P0171 code under hard acceleration

Hey fellas

2005 tundra v8 127000 miles. I am getting p0171 code system too lean bank 1 code when i accelerate hard. Around town truck drives great. But if I really punch it code pops up. The code seems to go away on its own after a while. I’ve recently replaced my upper and lower o2 sensors, maf sensor and spark plugs. I thought it might be a vacuum leak but I can’t find one anywhere and all the hoses seem to be in good shape. Thought maybe Failing fuel pump? Manifold leak? I’ve run a few bottles of injector cleaner. Anything else that i should try? Thanks for any advice

 

I was thinking vacuum leak or fuel pump or manifold gasket

 

The large air hose between the MAF and intake plenum is highly suspect with its many ribs and folds. Under load/stress it will flex exposing tiny cracks between the ribs. Use OEM for a good fit and long life. Luck.

 

Couple things I'll say.

First, it's really difficult to see cracks in a line. The ends of the lines love to split and let hoses slip off. I'll leave you with the video below that shows a classic oldskool way of finding an intake/vacuum leak, which is what I'd be doing first, on the driver's side.

Second of all, the air/fuel ratio sensors (upstream O2) are responsible for telling the ECU the mixture of combustion coming past the exhaust manifold, and that info is what the ECU uses to decide whether it's burning rich or lean, and adjust. They're super important. If this problem was there BEFORE you replaced the sensors, and replacing the sensors didn't fix it, great. If it started AFTER you replaced the upstream O2, that's a problem. Maybe you didn't use Denso brand sensors, or used universal sensors which require cutting harnesses. Both are huge mistakes.

I doubt it's an exhaust leak, maybe I'm thinking thru this wrong, but I'd expect an exhaust leak to cause the O2 sensors to read in a way that would encourage the ECU to spray more fuel, resulting in rich condition. But maybe I'm nuts.

Lean codes ... either too much air or too little fuel into the cylinder, most often. Given the ECU is measuring how much air volume is coming in using the MAF, so it knows how much fuel should spray, and you've changed the MAF, it may be safe to assume it's not a matter of "known" air volume.

Given there's no fuel filter on '05-'06 thus that won't be the issue, that a fuel filter is clogged, and causing failed delivery. But again, give it's only 1 bank that's lean, logic would suggest it's not the issue, it would impact both banks.

To that point, knowing it's only on bank 1 (P0171), i.e. driver's side only, and the fuel flow is [Pump -> bank1 -> bank2 -> return to tank], if bank1 wasn't getting enough fuel, then I'm highly skeptical it's the fuel pump also. If it was the fuel pump, I'd expect to be lean on both banks. If you'd thrown a code P0174 (too lean bank 2), I'd be more willing to believe it was a pump issue, but I'd also tell you to replace the vacuum line that runs from above the middle 2 passenger side cylinders and over to the intake (which is still worth checking/replacing for P0171 code, get on it!!).

The vacuum hose you'll really want to verify is this one, cut ¼" off each end and replug or just replace. Just for shits and giggles, try replacing it, I believe it's a 4mm ID vacuum hose, you can get in bulk at the auto parts store.

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Here's the intake leak finding video. Carb cleaner works, as do a few other things in a pinch. Depending what you use, you'll be looking for either a surge in RPM, or a drop in RPM. Give this a shot on the driver's side.

https://www.youtube.com/watch?v=awbQmz06emY​

 

So I replaced the hose as you suggested. And tried using the carb cleaner trick to find the leak but to no avail. However I was looking under the truck discovered that the quick disconnect at the fuel tank is weeping. Wondering if that’s contributing. Is this any easy fix? I am not sure whether it’s the supply line or return. I am guessing that it is under pressure.

 

Wow, that's a killer find. And yes, 100%, absolutely I think you just found your problem! Any leak in the fuel lines would cause this, because it would detract from pressure in the system when hammering it hard. Any time you jam on the pedal, that fitting would've been leaking more, and you're lucky it wasn't in the engine bay and didn't start a fire. I'd have NEVER thought to look or even suggest looking for that!

Note the top fuel line fitting doesn't appear pushed in all the way compared to the other, see my marked up version here, note the hip to the left of the line on both, although. I'm fairly certain both are quick-connect fittings, and should latch in place when pushed on. If you push it in does it not latch? Push it all the way in, and twist a bit, see if it clicks in, then tug-test it.

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