2001 ranger 4x4 with 4.0 SOHC I am getting codes P0171 and p0174 bank 1 and 2 lean changed my intake manifold o rings also cleaned my MAF as well as last year replaced the DPFE sensor due to previous issue could it be that my MAF is shot or the DPFE already bad again I already replaced the common pcv tube rubber elbows and did a smoke test no obvious signs of a vacuum leak that I could see am I missing something ???

 

Any help would still be great been 2 weeks still no luck on figuring this out

 

DPFE sensor is for the EGR system and doesn't use vacuum, except to open the EGR valve, so would be an unlikely source of Lean codes

After engine is fully warmed up, and idling, unplug the 2 wire connector on the IAC Valve, RPMs should drop to 500 or so, or engine may even stall, this is GOOD, it means no vacuum leaks
If RPMs do not drop then there is a leak

Lean codes mean the computer is having to open the fuel injectors longer than it calculated, to keep the upstream O2 sensors in the correct voltage range
So engine is never actually running Lean

A vacuum leak can cause lean codes because computer is not getting correct data from MAF sensor, so its calculations are off
A dirty MAF sensor cause lean codes because its under-reporting air flow
But lower fuel pressure can also cause lean codes, 2001 Ranger should have 55psi fuel pressure at the injectors, if its 25psi then computers calculations would be off because less fuel is flowing in when injectors are opened

Are there any other running issues, i.e. does it run well at higher speeds, highway speeds, no lack of power accelerating at full throttle?

 

• I did the test and unplugged the IAC a few days ago and the engine bogged down to 500 then came back up to 650 rpms the engine doesn’t seem to run rough and it does fine at highway speeds the freeze frame data shows each time I clear the code and recheck it when it comes back that it always triggers around 2,500 rpms I dong know if there is any significance to that I am curious if my car quest fuel pump that I replaced 2 years ago is already junk I know that car quest isn’t a great manufacturer also referring to fuel pressure where is the port located to check fuel pressure on a 4.0 Sohc thank you for your help I am very stumped as to what is the cause of this problem at the moment I don’t have any hard starts and my truck doesn’t seem like it’s starving for fuel or anything like that

 

Ron I appreciate your help could you also attach the procedure for checking fuel pressure example being key on engine off or running things of that nature

 

The early 2000's 4.0l SOHC may not have a test port for fuel pressure, it looks like a tires air valve, a schrader valve, so if you don't see it there is no easy way to test the pressure

You would need a "man in the middle" type fuel pressure test kit, it would have a connector that fits on the fuel line connection at the engine, so it is installed between fuel rail and fuel line

Since engine RPMs do drop when IAC Valve is unplugged then its not a vacuum leak
Its possible that the MAF sensor is reading low as RPMs go up so codes come above certain RPMs, but.............lower fuel pressure would cause same thing

 

I have an update on potential problem after doing a third smoke test notice smoke leaking from both sides of my throttle body shaft out of the TPS sensor as well as where the throttle cable hooks leaking underneath of the coil spring is this potentially my vacuum leak that I have had such a hard time looking for ??? Thank you for all your help much appreciated

 

Its possible the bushings are worn out

 

would that be the source of my vacuum leak

 

You are there I am not?

With engine running have you tried to spray, soapy water or Quick start(ether) at that location to see if RPMs change, if either is SUCKED in it will cause a change in RPM