VDO pressure sensor wiring

[Ponk]

Hi chaps,

I think i've got this sussed from the DTA wiring diagram but I wanted to double check.

I've got a 0-10 bar VDO pressure sensor that I plan to use for fuel pressure. It's got two terminals because it's intended to be an oil pressure sensor with an additional terminal for a low pressure warning light.

The "WK" terminal appears to be for the warning light. "G" i'm assuming is the signal wire (Pin 33 in my case for an S40 ecu). Then i'll need to splice in the 5v signal feed with a 560 ohm pick up resistor (Any idea where to get one of these?). Lastly the sensor will be earthed through the NPT thread in between the sensor and the adapter.
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[mefmotorsport]

OK, you've got the wrong sensor really, the one that DTA recommends has 2 terminals, the resistor of the sensor goes between the terminals and is isolated from earth. the sort you have has a switch to earth on one terminal and the sender to earth on the other. It's not ideal as you'll be tying the DTA sensor ground directly to the engine so you could suffer with introducing interference signals up the ground wires. Also have you checked the sensor resistance, it should be around 10 ohms with no pressure and go up to 100 and something with 10bar. If your's has a different resistance then you'll need a different resistor or will have to write a new calibration table. You will get a 560 ohm resistor from maplins or somewhere similar. I put my resistors at the ecu connector end to save the extra wire to the sensor!

Martin

[Ponk]

OK, you've got the wrong sensor really, the one that DTA recommends has 2 terminals, the resistor of the sensor goes between the terminals and is isolated from earth. the sort you have has a switch to earth on one terminal and the sender to earth on the other. It's not ideal as you'll be tying the DTA sensor ground directly to the engine so you could suffer with introducing interference signals up the ground wires. Also have you checked the sensor resistance, it should be around 10 ohms with no pressure and go up to 100 and something with 10bar. If your's has a different resistance then you'll need a different resistor or will have to write a new calibration table. You will get a 560 ohm resistor from maplins or somewhere similar. I put my resistors at the ecu connector end to save the extra wire to the sensor!

Martin

Pants! I was going to earth the sensor back to the ecu through the fitting that screws into the dash 6 adapter. My fuel rail is plastic so it wont be earthed to the engine. That's how VDO's website had it. Although I guess they just earthed it back to the engine.

Sounds like it would be easier to get a new sensor.

[Jon K]

Sounds like it would be easier to get a new sensor.

It would be Martin is right. What do you budget for a pressure sensor? I have been using a Kalvico (AEM) transducer on oil and fuel pressure and love them.

[Ponk]

Sounds like it would be easier to get a new sensor.

It would be Martin is right. What do you budget for a pressure sensor? I have been using a Kalvico (AEM) transducer on oil and fuel pressure and love them.

Oh well. It was an ebay bargain so I can't complain too much.

Budget is as little as possible really. Can anyone link me to the right sender on ebay? Is £50-60 the going rate?

[mefmotorsport]

OK, you've got the wrong sensor really, the one that DTA recommends has 2 terminals, the resistor of the sensor goes between the terminals and is isolated from earth. the sort you have has a switch to earth on one terminal and the sender to earth on the other. It's not ideal as you'll be tying the DTA sensor ground directly to the engine so you could suffer with introducing interference signals up the ground wires. Also have you checked the sensor resistance, it should be around 10 ohms with no pressure and go up to 100 and something with 10bar. If your's has a different resistance then you'll need a different resistor or will have to write a new calibration table. You will get a 560 ohm resistor from maplins or somewhere similar. I put my resistors at the ecu connector end to save the extra wire to the sensor!

Martin

Pants! I was going to earth the sensor back to the ecu through the fitting that screws into the dash 6 adapter. My fuel rail is plastic so it wont be earthed to the engine. That's how VDO's website had it. Although I guess they just earthed it back to the engine.

Sounds like it would be easier to get a new sensor.

Well it's OK if its plastic and not earthed but the main problem will be the resistance of your sender I think.

I just had a quick look at the pressure sensor scaling in the DTA software for the VDO 10bar sensor, a quick calculation shows that at zero pressure the 0.088V relates to a 10 ohms resistance of the sensor, at the top end, 10 bar, 1.237v relates to 184 ohms so that is the range you should be looking for from your sensor.

Of course if you know the resistance range of the one you have (or test it with compressed air and a pressure gauge and ohm meter) you could easily build a new calibration chart using whatever suitable pull-up resistor you decide to use. I wouldn't go lower that 500 ohms though as the resistor will start to get hot with low pressure and also you will start drawing considerable current from the DTA 5V rail.

Hope this helps,

cheers,

martin