Gentlemen, thank you for your response!

P73990-I also smoke tested the exhaust from the tips forward and saw nothing. New O2 sensors swapped fine no thread issues-stayed tight.

-I will put in the Denso MAF. There are MANY choices for "applicable" O2 sensors. Do you have a PN for a known good sensor, or is there enough variation at the manufacturer level it doesn't matter that much?

-I am in Mount Vernon, WA, USA

-Never had an EVAP system fault

-The ONLY codes I ever get are for the lean condition and always together. 171/174

I have checked the three one way valves in the vacuum/EVAP system and all stay shut and look to be facing the correct direction. All my plumbing is plastic except a few inches of rubber line from the fuel pressure sensor to the intake source nipple and the boost PRV to its intake source nipple. Both are fine. I have replaced the push-in fitting receptacle in the intake for the plastic line from the EVAP system. It does not leak.

-I understand that the short term values are for "live" corrections and long term values are for how the system has to adjust the short term to make the mix right. What I DON'T understand is HOW is does it, how long it takes for changes to take effect and exactly what I do that forces the system to make a correction. I have ideas, but they may not be (probably not) correct.

Gilbertd,

-I think I understand the relationship with the fuel pressure and PWM of the fuel injectors to compensate for low fuel pressure. Though I will not claim a great understanding of the system, I have read the manual a number of times to try my best. I know there are MANY sensors and a mountain of data the ECM looks at to make the needed calculations. That being said, the inter-relationship of the numerous systems vexes me. I just don't have that much experience yet, so I appreciate your input very much.

-The upstream O2 sensors in my system output a uA signal and the downstream 0-1V. Lean condition aside, they look to be responding appropriately.

-Fuel pressure seems low across the range, but it does go up with demand though I'm not certain it sufficient at any point since I can't see commanded pressure. This will cause the ECM to lengthen the FI PW to compensate. FI PW ranges from roughly 2.9 ms at idle to 9 ms up a steep hill at 3k RPM 2-3 PSI boost. STFT's up the same hill will switch +- 5-7% and LTFT's will drop to roughly 11-14% WITH B1 always being a smidge fatter. If I understand correctly, B1 is the far side, or end of the line so if fuel pressure is low, B1 will be affected the most.

-This is with the Echlin MAF. STFT's have never been constantly in the positive though LTFT's have. I will put in the Denso sensor and report back after Christmas.

-I am not sure exactly what will reset the fuel trims to zero. I have tried doing a full system module reset through SDD (which I think resets ALL adaptions?) and I tried LPGc's method of clearing all codes, unplugging one side of fuel injectors, running until the CEL comes on, resetting codes and immediately going for a drive so as to not let the system idle and foul of the readings. The STFT's always fluctuate within 6-7% +- and LTFT's always go right up to high teens and after a bit of driving peg in the low 20's during light acceleration and coasting, at which point STFT's go to 0.

-I will put in the Denso MAF and the new fuel pump once I have it and report back.

Thanks for adding your experience to my challenge!

Josh

First off, Sorry for invading your forum with a different vehicle, but I stumbled on a thread and member that I am really hoping can shed some knowledge on my issue, which I know is not new.

2006 L322 4.2 SC petrol (for you UK types)
I have SDD v 165 and iCarsoft LR V3.0 for scanning. HOWEVER, these two scanners seem to output file formats that are very difficult (at least for me) to export in a helpful format outside of the tool. If anyone is familiar with either, I'd love to know how to do so, as I have many data log files I've created while testing.

Testing I have done
-verified 5v reference and ground to MAF, both MAP's and fuel pressure sensor
-Verified a good looking switching signal for the upstream O2 sensors at +-.03 uA (did I get the decimal in the right spot?) and downstream sit right around .7v-.8v
-Fuel pressure hits low 60's after start up and drops to about 41-42.5 at idle in gear thereafter. This seems to be about 12% under the spec per the manual. Lots of speculation on whether this is low enough to cause my issue. Under a good load up a 16% grade at 3k rpm doesn't get it above 63 and I only see about 2-3 psi of boost, though the ECM is probably pulling boost via the PRV-which does not leak
-Barometric pressure sits right about 1 bar at all times
-MAP readings start at 4-6 PSI and never more than 18.
-KOEO the MAP sensor in the TB elbow reads 4.9v and the MAP sensor in the RH rear intake manifold reads 2.4v. Both sensors drop smoothly to about .6v as vacuum is applied by my MightyVac tool
-LTFT's --B1 seems to always be a few percent higher (positive) than B2. After startup they will be roughly B2-15% and B1-19%, but after a little driving both will come up to about 21-22% when under light throttle and coasting. Under load, roughly 1500 RPM and above will bring both down to 12-15%, load depending, maybe a tough lower, but never under 10% and never negative
-STFT's seem to always fluctuate back and forth from +-7% and usually settle around 0% often during light throttle and coasting. Load gets the most switching. This is with a new NAPA Echlin MAF sensor. I also have a Denso sensor that cost me $160 which I thought was the OEM replacement but that one gives more erratic readings, so maybe a dud? I currently have the NAPA sensor in. Suggestions for a know good brand?
-I have smoke tested, propane and carb cleaner blasted every connection and vacuum line in the engine bay to no avail. With SDD open looking at all fuel trims I saw no change. I have looked around the connections in the entire induction system from the MAF to the TB and all looks fine and tests fine-no leaks that I can find.
-The codes always come together, and reset after I do some checking of things and clear them after roughly 2-4 drive cycles when slowing for a roundabout and accelerating to go through, this is around 15-20 MPH.
-I have replaced the fuel pressure sensor with a good one that gives the same reading as the old one
-I have two new MAF's, and the NAPA version is currently installed
-I replaced the MAP sensor in the RH rear intake manifold because I thought the 2.4v resting voltage was suspect, but the new one reads the same as the old one and must be a 2 bar type?
-I wasn't sure about the upstream O2 readings so those are new OEM ones-Bosch, I think?
-Fuel filter is new
-Tank has been cleaned and system flows well I think
-SDD v165 has no provision for seeing commanded FP so not sure about that one
-I have inadvertently fired quite a few parts at this project, not blindly, but lack of proper understanding
-It starts immediately and runs great, does not hesitate or stumble really at all, only right after I have fiddled with something, after driving for a minute or two it smooths right out. Acceleration is decent, if not a bit sluggish from a start
-It seems very cold blooded-though I have watched the ECT readings deliberately and it comes up very regularly, just slowly. It seems to take about 6 miles of driving and maybe 10 minutes to hit operating temp and does not overheat-195 is where it lands.
-Testing is always done between a half and quarter tank
-I ran the SDD fuel/purge system leak test which passes
-All grounds in the engine bay and wheel wells have been removed and cleaned. I have also checked and cleaned all grounds in the front sill and kick panel areas, both sides. Wiring looks good everywhere.

I wish there were a vacuum leak to find. Any ideas? Every connection I took apart the o ring looked fine and was not plasticized. Oil filler neck does not seem to leak.

I have not checked wiring from the ECM connector to the sensors signal wires, but all looks acceptable and undisturbed externally. I know this is not a guarantee, but experience tells me it is likely not an issue. Looms and protection all seem to be intact.

I love this thing and can't quit on it.

Thanks for any help to an outsider (kinda)

Josh

(Initial PM to Lpgc, who suggested I repost here)
2006 L322 4.2 SC
This is a bit of a hail mary at this point. I have been troubleshooting (because I have no formal training, just the manual and SDD v165)the 2 lean codes 171/174 (only those) for about 2 months now. I have tried many things. Yesterday I stumbled on your replies to a gentleman with a nearly identical issue about 2 years ago. Would you be willing to give me some clues? If yes, what info do you need? Still newish to SDD and have trouble getting files out of it for others to view.

Thanks,

Josh