Houston, we have (another) problem...

Hey everyone, it's me again. I've still been tearing my hair out trying to find the issue with my 2013 2.7L Base Model Access Cab that's been causing my PCM to fail intermittently. Now it looks like I've got another problem on my hands.

Within the last two weeks I've been getting a MIL/TRAC OFF lamp that keeps popping up when I'm going around 20mph. The first time it happened I didn't notice anything that would have caused a CEL to pop up, but as soon as I got to a parking lot I pulled the code P0171 - System Too Lean Bank 1. I cleared it, and went about my day, but noticed that it took a bit more cranking than usual to start it back up. Since then, the problem has gotten worse; I'm experiencing longer cranking times, and a significant decrease in power when accelerating from a complete stop. The CEL always seems to come on at about 20mph with the RPMs somewhere in the low end. I have no issues once I get up to speed, and have no problems getting up the hill on my way to work. It seems the issue only occurs at low speeds and low RPM when there's a lot of load on the powertrain.

So far I have cleaned the MAF sensor with dedicated MAF sensor cleaner, and cleaned the throttle body with dedicated Throttle Body Cleaner. Once I put it back together the engine would idle at 1000-1500 RPM, but disconnecting the battery for awhile and letting the computer re-learn the idle seems to have fixed that. However, I'm still experiencing longer cranking times, and the engine still struggles under load, producing a code P0171.

I've sprayed ether around the vacuum lines and intake gaskets to check for leaks, and haven't found any so far. The airbox filter is still relatively new and very clean. The fuel pump is only a year old; an AEM pump included in the URD upgrade with the external fuel filter mod, so I'm not confident there's a fuel pressure issue, but I also don't have the equipment to test it because from what I understand the standard fuel pressure gauges for Chrysler and GM vehicles don't work with Toyotas.

I've attached pictures of the freeze frame data from the last check engine light. I don't have a tool to read live data, but I'll probably swing by Harbor Freight and pick up a live scanner once my paycheck hits on Friday.

The only thing I can make of the freeze frame data is that the fuel trims are definitely too high, but I don't know how to interpret the other data so I'm not sure what else to look for.

 

I'd want to check fuel pressure as a first step, just because the pump is new does not mean it's good especially in today's parts market.

 

Personally, I would replace the maf sensor if you have already ruled out vacuum leaks and cleaned the maf sensor.

 

Do you or anyone else happen to know what a normal reading on the MAF sensor would be at idle?

 

G/s should be about equal to engine displacement in liters at hot idle.
You can also do a VE test where you do a WOT pull through 1st gear and record peak RPM, IAT, and peak MAF and enter the results in the calculator.
https://atgtraining.com/atg-volumetric-efficiency-calculator/

 

Another quick MAF test is to watch Calculated Load % while flooring it up a hill. It should go over 80%. If it doesn't MAF is suspect

But you really should try to check fuel pressure before throwing a MAF at it

 

I'll see what I can do.

 

Pretty sure you can rent a fuel pressure gauge from NAPA if you don't have one and don't want to buy one.

I hate fueling issues. I had a bad injector on my last vehicle, and the OEM didn't even make replacement injectors anymore. I had to buy a set of used injectors off CL to fix it. >_>

 

Here is the MAF Data I have.
I’m not a technician, so I’d let the other guys chime in on “how accurate this test is”.
But this is how Toyota say to check the 2TR


1.Connect the intelligent tester to the DLC3.

2.Turn the ignition switch to ON and turn the tester ON.

3.Select the following menu items: DIAGNOSIS / ENHANCED OBD II / DATA LIST / PRIMARY / MAF and COOLANT TEMP.

4.Allow the engine to idle until the COOLANT TEMP reaches 75°C (167°F) or more.

5. Read the MAF with the engine in an idling condition and at an engine speed of 2,500 rpm.

1. Standard:
   MAF while engine idling: Between 2.0 g/sec and 4.5 g/sec (shift position: N, A/C: OFF).
   MAF at engine speed of 2,500 rpm: Between 8.0 g/sec and 14.7 g/sec (shift position: N, A/C: OFF).

 

So I managed to score a fuel pressure tester, and either I hooked it up wrong or things aren't up to pressure.


We're looking at about 17psi at idle, with no residual pressure at shutdown. Could the lack of residual pressure be caused by a bad regulator or maybe a bad injector, or should I look into the fuel pump? The pressure stays relatively steady while the engine is running, but obviously it's less than half what it should be and it drops to zero once the engine shuts off.

**EDIT**
I also did notice that the return line seems pretty much dry, not sure if that's normal or if it adds to the diagnostic process.

 

That's your problem, if the regulator was bad you would see fuel in the return line as it regulates pressure by returning excess fuel to the tank.
I'm not sure how the modified fuel pump system works but me seeing that low of pressure on a non modified system would say bad fuel pump.

 

The modified system includes a new fuel pump and replaceable inline filter that's installed outside the gas tank, eliminating the in-tank filter that requires dropping the tank or pulling the bed off to replace. The filter that comes with the kit looks like this:
I decided to run another pressure test directly after the filter, which saw pressure just above 20psi. Then I pulled the filter off and drained it, which initially produced a clean fuel sample. Then I connected a brake bleeder to it and created vacuum inside, which produced a nice coffee colored sample, complete with sediment. Now I have something to work off of, and inevitably that'll involve pulling the bed off again to figure out if the fuel pump is clogged and how much sediment is in my fuel tank. For the time being, I removed the aftermarket filter and put the fuel lines back together underneath, and installed one of these under the hood so I can check the fuel quality with ease...

 

Careful running that design filter, most of those plastic filters aren't really designed for pressure.

 

It's definitely a temporary modification for diagnostic purposes, and I put the OEM hose in the glovebox so if the filter fails i can quickly be back on the road.

 

Well, as @Dm93 mentioned, it looks like the fuel pump was the issue. I just replaced the pump and now I've got great pressure and fuel trims are acceptable. Thank you everyone for the input

 

Awesome.
Good to hear.

 

Awesome result. This is a proper example of P0171 fixed by low fuel pressure and a fuel pump fixed it.
I need a fuel pressure tester to test mine.
I replaced the fuel filter, air filter and cleaned the MAF. None of those fixed my P0171 yet.

 

At least you can change the filter. Us 2nd Gen guys have to drop the tank. And the filter is more of a sock, than a “filter”.

 

The key is to do proper testing instead of blindly following the list of parts to replace for a code, lean codes can be tricky to diagnose due to the number of factors involved but if you know what to look for in scan data they are typically pretty easy to nail down the root cause.

 

"if you know what to look for in scan data they are typically pretty easy to nail down". Good info!

I have been 'real-time' monitoring the short and long term fuel trim percentages. Sub-10% on either (plus or minus) is good. Over 10% on either (plus or minus) is bad and may be what trips the P0171 CEL.

Does anyone know what specific sensor triggers the computer to trip the P0171 CEL?
One source says it is triggered by the up or down stream O2 sensor(s).

I also have a fuel pressure tester in the mail from Amazon. 44psi is the target for my 3.4l V6 4x4 with 5spd manual tranny.

This is my OBD2 scanner real-time at 60mph with slight acceleration at ~3,000 feet high. I'm betting those numbers are too high but it's just a 1-time snap shot.
They say over 10 (plus or minus) is bad. "CL" means closed-loop so that's good.
Short-term fuel trim % -4.7
Long-term fuel trim % 29.7