I keep having codes 171 & 174 come up on my 02 5.4. I have changed the fuel filter, the upstream ox sensors, the MAF-due to the part being defective and was replaced under warrenty. Plugs/coilpacks were done in July of 2009 along w/ a coolant flush and fill,tranny and transfercase and F&R differential flush and fill.PCV valve and corresponding hose to the TB has been replaced along w a dry rotted hose at the back of the TB.CHECKED AND CHECKED AGAIN FOR VACCUM LEAKS There is NONE!! Why are these codes so damn GENERIC!? I have changed just about damn near everything associated w/ these codes and the codes still come up My truck runs and ides FINE but uses a TON of gas! I filled up b4 work today and when I came home I used amost a 1/4 of a tank My commute is 28 miles one way to work.

PLEASE HELP!!!!!!!!!!!!!!!!!!!!!!!!

 

They are "generic" because they mean the same thing for ALL OBDII-equipped vehicles regardless of manufacture. This is in contrast to "manufacturer-specific" codes, those above P1000, which may be different for different automotive manufacturers.

Their being "generic" has no bearing on your inability to solve the diagnosis mystery.

 

My P0171 and P0174 codes were because my catalytic converters were shot- 230,000 miles does a lot. Dealer said one was clogged and caused so much back pressure it was fouling the O2 readings. I had new Maggie high-flows welded in and BAM. 19 mpg

Go under your truck when its running and listen for any exhaust noise. Might even be a leak.

 

I think that the OP means why do these codes have so many possible causes. I believe that he would want 1 code to require only 1 part to fix it. How did you check for vacuum leaks? Smoke test? Propane?

 

Have you replaced the DPFE sensor?

 

I observe the STFT readings while shooting brake parts cleaner at suspect points.

A smoke test is also valid, which, if I screw up where I spray the cleaner, I'll also have...along with the flame test. Shops that have smoke machines for evaporative emission testing should have the capability of checking an intake tract for any leaks.

The computer is usually too fast at correcting injector pulse width to observe by eye or ear any change in mixture when propane (or another flammable) gets sucked into the intake, but the STFT readings give the story.

DPFE sensors will normally cause their own DTCs if they're bad. There are exceptions. Similarly, a stuck open EGR valve can cause "lean" codes, but a good DPFE sensor will catch that condition.

"Lean" codes mean that the computer has reached its limit for compensating for a "lean" indication from the upstream O2 sensors. This will cause the engine to run rich and will cause excessive fuel consumption. Usually, these codes are due to an underlying mechanical fault that either causes excessive air, insufficient fuel, or a misreporting of the mass of the incoming air. In order of probability, the cause is usually due to vacuum leaks, a dirty MAF sensor, or insufficient fuel pressure.

 

Yes correct I just hate the fact that it is just a "generic" codes. I have done the brake cleaner,smoke test and the propane check for vaccum leaks and there is none. I broke down and bought a Motorcraft MAF today I have already repaced TWO of them from Car Quest i,e JUNK!! The light is still on but I know that the PCM has to "search" after a couple of drive cycles to make sure that the sensors are performing their jobs correctly.

 

What and where excatly is that part I am used to the older pushrod Ford engines please excuse the noob question.

 

You need to reset the PCM after making a repair like this.

Either disconnect the negative battery cable or pull the PCM KAM fuse for 10 minutes.

BTW, there are step-by-step instructions in the PCED to diagnose these faults instead of just buying parts...

 

Driver side of throttle body @ EGR valve:



Those two hoses would be routed under the EGR tube and connect to their respective ports on the DPFE

 

89, not to hijack this thread, but I need to ask you about the PCM KAM fuse. My owner's manual references 4 separate fuses having to do with the PCM. Which specific one is for the KAM? Last time I had to clear mine, I wound up pulling all 4 of them and next time I'd prefer to go to the right one first.

 

Red thank you! I thought thats where it was but I wasn't sure-the pic really helped What excatly does that "thingy" do?

 

dpfe = differential pressure feedback egr sensor. in short, it monitors pressure differences and tells the pcm how much exhaust is in the egr system

while you're doing all that checking - have you applied vacuum to the egr while the truck is running to see if you get a drop in rpms? that would at least rule out a faulty egr

 

Yes I have applied vaccum to the EGR and NO drops in rpm.

 

Ask and ye shall (we try to) receive. I had disconnected the hoses so another could get a view of them. Glad it helped