Hi all. I have been having this issue for months failing my State emissions testing. I throw a P0171 & P0174 code. No vacuum leaks, fuel pressure and flow are spot on, New spark plugs, New cap and Rotor, New Ignition Control Module, New Crank and Cam sensors. I am lost on this. Any help or input would be great. Top freeze fram data is with MIL on. Bottom is with it off still have 2 monitors not ready, Purge and Cat monitor. The light will turn off if engine is under load like in 4 wheel drive or hauling a lot of weight.

MIL STATUS On
ABSLT TPS(%) 17.6
ENGINE SPD(RPM)1676
CALC LOAD(%) 17.3
MAF(LB/M) 3.95
MAP("HG) 20.1
COOLANT(øF) 187
IAT(øF) 32
IGN ADV(DEG) 33.0
SECOND AIR ATMOS
ST FTRM1(%) 7.0
LT FTRM1(%) 25.0
ST FTRM2(%) 9.4
LT FTRM2(%) 25.0
VEH SPEED(MPH) 29
FUEL SYS1 CLSD
FUEL SYS2 CLSD
O2S11(V) 0.830
ST FTRM11(%) 10.2
O2S13(V) 0.750
O2S21(V) 0.700
ST FTRM21(%) 10.2
PTO STATUS Disen
OBD2 STAT CA
FRAME: 21 TM: 67.1

-------------------------------------------------------------

MOD $10 ----
TROUB CODE P0171
ABSLT TPS(%) 5.9
ENGINE SPD(RPM)1527
CALC LOAD(%) 9.8
MAF(LB/M) 2.24
MAP("HG) 12.7
COOLANT(øF) 187
ST FTRM1(%) 6.3
LT FTRM1(%) 18.0
ST FTRM2(%) 8.6
LT FTRM2(%) 15.6
VEH SPEED(MPH) 36
FUEL SYS1 CLSD
FUEL SYS2 CLSD

 

Exhaust leak? Air pump on that year of engine?
Can you post the STFT at idle and at 2,500rpm?

 

if exhaust leak and air pump check out you may need to check the fuel injectors (spider). Sometimes you will also see a po300 code with po171 & po174 may also feel just a little rough during 35 mph driving, if this is the problem.

 

How have you determined that there is no vacuum leak? A lean condition that reduces at higher load would sound to me like air getting in that isn't getting measured. Assuming the fuel pressure is good and injectors are clean, either a vac leak or intake hose failure (after the MAF sensor). That is where I think I'd begin to look.

 

You also must do the re learn for the crank sensor. This must be done with a high tech scanner. The cheap ones cannot perform this function so you will most likely fail emissions tests .

 

P0171 & P0174 can and will set if fuel pressure and or volume is low. You said fuel pressure was "spot on"... what is the pressure and leakdown at the service port, and at the fuel filter outlet? Pressure reading at the service port will give the LOWER of regulated or maximum pump output pressure. Testing at the service port only tells half of the story

Lazy or dead oxygen sensors will set those DTC's too.

As mentioned, replacing the crankshaft position sensor requires a crankshaft position sensor relearn, AND replacing the camshaft position sensor requires camshaft retard to be checked/adjusted. If these are not done, the engine will still start and run, but injector and ignition timing will be incorrect, guaranteed.