Code P0171?

Thank you but now I have another question. After I secured the AF housing, I'm driving around with my scanner connected and every time I clear the code it comes right back so that wasn't the problem. When I replaced the vent valve all codes pertaining to the evap system stayed gone. Now this lean code came up which didn't before. My attention is now on the purge valve. Could the purge valve be causing this code and not specifically identifying the evap system? I'm going to test the purge valve. The filler neck to the tank is pristine as well as the tested gas cap. I did my own smoke test and found no leaks in the evap system. If purge valve tests okay, would I be travelling the right road to focus on the intake manifold bolts and or the MAF sensor? Thanks again for your time.

Okay, I'm now onto the fuel filter and MAF sensor but I can't get a straight answer on where the MAF sensor is. Any other vehicle is in plain view. One guy says it's here; another says it's there. Yet another says there's none at all. Obviously two of those answers are bogus, which is it? I have no problem identifying it on any other vehicle. Incidentally, it took several days for the evap code to return. I tested the purge valve, and it was clicking only a fraction of the time. That would tell me why the code didn't come back right away because it was working some of the time. So far, the evap code is gone, but the 171 came up immediately. I understand the fuel filter was recently replaced, for security of my waning sanity, I'm going to replace it again. Still need a MAF location or if it even exists.

I would like to add that this vehicle is not displaying signs of low fuel pressure. I'm totally aware that slightly low fuel pressure may cause problems. But there have been no misfire codes which is a relative symptom. This truck hauls ass. It's very fast and may even beat my crown Vic interceptor that has a V8. It starts and idles fine, doesn't run rough. I have smoke tested right into the intake and smoke tested the evap system and cannot find a vacuum leak. I'm also confused as to how the 171 code comes and goes. Does it run lean when it feels like it? As long as the comp is displaying evap codes, the lean code is absent.

No, sorry. Basic scan tool here. I really just need to know does this 2003 4.2-liter engine have a MAF sensor or not? If so, where is it please thanks? In summary, the vehicle started out with evap issue codes. Removed, tested and replaced the vent valve as there was no reaction when I applied current directly to it. Code remained absent for several days but then displayed the lean code but evap code did return. Removed and tested and replaced the purge valve as it was reacting intermittently to the current applied directly to it. Smoke tested the evap system and then went directly into intake and found no leaks. The gas cap was tested and ok'd when I failed the emissions test. I then replaced the fuel filter as I found no record of it being done and as of now I've got no codes but need to drive cycle some more. I'm left with the MAF sensor which I can't easily identify on this engine. That's about the end of my rope of expertise. If I can't clean or replace a MAF sensor and the mil stays lit, I don't know what else I can try. I have not been able to put a gauge on the line at the fuel filter but again, there is no misfire codes or anything else indicating low fuel pressure. Starts, idles and runs like a raped ape, no signs whatsoever of low fuel pressure. It is past due for passing smog test and now I'm having to absorb slack from this vehicle being down. Can you please tell me, MAF or no MAF? Or any other suggestions I can try at my level. With the current state of this country and the gouging of customers going on, bringing this vehicle in at 140 dollars an hour just isn't possible right now. I appreciate your attention.

The lean code keeps coming back, like really quick. Not even having to drive it. I found a receipt in the glove box where a service center had reviewed these codes and there was a general statement on the receipt being the most likely fix reprogramming the PCM. Is this something that happens by completing drive cycle scenarios? Does it happen over time? Or do they need to remove the PCM? Is this even an accurate explanation? I can't see why, but again I know nothing of the vehicle's history with the previous owner. I do know that one year ago the vehicle passed emissions and it also had major ac work done, like I think the compressor was replaced. This same mechanic is the one stating about the PCM on the receipt. Would changing the compressor warrant a reprogram of the PCM? I'm about at the end of my rope unless you have another idea. Also can I ask you about another vehicle here or should I start a new thread? The trailblazer is my landlady's, and the new question will be about my crown Vic interceptor.

Okay. I'm still chasing this thing, but I did manage to score a better scan tool, and this is what I saw. First off, which I thought was weird, was immediately upon starting the system went into closed loop way before it reached any temperature. Is that because of heated o2 working? This is the real issue I found. The small tube that connects the fuel pressure regulator to the airbox on top of the engine, when I wiggle the tube the fuel trim bounced back and forth from extreme negative to extreme positive. I think 19.53 is the maximum fluctuations either the scanner app will display, or the computer will allow in not sure but regardless, the slightest touch and it will go from neg19. 53 to pos 19.53 instantly. The driver complains of a gas smell occasionally. The tube is not clogged, and I couldn't find cracks in it. Should I replace the tube or the regulator or both. I hope I'm making sense. Thanks for all of your help so far. How you keep up with all of this I'll never know but good job.

Yes, sir that's the one. I could almost blow on that tube, the slightest touch sends the stft from all the way negative to all the way positive and another touch sends it all the way back to the negative again. Meaning -19.53 to +19.53 in an instant, not anything in between. That tube appears to be airtight so it's telling me there's something amuck with the regulator. One moment it's dumping fuel into it the very next it's trying to take it away. I would suspect that's why she only occasionally smells gas. Incidentally, I'm also getting the p0442 code simultaneously with the p0171 for the first time. Before it was one or the other. The purge system, valve and solenoid both tested faulty and have been replaced. There's no change in numbers while applying brakes nor 1500 or 2500 rpm revving. I have not seen a drop of fuel from that tube or anywhere. The exhaust stinks like dead birds but this vehicle has no problem starting, staying running and it hauls ass still. No hesitation and only a very slight rough idle. The cap has been tested; I've done smoke testing as well as carb cleaner testing revealing no leaks. Should I buy the regulator? I've got one shot at getting it. I can only afford one more thing I have to get it right. Thanks

I suppose I'm going to check again. You'd think I would hear it sucking if it's enough to cause that much of a fluctuation. I also wanted to add that I was trying to create some disturbances while watching the live data and the small plastic cone or whatever it's called that sticks out from the front of the air filter housing that the air enters the air filter box. I was holding a rag, my hand, and a piece of cardboard over the hole. You'd think the engine would bog down or maybe even stall from the air being choked off but there was no affect. I don't think any numbers even changed almost like it's getting air from somewhere else. I also read somewhere, not saying it's true, but I read that the maf less system with the map sensor fuel trims won't be affected by a vacuum leak. Can you confirm or deny any of that? Thanks again man. Ive got to be getting close. This thing has more than one issue that's compounding the other.