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MAP Sensor Not Reading - Low Voltage - VR4 Link

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Hello,

I am having a persistent issue with my MAP sensor reading on my 1990 Eagle Talon.

I have tested 2 confirmed working AEM 5 bar sensors. We have checked the wiring a have confirmed 5 volts and have a good ground with a multimeter and test light.

I am getting a consistent fault code 14 for an error low value. When the error low value is set to 0.00 from the default 0.05V the car will refuse to start and run. With the error low value set to 0.05v the sensor will show 1.00v in the runtime values menu and MAP (psi) of 14.5 and a MGP of 0.00. With the car running these values do not change. When the runtime error value is set to 0.00v the sensor shows no voltage in the runtime values menu and the MGP and MAP values invert and will read 14.5 for MGP and 0.00 for the MAP.

I am stumped as to what the issue can be as both MAP sensors I have tried are working and the wiring is correct.

I have attached a copy of my tune file as well as screenshots of my runtime values with both error value settings.

Hopefully the tuning wizards here can help.

 

IMG_20190909_200921.jpg

IMG_20190909_200944.jpg

Eagle Talon 9.9.19.pclr

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You have a wiring problem. It sounds like you checked a lot of it already, so maybe a pinout problem on the sensor? Have you checked continuity of the "signal" wire back to the right pin on the link ecu? (an volt 2 should be pin10). It could also be that somehow that signal wire is grounded somewhere else in the chassis - unplug the sensor and the ecu and with a multimeter check for continuity from that pin to ground, and from the pin to each of the ground wires in the ECU plug. One way or another, the ECU is seeing ground on that MAP input, not a real signal. Tuning cant fix that.

Your actual received voltage on that input is 0v. When the ECU considers this a "real" value (not an error condition), it reads this as 0kpa MAP (so -100kpa/-14.5psi MGP), which will throw you into a bad part of your tune and it wont start.

When you tell it 0.05v is the threshold for error condition, this causes it to go into error state and use the default value of 100kpa (anv2 error value), which just happens to equal 1v on that calibration by the looks of it. This is going to be very close to what your MAP really is during startup, so the engine starts. It probably runs like a dog though because it wont be seeing 100kpa at idle so again you will be in the wrong part of your tune for fuel/spark.

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A quick check to confirm your wiring would be to measure the voltage on pin 10 at the ECU header with a multimeter.  It should read about 1.3V at atmospheric pressure. 

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Went through and checked the wiring. For some reason the company that originally wired the car pulled the power and ground from the OEM maf wires but was using the an5 narrowband signal wire for the map sensor.

Switched the map sensor to an5 and it's all working now.

 

Thanks for everyone's help.

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