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fourings

Fuel and oil pressure sensor

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Hi All,

I got a G4+ ttlink pnp on my Audi A4. 

I've wired a 150psi fuel pressure sensor to AN Volt 2 and assigned a calibration table and it is reading 155psi. Whilst unplugged I have 5v across the ground and 5v in and 0v across signal and ground. When I plug it in and back probe I'm getting 4.6v across signal and ground.  I tested the same with a spare sensor and I'm getting the same result. Any idea as to what I'm doing wrong or could be the issue? 

 

I've also got an AEM x series 150psi oil pressure gauge wired in to AN Volt 7 and this too is not reading correctly via the gauge and pclink, it just reads 11psi on gauge and 13.8psi on pclink. The instructions says white wire to analog input on ecu (AN volt 7?) and the BROWN wire must be connected to the negative of the analog input of the logging device orECU.  If the logging device or ECU does not have a differential analog input (both a dedicated positive and negative terminal for the analog input) then connect the BROWN wire to the shared signal ground.  If the device doesnot have a dedicated signal ground then as a last course ofaction, connect it to the power ground of the logging device.

 

I connected it to the power ground, could this be the issue?  Thanks in advance! 

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For your fuel pressure issue I suggest you attach your map so we can first check your settings are correct.  From your voltage readings though it almost sounds like you might have the pinout wrong.  I would have expected more like 0.5V between sig and gnd at rest.

For the AEM gauge, the brown wire should be connected to sensor ground.  If connected to power ground there will often be an offset - and that offset will often change with electrical load such as when headlights or fans switch on.  Having said that an error of 2.8psi from a 150psi sensor is only 2% so its not too bad.

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19 minutes ago, Adamw said:

For your fuel pressure issue I suggest you attach your map so we can first check your settings are correct.  From your voltage readings though it almost sounds like you might have the pinout wrong.  I would have expected more like 0.5V between sig and gnd at rest.

For the AEM gauge, the brown wire should be connected to sensor ground.  If connected to power ground there will often be an offset - and that offset will often change with electrical load such as when headlights or fans switch on.  Having said that an error of 2.8psi from a 150psi sensor is only 2% so its not too bad.

Cheers for the prompt response Adam.  

I've attached a screen shot of the cal table or do you want the pclr file? I double checked voltage across signal and ground it is 0V. I depinned pin 29 for the fuel pressure sensor as I do not need the air mass meter signal. 

I think I've just sorted the oil pressure issue, I found a wire that had come out from the harness in the back of the gauge.. It is reading 1.5 psi at rest. Would sensor ground be pin 27 and what would be the best way to splice right at the ecu? 

20171106_175110.jpg

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15 minutes ago, fourings said:

I've attached a screen shot of the cal table or do you want the pclr file

If you attach the map I can load it into an ECU and put a simulated signal into it, that is often a quick way to eliminate settings as the issue.  From your screenshot it looks ok but there are other influences such as the analog fault settings that could be at play. 

 

18 minutes ago, fourings said:

Would sensor ground be pin 27 and what would be the best way to splice right at the ecu

Yes pin 27 will be good.  splice location is not critical, you can do near the ecu or near the air flow meter plug.

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Ok, your map all works ok on the bench.  You likely have a wiring or sensor issue.

Below is the most common pressure sensor pinout although I'm sure I have seen a variation.  Does your pinout match this?  Gnd and 5v swapped maybe?

ycSNyes.png

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4 minutes ago, Adamw said:

Ok, your map all works ok on the bench.  You likely have a wiring or sensor issue.

Below is the most common pressure sensor pinout although I'm sure I have seen a variation.  Does your pinout match this?  Gnd and 5v swapped maybe?

Thanks for checking that out for us Adam, much appreciated.

I'll have to check tomorrow, that could very well be the issue as the spare sensor behaves the same.

Chances are I haven't mirrored the diagram. :rolleyes:

 

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