(1991 ford f150 4.9l) Replaced my MAP sensor yesterday because the truck was having issues starting unless i gave it gas, replacing it fixed that issue but now the truck stalls when going in reverse or sometimes when coming to a stop in drive and has a check engine light. Dont have an obd1 sensor so i did the eec test using a paper clip and the code that came back was 126 which is for the MAP sensor being out of range. Confused because i just now replaced it and if i put the old one back in it will go back to having the other issue again. Any ideas?

 

In addition to the MAP sensor, you need to have a proper manifold vacuum attached to it. The wiring for the MAP sensor needs to be good as well. I would make sure the vacuum line from the manifold going to the MAP sensor is in good shape and you have a steady 18-22 inches of vacuum at idle off the intake manifold.

 

how do i check inches of vacuum?

 

With a vacuum gauge. You might be able to borrow one from your parts store with a deposit. Vacuum and fuel pressure gauges are a must have especially if you have an older vehicle.

 

picked up a vacuum gauge yesterday and tested my vacuum today , reading 20 on the gauge. replugged the MAP and unplugged my battery for a few to reset the ecu , still have the check engine light and pulled the code and its still telling me MAP out of range. you think this might just be a faulty sensor?

 

Anything is possible, especially if an aftermarket sensor was used. OEM , doubtful it is bad.