Code 31

[25th LX]

I'm restoring an 89 Mustand LX 5.0, and running into some real problems with the EGR system. I've already replaced the EGR valve, the EVP, and the EVR. I'm pulling almost 28 Hg of vaccuum, and the system checks for voltage is good on the EVP. The EGR valve is actuating and holding, and I'm still geting the code. I'm looking for ideas, and does anyone know the voltage parameters for the EVR?

 

[1990LXDropTop]

I had the same EXACT problem. I went through two NEW EGR valves and the code still came up. The code kept coming up until I bought a new throttle body and spacer. So my guess is that your EGR spacer is really dirty.

 

[jrichker]

CODE: 31 (KOEO) - EVP circuit below minimum voltage. Vref (5 volt reference voltage supplied by the computer) missing or broken wire or bad connection in circuit. Use a DVM to check for 5 volts on the orange/white wire. If it is missing, look for +5 volts at the orange/white wire on the TPS or MAP sensor located on the firewall near the center of the car. Use the black/white wire for the ground for the DVM. With the sensor removed from the EGR and still connected, press the plunger and watch the voltage change on the brown/lt green wire.

Pull the passenger side kick panel and measure the voltage at the computer. You will need to remove the plastic cover over the wires and probe them from the backside. A safety pin may prove very useful for this task. Use pin 27, EVR input (brown/lt green wire) and pin 46, signal ground (black/white wire) to measure the voltage. The orange/white wire is Vref and should always be 5 volts -/+ .25 volt. Be sure to measure Vref at the EGR sensor to rule out any broken wires or bad connections.

Clean & check the 10 pin connectors if you have voltage at pin 26 (Orange/white wire) on the computer and not at the the EGR, or TPS sensors, but it is present at the MAP sensor

 

[25th LX]

I shot all the voltages, and everything came up good. After three weeks of troubleshooting this thing, I finally fixed it. Just for grins and giggles I went ahead and pulled the EGR valve again. The diaphram was working properly, and everything checked out good, but it was the EGR valve. I talked to the Ford dealership's emissions guy and he told me why. Aftermarket EGR valves have a tendency not to have the right sized plateau inside on the diaphram backing plate. It doesn't keep the EVP sensor pushed far enough in at idle to generate the right voltage reading to the ECM. I replaced the EGR with one from the dealership, and the problem is gone.....THANK GOD.

 

[HISSIN50]

you are not the first person to have a miscalibration with the position sensor and valve. it can happen on oem stuff as the seat wears as well.