Just when I thought I had this problem fixed it pops up again! To reiterate. I had this problem come up a couple moths ago. Thanks to many suggestions on this forum I did a smoke test and located an air leak in the plastic intake tube. I repaired that leak observed the live data which confirmed the fix. I then reset the Long term fuel trims. Everything was fine for weeks. Now the p0171 code pops up again! So I pull out my trusty smoke machine and do another test of the intake pipe. No leaks. I then put the nozzle in the oil fill hole. No leaks in the PVC system. I can now say with confidence there is no air or vacuum leak. The live data from my Foxwell scanner shows LTFT for bank 1 at 10.2 and LTFT for bank 2 at 8.4. I believe 10 is limit for the CEL so I am .2 over the limit for bank 1.(prior to fixing the intake leak my LTFT were 14 - 18).

Can anyone suggest the next steps. BTW, I have already changed the fuel filter and the MAF is only a year old and I have cleaned it...twice! Since my problem is bank 1 the problem has to be something unique to that bank.

 

I think the limit for the CEL is 25, or is that when RESTRICTED PERFORMANCE is displayed?

 

It can't be 25 that because in addition to CEL I get restricted performance that goes away after a few miles

 

What are your short term trims doing? You need to add them together to see the total fuel the car is adding. Also do you happen to still have your old MAF? If so I would swap it to see what happens.

Finally go and get your emissions checked somewhere and see if the tailpipe lambda readings match what the car thinks it's doing.

 

If it's an air leak the trims should drop much nearer to zero if you rev for a short time to 2500 or so.

Do they?

 

FWIW, In my case, an extremely small leak in the part load breather circuit would set a P0171 code.

 

Codes P0171/P0174 come on when the sum total of the Long-term and Short-Term trims reaches 25. It means that the ECU has to add 25% more fuel than what the base table says it should be.

Remember, a trim is not a simple number "for the engine" or "for the bank", it is really the "elevation" on a 3-D map of Load and RPM. IOW, there was a time while operating your car with a certain load on the engine, and at a certain RPM, the short and long term trims at that load/rpm added up to 25. You might be able to read the "freeze frame" data to see what the parameters were when the fault was logged.

Normally, checking the trims a idle gives you the best hints if the base problem is air leaks. This is because idle is high vacuum and the proportion of leak to metered air is higher. IOW, air leaks manifest with high trims at idle.

The trim logic applies outside of idle of course. Normally, once the air leaks are fixed, high trims outside of idle point to faulty/dirty/incorrect air flow meter. IOW, if the incoming air is measured wrong, the trim logic can "correct it" to a degree, but you can run out of adjustments at some point.

If you are in maintenance mode and you want to get this right, you need to aim for low trims (like, say 5%). Higher trims make the engine a lot less fun to use. It is not terribly responsive to throttle input, pinging noises can develop. IOW, you can definitely tell if you are driving an engine with high trims (even if well below 25% and there are no codes).

Best of luck, keep us posted.

PS: in the most edge case I have seen, air leaks were created by opening cracks in the intake during acceleration. The engine was rocking on its less-than-perfect mounts and air leaks developed. There was no detecting this with engine off with a smoke detector...