With the engine RPMs steady, I think the STFT should be fairly consistent. It fluctuates some, but not sure why it would be bouncing around between -10/+10. But +40 on the LTFT is a lot. I take it the trims are about the same on both banks, correct? If you hold it steady at higher RPMS for a while - like maybe 1500-2500 - does it start to come down? If the fuel trim starts to come back down to earth with higher RPMs (lower vacuum), that would point to a vacuum leak.

I agree its odd that the errors show up after fitting the new pump, which is why I might try resetting engine/fuel adaptations first. The car might have stored adaptations based on the delivery from the weak pump and now needs to recalibrate. Logically, you would expect rich codes when readjusting to a stronger pump…but who knows. Can’t really think of any other reason why a new flange/pump would resolve the low pressure code but cause new lean codes.

 

LTFT sits around +40 regardless of RPM (drops slightly when increasing throttle but levels out to 40 again). This time STFT sat at 0 at idle but dropped to -20 when apply throttle.

I've not done an adaptation reset yet, though driven nearly 1K miles in the past 2 weeks.

 

So your total fuel trim is dropping by about 20 when applying throttle. That seems to suggest a vacuum leak - pretty big one at that. For reference, I had a valve cover breather come loose once - didn’t have it clipped in properly when I replaced the air intake. So it was effectively just a big hole in the air intake. That gave me fuel trims in the 40+ range as I recall.

You said you previously tested the PCV - how did you test it? Usually that’s a replacement only item because when you pop the old cap off to check the diaphragm, the brittle tabs on the cap usually break off so you need to just replace it.

Looks like you also replaced the motor mounts yourself when you did the fuel tank. I haven’t done that job, so I don’t know exactly whats involved. Wondering if something might have popped off in the process - maybe a breather or one of the vacuum lines that runs along the passenger side.

 

Bank 1 & 2 DTCs persist regardless of ambient temps or driving styles. Finally managed a vacuum leak test at the main dealer and was confirmed NO leaks. Also whilst engine idle RPMs are still staying locked in where they're supposed to be, after being gone for some time, the rhythmic shudder has returned every time I fill up with fuel, regardless of fuel level at fill start or level at fill stop.

There's an old TSB from 2016, I think, for 02 sensor issues, software issues and emissions/fueling performance. It listed all 6 sensor part numbers for replacement.

Any thoughts on this?

 

Replaced all 6 O2 sensors (massive undertaking at nearly 8 hours) and now the MIL for bank 1 & 2 lean DTCs has become consistent. The code so far after 3 days have ONLY come on in the morning and in the exact same location and time from my home. This leads me to think perhaps this has something to do with a drive cycle and the ECU. I can multiple starts and stops all day long without once seeing the DTCs.

It is now being suggested perhaps the catalytic convertors are failing and when the ECU's performing its morning check routine it's picking up this data. There's also a faint brief rattle on acceleration.

 

You mention that you get a rhythmic shudder every time you re-fuel. It just seems like there has to be something wrong with either fuel delivery or EVAP system. This would also be consistent with lean codes on both banks. The dealer said no air leak, but did they check out the EVAP system?

When you re-fuel, I assume the engine is warm at that point. Does the rhythmic shudder happen if you just release the gas cap and close it back up without adding any fuel (again - warm engine)? Do you notice much hissing of air when you open gas cap? I also remember from a prior post that you had a gurgling noise in the tank when the engine was running. Is that noise still there? All of this stuff seems to point to the EVAP system, especially since you’ve already replaced the in-tank fuel pump.

Doesn’t seem to me that failing cats would cause these lean codes, but I guess its possible. My understanding is that the lean codes are set based on the lamda sensors that are ahead of the cats. Plus, you’d have to have both cats going at the same time.

The morning drive period might be related to a drive cycle - MILs will set once an existing code is confirmed on a drive cycle. I also wonder if that time period in the morning might correspond to the time it takes the car goes into closed loop fuel control, i.e., once the engine is to operating temp. Either way, I don’t think it rules out much.

 

No issues with fill up and NEVER overfill. Yes, when I open the gas cap SOMETIMES, not all of the time, there's a prolonged and loud hiss of releasing pressure but that seems to make little difference. Also I've tried partial fill ups from say half a tank to fill ups from empty and that makes no difference either.

Evap system was not tested recently but I think it was perhaps a year ago.

Upon further consideration, the tech does not believe it's a cats issue.

 

I ran the test routine in SDD and the system passed. Asked my tech mate and he said if the routine passed then there shouldn't be any evap faults else it would've said...

 

On day 4 decided to let the truck idle for 20 in the drive instead of driving off after warm up to see if perhaps the DTCs would happen after a certain amount of time and support my theory from the past 3 days. Well of course the MIL never illuminated, in fact it took 2 hours of mixed driving for it to illuminate and interestingly enough it came on 4 times on Tuesday, thus negating my theory, I think. However, Wednesday, yesterday and today it came on at the same spot/time as it did for those other 3 days.....so.....

This evening I parked for a fuel fill up and idle was normal as always. Opened the fill cap and no hissing of air but this time I was monitoring live data, RPM and fuel trims and idle went from normal to shuddering again with RPM going from 620 to 550 to 620 to 550 rhythmically and trims following the "wave", STFT -25 to -7 to - 25 to -7, etc and LTFT +43 to +41 to +43 to +41, and so on.

 

It’s an interesting problem. You seem to be running very lean all the time (prior post says fuel trims at +40), then when you take the gas cap off, you start running a little richer (although still looks pretty lean). Hate to beat a dead horse, but since no one else seems to be chiming in … I think there has to be something wrong on the EVAP side. Purge valve, charcoal canister, vent solenoid, or liquid/vapor separator. Since you already replaced the LP pump and fuel pressure sensor, I just can’t think of any other scenario that would cause that effect when you remove the gas cap.

Hopefully someone else might have other ideas.