P0174 Learn How to Read Fuel Trims

I found the following online for the 4.0 V6

"The mass air flow sensor grams per second should be 3.3-4.7 at idle and 12.9-18.3 at 2500 RPMs no load"

In which case it seems my MAF sensor is fine. I plan to check the fuel pump and then procced with the AFR upstream sensors.

 

Just be cautious, if you start popping 'cat inefficiency' codes after, replace the downstreams too. I always recommend replacing in pairs (up/down stream) on the bank; i.e. if you replace one on a bank, replace both.

 

Glad you found the correct specs, apologies for any confusion my incorrect specs caused you.

 

Thanks for all of the info!

 

So I haven’t ordered the AFR sensors. I wanted to check the fuel pressure first. I did check all of the spark plugs. They were all the same, good electrodes, white ground/side electrodes which I believe indicate lean condition.

I checked the fuel pressure by installing a tee on the quick disconnect fuel line before the rail. the fuel pressure reads 30 at idle, and 30 at 2500 rpm. I think that is too low but can someone please confirm? As a reminder, I have the 4.0 v6. I think my issue is the fuel pump. Even though the code is for one bank, the live data shows both banks running lean.

 

I can't check for your specific vehicle until I'm back at work tomorrow...but the tundra/sequoia v8 has a fuel pressure spec of 38-44 psi. I would imagine the v6 to be similar but I can't say for sure, yet.

30psi is the low end for port fuel injection. So it's not out of the realm of possibility. I'll check tomorrow.

 

Mine is saying 40.8 to 41.7psi for fuel pressure. Which is also what I found with a google search. https://www.purefjcruiser.com/docs/...rvice Specifications/1GR-FE Fuel/00300410.pdf

BUT, that pressure is only valid when selecting the fuel pressure test via a scan tool. The fuel pump has a low power and high power mode, so I bet this test sets the fuel pump to run in high power mode.

Because of that, I don't think your 30psi reading is a valid number to compare to the 40.8 to 41.7psi spec.

You might be able to bypass the fuel pump resistor to mimic this test. Though I have no experience with that. See this post for more info on how the fuel pump works. https://www.4x4community.co.za/foru...1b28d754bb7650d51e1c751&p=3810410#post3810410

 

I forget what the pressure regulator is set to, but I do remember seeing on here where at leat one person was in the low-mid 20s while driving highway speeds, they were toggling between 25 for low and 35 for hi modes, with zero misfires.

As long as I was north of 25-30psi with any EFI engine at idle, consistent, after the regulator, I'd be content. I'm not familiar with the two different V6 used in these trucks to say more than that.

 

Thank you! I tested fuel pressure before the regulator. I do see mention of "connect intelligent tester, select Diagnosis/Active Test/Fuel Pump, standard pressure 40.8-41.7 PSI." That is annoying that I need a scan tool just to check fuel pressure. However, the next step is to "disconnect the tester, start the engine, standard pressure 40.8-41.7". Since there is a step without the scan tool, I am thinking maybe not necessary to check fuel pressure?

 

I guess one option would be to rev it up to 3000 RPM to get the fuel pump to switch to stage 2, and read the fuel pressure gauge?

 

I finally got around to bypassing the fuel pump resistor, and fuel pressure was 40 PSI. So seems the fuel pump is not the problem. I am noticing the surging under 1/2 - 3/4 acceleration, is that consistent with AFR sensors needing replaced? Or more likely MAF sensor, vacuum leak, or something else? Thanks

 

@Sbenecki, did you ever get this figured out?

 

bypassing the fuel pump resistor fixed the issue, and I just left it like that. So I assume the underlying issue is the fuel pump or the related resistors/modules.

 

I read thay as a clogged fuel filter, as a long retired AUDI tech above +11 you pretty damn lean. You should be -8/+11 ( +11 being your running 12.1-8) AFR OR approaching lean

 

I would need you to send me live logs, apologizes did not read whole thread. Could be wiring issue , broken wire but you should have burned a plug or piston by now.