmm, or does it?

Best regards from the Weser river - Peter.

Quote:

Resistance measurement of the connecting cables: 4 Ohms = OK.

That's way too much; you would need quite a few meters of thin cable for that.
If your measuring device is working correctly, it should display a value significantly below 1 Ohm.

I once had a similar issue with the temperature gauge on my Wartburg 353. It turned out to be a grounding problem.

In my opinion, the cable resistance is far too high. Unless the measuring device is a piece of junk from Billigsdorfer & Partner, which randomly outputs measurements.

Hello, and what should I do next?
Are there any auto electricians among you?
I am interested in the principle of operation of pressure measurement.
Okay, so: 12V is applied to a fixed resistor in the display, and then through a coil winding to the sensor – in this case, via a sliding contact of a variable resistor to ground.
Consideration wrong or right?

Best regards, Peter.

Hello,

Normally, the sensor uses the engine block/cylinder head as a ground (I assume the sensor is located in the cylinder head), so it's possible that the engine/cylinder head is no longer connected to the vehicle's ground. Simply try connecting a cable from the negative terminal of the battery to the cylinder head/engine block, and it should work.

Hi everyone,

Quote:

Resistance measurement of the connection cables: 4 Ohms = OK.

I will check that again .

Thomas K.: The sender is located just above the oil pan.

The question about the sender that I mentioned earlier is still bothering me: If, on the extended sender, the resistance between terminal G and the housing (which is motor ground) is infinite.
How is the electricity supposed to get to the motor that moves the pointer at the top?

But all the donors have the same defect .

Best regards to everyone, from Peter.

Sure that your sensor is the correct one and not just a pressure switch? Have you checked the sensor for proper function?

Hello Rainer,
The old one and the new one look like twins; there are no differences. The part number is also identical!

Best regards, Peter.

ps-skipper wrote:

The question about the sender that I mentioned earlier is still bothering me: If, on the extended sender, the resistance between terminal G and the housing (which is motor ground) is infinite - How is the electricity supposed to flow to power the mechanism that moves the pointer at the top?

Counter question...

bei ausgebautem Geber ist der gemessene Druck doch Null. Or what?
What reading do you expect to see on your oil pressure gauge? Normally, it should be at the left-hand limit. So, the current flowing through the gauge should also be approximately 0. Therefore, the sender is highly resistant!
What is wrong with your measurement that you cited earlier?



Tonight, I'm going to measure my sensor, and then I can give you more details.

Hello Bertil,

The initial value should be 10 ohms, and the final value should be approximately 180 ohms.
I obtained this information from the non-fiction book 'Diesel Engines: Maintenance and Repair' by Hans Donat, published by Klasing Verlag.
Ich wollte eine Kopie davon posten , geht aber nicht in diesem Forum. Too bad.
If you disconnect the sensor cable from the sensor while the sensor is functioning correctly, the instrument will go to the maximum reading (right stop) when the ignition is turned on. With the ignition off, it will go to the minimum reading (left stop). Reconnecting the sensor cable, turning on the ignition, and the pointer will move slightly away from the maximum reading towards the starting position. As the pressure increases after starting the engine, the resistance in the sensor increases, and the pointer will move accordingly.
That's what the book says, but it's not like that for me.

Best regards from Peter.

Hi Peter,

ps-skipper wrote:

Hello Bertil, The initial value should be 10 ohms, and the final value should be approximately 180 ohms. I got this note from the non-fiction book: "Diesel Engines: Maintenance and Repair" by Hans Donat, published by Klasing Verlag.

My Alzheimer's isn't that advanced yet, and the textbook is full of nonsense!

No oil pressure: extremely high resistance (over 5 megaohms), and at 5 bar of oil pressure, it's approximately 140 ohms.

My sender, however, is a very old VDO sender without a warning light, which is connected at the top with a T-piece (see picture) ... and the VW 827 engine is anything but a diesel.

Hi Bertil,
It actually works with pictures, where is the button hidden?
I found a website that might be helpful.
http://home.arcor.de/ohf-archiv/ohf_archiv/Motor/Anbauteile/Oeldruckgeber/oeldruckgeber.html
I will get back to you again tonight .
Best regards,
Peter.

Bertil, take a look at the thread .

ps-skipper wrote:

Hi Bertil, It actually works with pictures, where is the button hidden?

With a few more stars next to your name, it will also be possible (only for "professional mechanics").

@ps-skipper

Have you tried connecting a wire from the engine block to the negative terminal of the battery to ground it, and then trying it? I think your problem might be caused by a bad ground connection on the engine.

I can't imagine that VDO sensors are defective from the factory, and that this happens repeatedly.

If necessary, try connecting the oil pressure gauge to the open air using an external wire; you'll likely find the solution quickly that way.

Hi Thomas,

ich habe per Zufall einen Thread gefunden , der wie Faust auf Auge passt. Die Adresse ist zwei Postings höher in meiner Antwort an Bertil. Die Klick doch bitte mal an . Vielleicht sehen wir dann weiter . Liebe Güße v. Peter.

Bertil, could you also take a look, please?


Have you tried connecting a wire from the motor block to the negative terminal of the battery to ground it and then trying it? I think your problem is caused by a bad ground connection on the motor.

But would the starter motor then turn, and would the alternator run? Both housings are connected to the engine ground . Peter.

Hello ps-skipper,

Yes, I looked at the link, but I'm still having trouble believing that there are three sensors, two of which are brand new. Therefore, I don't think it's a faulty sensor.

For me, the readings I'm getting in the workshop are evidence that there's a problem with the grounding, because when I connect G to ground, the instrument shows a full-scale deflection to the left, which is correct.

It's not that difficult. Just connect a wire from the battery's negative terminal to the motor or the motor's housing to see if it starts working again. You can do this while the engine is stationary or running.

Okay, so instead of continuing to speculate and philosophize, just do it.