Unsolvable P0171 'System Too Lean' Code

You really should find a shop that has a smoke tester. Smoke testing is probably the best way to find multiple vaccuum leaks if they exist. If that is okay, I would rule out the MAF, spark plugs and wires as well as o2 sensor due to those being replaced. Next, I would check fuel pressure on this bad boy. Make sure it is within spec even while driving it. Make sure it is not allowing pressure to go away even after you shut it off, that would indicate a bad check valve. Or maybe even a faulty fuel pressyre regulator. Check your coolant to make sure you are topped off as well. That can cause a shitstorm of problems if you are too low.

If everything above checks out fine, get a cylinder leakage test performed on the engine. I'm not saying that you have one, but you MAY have a blown head gasket which is possibly allowing unmetered air into the engine. (Very rare, but I have seen it happen before.)

 

Lol, i dont know why ive started to do that, haha! But i have quite a few times recently hu? I guess ive built up respect and trust for you these last several months, especially with lovemytacolots ongoing saga with her nasty engine problems. So i suppose i feel like ive sorta gotten to know you, atleast as much as one can do from reading internet forum replys lol. Just take it as a sign of respect, your knowledge base is vast like an old timer! Thus the "ole koditten" title I've dubbed you, haha!

You havent taken it as a sign of disrespect have you??

 

No worries. Thanks for the compliments.

 

I'm still taken back to Lovemytacolots's thread. Her first problem with the original engine burning down was a "lean condition" as well. I remember her finding out it had bad injectors, but am having a hard time comparing the problems in this thread to bad injectors.

Maybe there is a clogged fuel filter and the thing is leaning out on wide open throttle.

If there is a vacuum leak, there should be a code thrown for that right away. That part of the system is very sensitive. The op is only getting a lean condition on WOT.

Also, I'm trying to figure out why the OP claims that the vacuum leak sounds louder under throttle. Most times, an engine loses vacuum as it is loaded. I wonder if there is a breach on the air filter assembly of tubes and only opens when a large amount of air is suck in? I love a good mystery.

Lean condition= too much air for the amount of fuel, not enough fuel for the amount of air. What conditions must occur for this code to be thrown?

Just thinking out loud here. Hoping it will help others come to some sort of conclusion. With the large number of people on here, we must have a huge amount of knowledge to work from.

 

If it is only a lean condition being thrown at WOT and OP has a blower,that would indicate to me that he has the well known lean condition due to poor factory tuning if I remember correctly. The first gens are supposed to be notorious for it and a 7th injector usually helps.

 

I wish I knew more about these super chargers.

Obviously, the SC is able to cram more air into the combustion chamber. The fuel pump, fuel pump regulator and injectors also need to be able supply more fuel to burn then a normally aspirated motor. If the injectors are restricted from supplying that fuel, you will get a lean condition? True?

I really hate throwing parts at a vehicle, but I would start simple and change that fuel filter. I'm just trying to go at this in a rational manner.

If it is not that, is there a chance the truck needs high flow injectors? I don't really believe that the 7th injector is the solver of the problem either. This engine/SC were designed to operate just fine without it.

 

The best way to combat fuel starvation on ANY forced induction vehicle is to ensure the proper flow rating fuel pump is in the tank and receiving a clean power and ground to it. A Walbro 255 LPH, AEM 320LPH, or Aeromotive 340LPH will be more than plenty for our engines, the size of it does not matter as the injectors will regulate the amount of fuel being injected into the combustion chamber, not the pump.

Next, the fuel injectors need to be the proper cc rating in order to be able to keep up with the demand which the engine requires to keep it happy at all AFR's. I'm not sure if he runs a 4 banger or a 6, but I know first gens are guilty of coming with undersized injectors with the blower kits. Aftermarket may be a different story.

If he has not touched the fuel filter in a long time, he should do it ANYWAY as a maintenance item, as that can severely choke out the engine at WOT.

If the injectors are either restricted or the bottleneck of the system because they are undersized, they will not be able to provide to proper air to fuel ratio required in order to keep the engine running happy at all RPM's. So yes, you will get a lean condition because there is more air than fuel being presented into the combustion chamber.

7th injectors have been proven to help the 1st gens. OE designs their stuff to keep compliant with ARB or in my case CARB emissions regulations, therefore that doesn't always mean they tune the computer to run the engine with the cleanest or best burn/ proper air fuel ratio at all RPM's in mind. Something for you to ponder about.

 

Wow I got a flood of responses in the last couple of hours, lol. Thanks guys, there's a lot of useful information being spoken here that is really helping me understand what my issue could be related to, and in turn it helps me communicate that with the service techs. I'd much rather go in having knowledge of the situation than be completely naive and at their mercy, especially when they claim that they "can't help me" because I'm under warranty and they aren't getting paid directly (but that's another gripe for another day).

I'm taking Monday off form work and driving down to San Diego from LA to get my truck worked on at the dealership I bought it from last month, I called them earlier and they promised they'd do whatever it took to get my truck up and running right. So there's that.

In all honesty, even though the local Toyota dealer told me they did "everything in the book" to try and resolve my issue, all I know for certain is that they replaced my MAF sensor, spark plugs and o2 sensor, and that's it. From the extensive reading I've done on this P0171 code (and from all the valuable info I've got from you guys), I know that there are a host of other reasons that my truck could be getting this code. Vacuum leak, fuel filter/pump, fuel injectors, a crack in my exhaust system, etc. For whatever reason, likely because I kept relying on my 3rd party warranty to cover expenses, this local dealership decided they were done with me. So come Monday, the original Toyota dealership I purchased my beloved '04 from will be taking care of it....hopefully once and for all.


By the way, I bought this '04 with only 24,500 miles on it (not a typo) last month. Dealer installed TRD supercharger, headers and exhaust when it was new. It's frustrating thinking I bought a practically brand new '04 (mileage wise) and now this is happening. But the fact of the matter is, it's probably just a small leak somewhere and that this whole ordeal has gotten unnecessarily out of hand.

To answer a few of your questions, the first couple of times the code got tripped it was under wide open throttle. The last few times though (after the dealership reset the code) it came on almost immediately after driving away under low throttle. My mileage has also gotten a lot worse in the past few days, I drive the same commute daily so it's easy to tell. Despite that though, the truck idles fine and doesn't hesitate or miss a beat when starting up.

My primary concern at the moment is that I've been driving lean for over a week now, and that's not good. From what I gather, it's putting a lot of strain on my pistons and over time it will start to take it's toll. So, rather than waiting until next Saturday to taker her in, I'm calling in to work on Monday and doing it then instead. I paid a pretty penny for this '04 (my dream truck in every aspect) and I'm not letting her go down over a stupid P0171 code goddamnit, lol

Thanks for all the replies and I'll be sure to keep you all posted on what happens Monday.

 

So even though she's sick, I got my super sweet TRD grill emblem in the mail today

I started her up to see if my lean code would miraculously disappear after putting the emblem on, but nope

 

Bummer. Usually those badges are good for fixing that problem and adding 10 hp.

 

I figured the blower could use a little help

 

On a side note, how in the heck do you pop the hood open now? Where is the latch now? On mine/stock the latch is in the grille.

 

The latch is just behind the grill, you can see it on the second pic

That's strange, I remember my '99 being just like the '04 I have now

 

My bad, not the actual latch, but the handle thingy that you pull to open the hood.

 

You mean the lever inside the cab that pops the hood? I'm a little lost lol

 

I wish I could explain. Hold on ill take a picture of what I'm talking about.

 

This lever right here. That opens the hood.
Mine is in the grille

 

I had to look up a video to make sure I'm not crazy lol. It's exactly where his hand is.

 

I've had 4 Tacoma's over the years. None of mine were like that. On all mine, the secondary latch is is reached after you release the inside latch and the hood pops up a bit. Was that a 2001 thing?

 

Hu, strange. I too have never seen the latch accessed through the grille like that...