Hello, I recently have been getting OBD codes p0171 and p0174(lean both banks) along with a few other vacuum related problems. I suspected that the cause is a faulty lower intake gasket. However, I wanted to explore the symptoms further before tearing into the engine so, I bought a OBDII tool with live data so that I could see fuel trim data. Here is the problem, all of the fuel trim parameters read -100% and never change. I have tried the scan tool on other vehicles and have no problems reading any live data parameter so the tool is working properly. I thought all 1996+ vehicles supported live data. am I wrong? Or is my computer doing something odd?

 

Btw, all other applicable live data parameters are displayed with no problems. Also, the vehicle runs reliably with no major issues.

 

Yes, that 100 on fuel trim is not uncommon on the early Ford OBD II, they didn't use standard OBD II protocol until, I think, 1998, might have been '99.

Yes, some of the other data will often work OK.


Also check PCV valve and hose for vacuum leak

 

Thanks, I was afraid of that. maybe a newer pcm or reprogram the current one to support fuel trim data if that is a possibility.