P0171/P0174 Help!

does it run ok? did you do a fuel pressure check? It is possible to have a bad fuel pump right off the shelf. I came across these things on the web. This info is for Ford but I don't think GM would be much different. P0171 - System Too Lean (Bank 1) P0174 - System Too Lean (Bank 2) The Adaptive Fuel Strategy continuously monitors fuel delivery hardware. The code is set when the adaptive fuel tables reach a rich calibrated limit. Fuel System: · Contaminated fuel injectors · Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions) · Vapor recovery system (VMV) Induction System: · MAF contamination · Air leaks between the MAF and throttle body · Vacuum leaks · PCV system concern · Improperly seated engine oil dipstick EGR System: · Leaking gasket · Stuck EGR valve · Leaking diaphragm or EVR Base Engine: · Exhaust leaks before or near the HO2S · Secondary air concern Powertrain Control System: · PCM concern

Any common items when the code is set? Something like the codes set when your driving uphill, or only after you fill up at a particular gas station? Only when the A/C is on while going uphill?

I take it the codes have set after you replaced the FPR? What is the running fuel pressure and how is the flow rate from the new pump?

No hills in this part of TX. I've not noticed and correlation to a particular situation, most driving here is level 70 mph or so with A/C on.

They've set and pending set in the ~40 miles since the FPR change. I've not tested the flow rate. The pressure runs about 55psi at idle and will peak up to around 65psi when you blip the throttle and the change in vacuum boosts the pressure.

Thanks

Are you certain that the fuel trims for -both- banks are positive? (not one positive and one negative?) Have you tried cleaning the mass airflow sensor? Fuel filter? Disconnected and plugged the PCV and vent and checked for vacuum leaks between the intake manifold and crankcase? Any coolant loss?

Yes, that freeze data is correct, and consistent with the freeze data from other times the codes have set (always both P0171 and P0174).

Yes.

Replaced last pump replacement. Tank spotless, pump screen near spotless (and replaced), FPR screen spotless, pretty unlikely anything is clogged.

No, but the upper IM has new gaskets now.

No.

~199,500 miles BTW, all on M1 synthetic.

After erasing the previous codes and logging another 140 miles or so, I have yet another set of P0171/P0174 set and another pending set. New freeze data is as follows:

Closed loop / closed loop Calc. load 10.1% Coolant temp 172F ST1 17.9% LT1 24.9% ST2 21.0% LT2 24.9% MAP 17.1 in/hg RPM 1489 MPH 28 MAF 3.875 lb/min TPS 12.9%

Well, the upper IM was just off and now has new gaskets.

What is the fuel pressure during these conditions (simulate the freeze frame)?

Can you get the MAF reading at whatever is the safest maximum RPM for that engine at WOT?

Does your scan tool support graphing?

In my opinion, the folks that sold you the scanner are laughing all the way to the bank along with the mechanics that live in your area.

I think those things are sucker tools.....

Does the vehicle run OK or not?

I mean it's over ten years old and the mini pins on all the sensors only pass computer signals which means tons of intermittent failures 'show' on these foolish tools without meaning squat as far as running goes.

A good spray with an electronic contact cleaner on all the plugs and sockets for the sensors on an old vehicle can do wonders for them.

They 'really' are a 'sucker tool' you know....

Just my $0.02,

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 'New' frame in the works for '08. Some Canadian Bush Trip and Build Photos:

Not sure I have a way to simulate a load. I also don't have a "real" scan tool to read parameters in real time. All I have is the "good" Harbor Freight CAN / OBD2 scanner that displays / clears codes and displays associated freeze data. I do have a friend with a real scanner (Snap-On I believe), so perhaps I can get a test plan together and visit him.

Well, the scanner was very cheap and does quite well within it's limits. It displays and clears codes and displays associated freeze frame data, which I think is worth the $60 or so I paid for it.

As for mechanics in my area, after several years of searching for a good one, I concluded they all work for race teams, so I DIY everything.

I could see an intermittent connection causing a stray code, but this is a consistent issue and clearly shown in both the short and long term fuel trim values.

As for how the truck is running, generally ok, but I haven't pulled a heavy load in the past couple months, so I'm not sure how it would do at more than 20% load.

As for age, I'm no longer in the rust belt, I have much better shop space and it's a 3500 dually, so it doesn't wear all that fast in the mostly light service it gets. I have no plans to replace it any time soon. The gas savings calculator on edmunds.com says trading it for a hybrid would save me money in 54 years, my calculation was more like 25 years, but clearly there is no good reason to replace it.

Don't need to. Test drive it like you stole it, set the Snap-On scanner in 'movie' mode, floor it in first gear and when it shifts to second, hit the trigger on the scanner, review the movie near frame "0" forward and backwards frame by frame until you find the max RPM, then scroll to the MAF sensor and read the grams per second. With RPM, engine size and a few other ambient details, I can calculate whether the theoretical volumetric efficiency matches what the PCM PID are reporting. I'm leaning towards three things; either the MAF sensor isn't reading correctly or you have plugged injectors or your fuel pump can't keep up.

44-45 percent fuel correction is HUGE, there is a real problem there and you'd best fix it before there's collateral damage.

That's not a scan tool. In my business, that's an invitation to frustration.

Woa there, "when it shifts to second"??? What do you think I am, some kinda wuss? I only drive trucks with real transmissions :) (NP4500 in this case). Heck, one of the reason I keep getting bigger trucks is my hatred of automatics.

Well, it's on the third or is it fourth fuel pump. Since the problem has existed over at least two pumps I'm inclined to think it's probably not the pump.

The fuel injectors were replaced some 130k ago or so, at the same time the cats were replaced under warranty (also replaced all four HO2S). The facts that I always get both 171 and 174, all the recently pulled plugs were consistent, and the tank and FPR screens were all spotless leans me away from a fuel injector problem.

The MAF, well, that's original, now with 199,500+ miles of use on it. I did clean it with CRC MAF cleaner, though there was no sign of any visible dirt on it.

I've certainly been trying to locate and fix it.

It's a step above a basic code reader at least. I may need to invest in something better, perhaps PC based, got any suggestions for something good, but less $$$ than pro stuff?

Okay, when YOU shift to second.

Doesn't mean it's not fuel pump related. These things are well known for overheated harnesses in the tank and where the FP module plugs in.

Still doesn't lean me away from an injector problem. The PCM is still able to compensate for the lean condition, that's what the fuel trim numbers indicate, so it's not unusual that the plug color looks okay.

Two ways to tell if it's functioning properly, take the measurements and do the calculations or replace it with a new (not different) one.

Autoenginuity.

You can get into the enhanced GM package for about $400 The interface sucks but isn't as bad as some, It graphs, does mode 6 conversion without any hexdecimal conversions, does cam offset relearn, has bi-directional control, it is as close to a Tech 2 as you can get without spending $6K. On a laptop platform, it's not as easy to manipulate while driving as a dedicated scan tool. Or, buy a Snap-On scanner off of e-bay, they're pretty low on resale.

Sounds like a big vacuum leak common to both banks. Can you do a propane test? HTH, Ben

The last replacement, I replaced the hanger assembly as well.

You think it would be that consistent to always be both banks? I guess I could try the injector balance test if I get my friend over with the real scanner.

Ok, sounds like I need the real scanner again.

Ok, thanks.

i think your fuel pressure numbers are too low. possibly a bad fuel pump. I have heard that these numbers are correct. 60 to 66 psi. It should maintain 55 to 60 psi for ten to fifteen minutes with the key off.