P0171 Lean Bank Issue, Help !

thanks a bunch. going back at it on Saturday. will see.

 

ghs57... thanks for the upload. I read it twice and learned a few things. First is that running the truck out of fuel can trigger a P0171, didn't know that. The second is that a P0171 is a 2 trip fault didn't know that either. I don't have the Toyota special tool but I bet a propane enrichment to test the reaction of the sensors would work just the same.

 

I am thinking this is why I have the 0171 code.

 

Think I'm going to replace both O2 sensors and buy Denso only. But dang, Autozone wants $179 for upstream and $89 for downstream

Would someone be saw kind to look on Amazon for me to make sure I'm buying the correct denso sensors and post the 2 links here ?

 

From RockAuto.com:

$50.79 Downstream

$61 DENSO 2344189 Denso 234-4189 Oxygen Sensor

DENSO 2344189 Oxygen (O2) Sensor Alternate/OEM Part Number(s): 8946509250, 8946509260, 8946509270, 8946509280, 8946509330, 8946509340, 8946509350, 8946509360, 8946509370

$109.79 Upstream

$146 DENSO 2349001 Denso 234-9001 Upstream Air Fuel Ratio Oxygen Sensor with 10.6” 4-Wire Harness, for Auto Trans Equipped Vehicles

DENSO 2349001 Oxygen (O2) Sensor (Actually the Air/Fuel Sensor) Alternate/OEM Part Number(s): 8946734021, 8946735030, 8946735050, 8946735060

There is also a RockAuto discount in the vendor section.

I've changed both of these on every Tacoma I've owned. I'd also be curious about that vacuum leak you may have found. That may be the cause, or a contributor to, the P0171.

 

I had the P0170 once, after I replaced the air filter with an aftermarket. I cleaned the MAF and PCV, and the code cleared.

 

going after the intake manifold gaskets and plenum on Tuesday. Also will then check EGR valve. there was a leak in the manifold gaskets when I first bought the truck.

 

Yikes. There's ways to test for this stuff before buying new parts... check out South Main Auto on YouTube - he doesn't do many Tacomas but you can see what a quality diagnosis looks like where the problem is verified prior to ordering parts.



As far as vacuum leaks, you can check it this way too:



Same thing as a fancy smoke tester. You could put a plastic bag before (after in flow to the engine) the MAF to keep it clean.

 

Grab a sprayer bottle of water (carb cleaner works too) and start spraying around the upper portion of the engine while is running. Places where there are gaskets and vacuum lines to check for leaks. You will hear a slurping noise if there are any leaks. Obviously avoid the alternator. Try the free method before tearing into gaskets.

 

I had this code on my 4 cylinder, I relplaced the MAF sensor gasket that connects to the intake and it’s hasnt come back in a while , U should check it mine was brittle

 

@ OP.
What the guys said above--perhaps some troubleshooting is in order. I just replaced my intake gaskets a few months ago, in conjunction with re-sealing my leaking water bypass pipe. Not the hardest thing in the world, but not something to just "throw parts at", either...

 

I was talking bout the intake box where your air filter goes, thats where your MAF sensor adapts, there’s a rubber gasket that becomes brittle , only replacement is dealer

 

Stan, roll this back a bit. I don't see anything in here if this has an aftermarket intake or not, does it? So far I've only seen a few suggestions I would consider likely; but vacuum leak, aka unmetered air getting into the intake is the most common cause of this. How do i know? Because I added an aftermarket intake years ago that worked fine up until this winter. I removed it to make room for an auxiliary battery up front and replaced it with one of those garbage modular Specter kits from the auto parts store. Since then I've spent a small fortune on new parts, trying to fabricate one that eliminated the P0171 codes and check engine lights.

I've spent hours and hours researching the causes of these problems and seen all kinds of silly suggestions and butthurt in these forums: replace your turn signals, change the radio station, run premium unleaded, replace one injector, replace all injectors. P0171 means one thing only: too much air and not enough fuel. This is what is going on:

Start engine, air enters intake, past the MAF, into the combustion chamber. Right now the ECU is in "open loop" mode, meaning your o2 sensors down below are not yet heated up enough to begin the process required of detecting the oxygen content in your exhaust. Until they warm up, your ECU will not be able to detect whether or not your vehicle is running rich or lean and will not make any fuel adjustments, or trims.
Shortly after you start the motor the o2 sensors warm up and the ECU goes into closed loop mode. At this point, the ECU begins to detect whether or not your rig is operating properly: 14.5 parts air to 1 part fuel. More air= lean. When your ECU detects this, it adjusts the injector spray pattern, increasing the volume of fuel to the cylinders. These adjustments are short term trims, they happen constantly and vary. Over time, the ECU stores the patterns, which are known as "long term fuel trims".

The ECU will continue to adjust until it loses control, when your long term fuel trims reach 25% and the CEL comes on. Which means it has to compensate for the unmetered air entering the combustion chamber by adding 25% more fuel to the AF values. That's why your fuel economy sucks, and why you fail emissions.

What to do? If its an aftermarket intake, buy a can of carburetors spray and spray that bitch all around the intake, generally from the MAF back to the throttle body. If the RPM changes (increases), that's where your intake leak is. If no change, then check your MAF, again. Does your MAF have a good gasket seal to prevent air from getting in around it? When you cleaned it, did you spray MAF cleaner liberally all over the sensor, and let it dry before reinserting into the intake?

Right now I'm dealing with the same goddamn issue but I know its not the fuel injectors. It could be and others here on these forums have replaced theirs and it fixed the issue. I've had leaky injectors before and I smelled gasoline constantly in my cabin. Whatever you do, keep it simple and escalate as you go. Try removing the intake and reinstalling the entire thing. Check your seams, hose clamps, vacuum lines, but keep it simple.
One last thing to consider; if its an aftermarket intake I have heard that they can change the volume of air significantly enough that the MAF does not compute the data to the ECU properly and the ECU detects a lean code. Simply put, your ECU and MAF are calibrated to detect a specific volume of air within the intake. If your tube is too wide in diameter, the MAF will not detect air moving past at a sufficient velocity. Because of this the MAF calibration is inaccurate. There is nothing you can do other than replace the intake with a stock intake, or recalibrate the MAF with expensive equipment, sort of how a Dynojet Power Commander sits in front of the ECU of a motorcycle and tricks it by feeding intentionally supplied false data to increase performance.

Alright dude, I'm done. I'm working on my rig this weekend, if I fix the lean code I will let you know my solution. My approach:

1. disassemble the new intake I just installed and reinstall, reorienting the MAF in a different position (right now the tube is rolled so that the MAF is underneath it)
2. Remove these new plugs I installed last week and install new factory Denso plugs
3. Check all vacuum lines
4. try a different filter
5. swap the MAF out for an extra one I have
6. research more

 

There are two o2 sensors; one before the cat to detect the amount of oxygen in the exhaust and one after the cat to determine how the cat is operating. The first o2 sensor is used by the ECU to compare the data the MAF sent it (Here is how much oxygen moved past me), with how much oxygen the 1st o2 sensor detected.

 

Having read the Factory Service Manual's (FSM) description of the the Bank 1, Sensor 1 function, I don't believe that that is exactly the case. On pre-2000 model year Tacomas, there were two O2 sensors; both exactly the same. The function of those sensors sounds more like the what you describe above. The function of the Air/Fuel Sensor, which is still referred to as an O2 sensor most people, is described as follows under the diagnostic for TDC P0171:

CIRCUIT DESCRIPTION: The fuel trim is related to the feedback compensation value, not to the basic injection time. The fuel trim includes the short–term fuel trim and the long–term fuel trim. The short–term fuel trim is the short–term fuel compensation used to maintain the air–fuel ratio at its ideal theoretical value. The signal from the A/F sensor is approximately proportional to the existing air–fuel ratio. Comparing it with the ideal theoretical value, the ECM reduces fuel volume immediately if the air–fuel ratio is RICH and increases fuel volume if it is LEAN. The long–term fuel trim compensates for the deviation from the central value of the short–term fuel trim which is stored up by each engine tolerance, and the deviation from the central value due to the passage of time and changes of environment. If both the short–term fuel trim and the long–term fuel trim exceed a certain value, it is detected as a malfunction and the MIL lights up.

The diagnostic goes on at length discussing the function and how to troubleshoot the P0171 DTC. I included a copy in post #18 above.

 

The upstream o2 sensor is a wideband sensor, older vehicles did not use wideband sensors. It reports the lambda value, which the AF data is derived from. The downstream o2 sensor reports the cat performance, this is why the two sensors differ in price.

 

Ok here is what I've got-
Distance traveled: 92 miles
Avg mpg (mostly highway): 20.3
Fuel consumed (full tank): 4.5 gal
Avg speed: 55mph
Max speed: 73mph
WOT load: maybe 84% but did not reach this level easily or remain there. 60-75% was easier to maintain
2500 RPM (no load) MAF: 7-14 grams per sec
o2 voltages: avg readings, under 1v, more than .01v
Idle LTFT values: up to 30%
WOT LTFT values: every time reached 4.7% and no lower.
MIL lamp came on only if I idled long enough, P1071 code. At cruise, the mil lamp never came.

I think I have a bad MAF. I'm working with this cat from justanswer.com, hes a certified Toyota mechanic and analyzing my data. The only other thing I can think of is both of my valve cover gaskets leaking are affecting something, but I don't know.
MAF is clean, installed new OEM Denso plugs last night, and I added some Techron fuel system cleaner on a full tank before trip today. I do have a spare MAF but I don't have the small foam base gasket ring for it. Both of the MAF sensors I have are aftermarket from Amazon also.
The stealership wants like $170 for an OEM one. Fuck that shit

 

One more update. Disassembled the intake again, reassembled with some new 90° silicone elbows and a different cone filter that has a velocity stack integrated. Right away, both short and long term trims went negative and AF ratio ran rich, about 12:1. Took it for a drive and the ECU began to dial it back and maintain 14.7:1. Short and long term trims now are with 10% of each other. Will be interesting to see how this goes.

 

Any issues since Sad? I recently got the p0171 code. I have just the opposite. At idle, my long trim is -18 and short appears normal around -2.3 to +1.6. I have cleaned MAF. Just checked the fuel pressure and had a steady 43 psi. Replaced the a/f sensor which I had a bosch on there. It runs better but still falls flat when you quick hit the gas pedal. I figured with the negative trims I have, it isn't a vacuum leak. With fuel pressure test , I think I can rule out , fuel pump, filter. When I increase the rpm to about 2000, the long trim goes to -3.9 and every now and again it hits 0. The short numbers remain the same as at idle. I am thinking a dirty/clogged fuel injector???

 

Funny you ask; about two months ago, I decided enough of this shit and spent 30 minutes tearing out all of that aftermarket intake plumbing and auxiliary battery, electrical wiring for my fogs, inverter, and other accessories and replaced it all with factory intake components. I went to the stealership and bought a new airbox and intake tube; bought some air paper filters from Amazon and spent another 30 minutes installing it all. Immediately the codes disappeared; horsepower increased, and fuel trims stabilized. Plus it looks better I think.

I'll never do that again; and would advocate to anyone considering doing an aftermarket intake to think otherwise; the experience was a nightmare and its simply not worth it. Here, have a look- http://www.sadtaco.com/2018/05/tacoma-intake-problems-solved.html