Engine Dreaded 5v reference

[89foxstang]

My 89 fox has no 5v reference when plugged into mass sensor. Well people seem to thought the sensor was the culprit. Well I bought a new one and the same problem still. I can backprobe the harness unplugged and i got my 5v. Any ideas?

 

[Mustang5L5]

So you have 5V on the tan wire when you backprobe? What about when you front probe by unplugging the sensor with key on? Are you able to get 5V from the physical connector that contacts the MAF pins?

You can also test at pin 50 on the ECU which is your signal return. Pin 9 is your 5V reference.

 

[89foxstang]

So you have 5V on the tan wire when you backprobe? What about when you front probe by unplugging the sensor with key on? Are you able to get 5V from the physical connector that contacts the MAF pins?

You can also test at pin 50 on the ECU which is your signal return. Pin 9 is your 5V reference.

When i backprobe with mass unplugged i get 5v. Soon as plug in none