p0171 p0174 - Getting it narrowed down

I bought a used 07 4x4 w/ 183k miles on it recently and am dealing with it throwing p171 p0174 codes. Using my bluetooth scanner it seems like the STFT stays within 4% at 1500, 2500, 3500 rpms, but it starts getting really lean when holding steady at about 4500rpms.

Pervious owner claims he changed O2 sensors, and cats. I cleaned the MAF. He claims next step was to replace fuel pump and included the one he was going to install with the purchase. It makes sense that the fuel pump is having trouble keeping up at higher RPM. There are no signs of sluggishness or anything. I wouldn't even suspect a problem if there was no code. The truck runs like a beast.

When the check engine comes on it is solid. The VSC OFF light blinks and the traction control light comes on solid, 4LO light blinks. All 4 lights come on at the same time. (4WD Hi and Lo work normally when code is cleared)

What do you guys think about this? Code keeps returning between 15-40 miles after clearing.

 

Definitely do not shotgun parts at your truck.

Buy or rent a smoke machine and smoke the intake to be sure there are no leaks. Lean bank 1 and bank 2 would have me looking super hard for vaccum leaks.

What is the number for STFT at 3000 RPM? Are you seeing something like +4%? What about at idle?

I would also have a careful look at all of the sensors in the exhaust stream to be sure they are genuine Denso sensors. If the previous owner replaced them all with low cost budget crap, that could be the root cause of this issue. The same would go for the MAF.

If you blip the throttle, what does the MAF read in grams/second right when it returns to idle? I would expect at least 11 g/s, anything less than that and I'd be suspicious of the MAF (provided the smoke test shows no intake leaks!).

 

I'll get these numbers and report back. Thanks for the starting point.

 

When the check engine light comes on it will disable all systems associated with the warning lights. But when the check engine light is cleared all those lights will normally turn off.

It basically goes into a raw data mode for the lights that are on. In other words those systems will not provide any driving protection while they are on. And the 4WD will not engage.

 

Yeah I initially thought it was an issue with AIP or 4WD (and I think I gotta the seller down a bit in price because of it) but the 4WD works perfectly fine when the codes are cleared. Happy about that.

 

Once you get the code sorted out all lights will stay off!