P0171 and P0174 lean codes

[Magnum65]

Hi all,
2012 VE series II Commodore z series wagon.
Am very frustrated with my engine light coming on for a few days then going off for a few days over the last six months. The mechanics suggested to replace the fuel pump but could not guarantee this would fix the problem and suggested I take it to an auto electrician. The auto electrician did a smoke test and said it was the electronic vacuum pump for the brakes. Replaced it with a secondhand unit because they thought a new one was too much. Engine light comes back on a few days later! Left it with them for another day but they didn't get around to look at it. It seems it's in the too hard basket.
Today I bought a OBDII scanner an confirmed the codes. LTFTRM is >20%, fuel pressure at idle around 340 kPa, O2 sensor voltage max at 1.25V low ~0.05V.
Cleaned MAF sensor and checked for leaks and added fuel system cleaner. Have cleared codes and see how it goes in the coming days, but need to drive 4000km in a week.
Any suggestions would be appreciated.

 

[monstar]

I realise it is a VE, but it would help to know what is the engine, a V8? The fuel pump idle duty idles 49psi vs 58psi for start.

 

[Magnum65]

The engine is a V6 3L with 220,000 km.

 

[mantaray56]

Long term fuel trim @ 20% is way too high, your car has been running lean for a while.
Check put this video for an idea what is going on. It may save you money in diagnostics fees.

 

[Magnum65]

Have watched some youtube videos, LTFTRM increases with revs which suggests fuel rather than air leak. Fuel pressure drops just below 300kPa when rev'd in Park (not under load). Does this sound about right. I drive 200km to and from work each day on weekdays and engine seems fine. Bank 2 seems to fault first but bank 1 is also high >20%. I've read swapping fuel pump is a real pain so not happening before my trip to SA from Sydney. Should I risk it as it's got me to work for over six months? My wife will be with me on the trip, so if the car breaks down all hell will be upon me!

 

[greenacc]

At around those ks my O2 sensors started playing up and so did my original ignition coils.
Just food for thought.

 

[blackve76]

What he said

At around those ks my O2 sensors started playing up and so did my original ignition coils.
Just food for thought.

Do 02 sensors

 

[Magnum65]

Today I compared our other ve commodore.... I know DOH. Too focused on my cars problem and overlooked comparing the readings to my wife's 2011 ve!
Anyway I noticed the following:
1. On the scanner the PID info is different, 2011 has more info on my scanner, Bosch 1110
2. MAF readings a bit different. My car baro pressure 101.0, hers 102.0. MAF idle mine 4.35 hers 4.7 units ??
3. MAP a little different but not too much
4. O2 sensors seemed a bit different but hard to tell
5. fuel pressure both around 400 kPa at idle, mine 400 at 3000rpm, hers ~300 at 3000 RPM. But fluctuate a bit.
Planning on getting a new MAF sensor and upstream O2 sensors tomorrow and fitting tomorrow night. Does this sound like the best way forward?
Bank 2 O2 sensor looks a bit awkward, any tips?
My wife's car has bad brake shudder so hesitant to take that to SA.
Cheers

 

[greenacc]

Those O2 sensors can be bloody tight. Make sure you have a good quality sensor socket or other tool and a good grip before you start pulling or you might round them off and get into trouble.

 

[Sean880]

5. fuel pressure both around 400 kPa at idle, mine 400 at 3000rpm, hers ~300 at 3000 RPM. But fluctuate a bit.
Planning on getting a new MAF sensor and upstream O2 sensors tomorrow and fitting tomorrow night. Does this sound like the best way forward?
Bank 2 O2 sensor looks a bit awkward, any tips?
My wife's car has bad brake shudder so hesitant to take that to SA.
Cheers

From what you have said you have both bank 1 and bank 2 reading about +20 % LTFT and you have confirmed no vacuum leaks.
I would not be replacing the upstream 02 sensors because there is every indication that they are both functioning normally. In any event your scan tool can be used to check that the sensors are oscillating normally. I fully expect the sensors would also have been checked by the guys that looked at your car previously. So I would not go replacing them yet. So many people go replacing the O2 sensors when the P0171/P0174 lean codes come up and then wonder why the problem has not been fixed because the lean codes are still there.

If the scan tool is showing the LTFT increasing about the same % as you increase RPM on both banks then the most logical cause would appear to be:

1. The MAF is still dirty or is faulty and is significantly under reading the volume of air entering the intake. As you increase RPM the 02 sensors on both banks will pick up the excess oxygen in the exhaust and the computer will begin adding fuel to compensate. The fuel trims will increase as the RPM increases from idle and even more air enters the intake.

OR

2. You have a fuel delivery problem that is affecting both cylinder banks fairly equally

An upstream exhaust leak on both banks, so that air is entering the exhaust pipes ahead of the 02 sensors, will also result in the 02 sensors recording a lean condition but I doubt this is an issue on your engine.

I would start with either giving the MAF a more through clean and check the results or replace it with a new one and check the results with the scanner.. If that does not rectify the lean condition on both banks then you can pretty much expect you have a fuel delivery problem given the symptoms and LTFT results, the cause of which needs to be investigated. You will need to check fuel pressure but I would not be rushing to change the fuel pump only to find out later that the real cause was partially blocked injectors on both banks that simply were unable to deliver the correct volume of fuel compared with their normal sound operating status.