03 Envoy XL -- Bank 1 & 2 System Too Lean

[dciolek]

Thanks for the link -- now if only I can figure out how to get to the connectors (from the top or bottom), I'll actually replace them...

I captured some data from the scan tool. The upstream O2 sensors are jumping all over the place -- but the downstream sensors are constant. This is all at idle speed with time in seconds at approximately 0.9 s intervals.

TIME 0 0.9 1.8 2.7 3.5 4.4 5.3 6.1 7 7.9

ABSLT TPS % 9 9 9 9 9 9 9 9 9 9
ENG SPEED RPM 547 552 547 556 557 557 548 551 558 563
CALC LOAD % 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9
MAF FLOW GR/SE 5.24 5.34 5.32 5.33 5.34 5.21 5.32 5.2 5.32 5.17
MAP KPA 34 34 35 35 35 34 35 34 35 34
COOLANT �F 181 183 183 183 183 183 183 183 183 183
IAT �F 66 66 66 66 66 66 66 66 66 66
IGN ADVANCE DE 18.5 18.5 16.5 20.5 19.5 18 16.5 17.5 17.5 18
ST FTRM1 % 0.8 0 0 0.7 0.7 0 0 0.8 0.7 0.7
LT FTRM1 % 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3
ST FTRM2 % 1.5 0.7 4.6 2.3 4.6 3.1 3.9 0.7 1.5 3.1
LT FTRM2 % 0.8 0.8 0.8 0.8 0.8 0 0 0 0 0
VEH SPEED MPH 0 0 0 0 0 0 0 0 0 0
O2S11 V 0.105 0.795 0.065 0.2 0.5 0.685 0.705 0.335 0.59 0.775
ST FTRM11 % 0.7 0.8 2.3 0 1.5 0.8 0.8 0 0 0.8
O2S12 V 0.805 0.805 0.805 0.805 0.81 0.82 0.815 0.815 0.825 0.82
O2S21 V 0.055 0.05 0.695 0.075 0.18 0.835 0.83 0.065 0.17 0.075
ST FTRM21 % 3.9 2.3 2.3 3.9 4.6 0.7 0.7 2.3 1.5 3.1
O2S22 V 0.85 0.85 0.845 0.84 0.845 0.84 0.835 0.835 0.835 0.83


TIME 8.7 9.6 10.5 11.3 12.2 13 13.9 14.8 15.7 16.5

ABSLT TPS % 9 9 9 9 9 9 9 9 9 9
ENG SPEED RPM 531 539 547 557 542 541 541 543 547 541
CALC LOAD % 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9
MAF FLOW GR/SE 5.3 5.3 5.28 5.28 5.29 5.28 5.29 5.27 5.28 5.26
MAP KPA 35 35 35 34 35 34 35 35 35 35
COOLANT �F 183 183 183 183 183 183 183 183 183 183
IAT �F 66 66 66 66 66 66 66 66 66 66
IGN ADVANCE DE 14.5 19.5 19 17.5 17.5 17 17.5 20 16.5 17.5
ST FTRM1 % 1.5 1.5 0 -1 2.3 2.3 1.5 2.3 2.3 2.3
LT FTRM1 % 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3
ST FTRM2 % 3.1 1.5 3.9 0 3.1 0.7 3.9 3.9 2.3 3.9
LT FTRM2 % 0 0 0 0 0 0 0 0 0 0
VEH SPEED MPH 0 0 0 0 0 0 0 0 0 0
O2S11 V 0.565 0.075 0.075 0.075 0.82 0.835 0.085 0.065 0.065 0.095
ST FTRM11 % 0.7 1.5 2.3 0.7 0.8 0 3.1 2.3 2.3 3.1
O2S12 V 0.82 0.825 0.82 0.82 0.82 0.815 0.815 0.81 0.81 0.81
O2S21 V 0.13 0.235 0.85 0.08 0.815 0.065 0.815 0.8 0.835 0.505
ST FTRM21 % 3.9 3.9 2.3 2.3 0.7 3.1 1.5 1.5 0.7 2.3
O2S22 V 0.83 0.83 0.825 0.82 0.815 0.82 0.82 0.815 0.815 0.81


TIME 17.4 18.3 19.1 20 20.9 21.7 22.6 23.5 24.3 25.2

ABSLT TPS % 9 9 9.4 9.4 9 9.4 9 9 9 9
ENG SPEED RPM 547 548 558 547 543 549 537 537 558 542
CALC LOAD % 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9 1.9
MAF FLOW GR/SE 5.27 5.35 5.23 5.38 5.26 5.36 5.25 5.24 5.25 5.15
MAP KPA 35 35 34 35 35 35 34 34 34 34
COOLANT �F 183 183 183 183 183 183 183 183 183 183
IAT �F 66 66 66 66 66 64 64 64 64 64
IGN ADVANCE DE 20 17 19.5 17 17.5 16 17.5 20.5 14.5 19
ST FTRM1 % 0.8 0 0 2.3 0.7 0.8 1.5 0.7 -3.4 -7.5
LT FTRM1 % 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 9.3 7.8
ST FTRM2 % 3.1 2.3 2.3 1.5 0.7 3.1 3.1 0.7 -2.2 -6.3
LT FTRM2 % 0 0 0 0 0 0 0 9.3 9.3 7.8
VEH SPEED MPH 0 0 0 0 0 0 0 0 0 0
O2S11 V 0.07 0.065 0.27 0.865 0.2 0.085 0.095 0.81 0.91 0.735
ST FTRM11 % 0.7 0.7 1.5 0 0.8 0.7 2.3 0 -4.6 -7.7
O2S12 V 0.805 0.805 0.805 0.805 0.805 0.81 0.805 0.805 0.835 0.855
O2S21 V 0.835 0.44 0.1 0.145 0.115 0.515 0.385 0.91 0.91 0.77
ST FTRM21 % 1.5 1.5 3.9 3.1 3.1 1.5 2.3 0 -4.6 -7.7
O2S22 V 0.815 0.81 0.81 0.81 0.805 0.805 0.805 0.81 0.865 0.895

[dciolek]

Here is the full story so far tracking what I have done against suggested problems with DTC P0171 and P0174:


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
1. Ran fuel injector cleaner in one tank of gas
2. Ran fuel system cleaner (injector, intake, system) in one tank of gas
3. Ran ½ can Seafoam in one tank of gas
• Low fuel pressure or running out of fuel (fuel pump, filter, fuel supply line restrictions)
1. Changed fuel filter
2. Measured fuel rail pressure at idle (46 psi) and at high RPM (46 psi) and max pressure without engine running (3 on/off fuel pump prime cycles – 52 psi)
3. DID NOT CHECK YET: Change fuel pump or check fuel tank screen
4. DON’T KNOW HOW TO CHECK: Check fuel supply lines for restriction
• Vapor recovery system (VMV)
1. DON’T KNOW HOW TO CHECK

Induction System:
• MAF contamination
1. Used MAF cleaner/spray on MAF sensor
2. Reseated and tightened clamps at entry and exit to MAF and air filter box
• Air leaks between the MAF and throttle body
1. Did backyard smoke test with cigar through brake booster hose with air filter box cut off, did not detect any leaks
• Vacuum leaks
1. Did backyard smoke test with cigar through brake booster hose with air filter box cut off, did not detect any leaks
• PCV system concern
1. No PCV system on the Envoy XL 2003
• Improperly seated engine oil dipstick
1. Unlocked and reseated oil dipstick when adding Seafoam. Performed oil change 75 miles afterwards.
 
EGR System:
• Leaking gasket
1. DID NOT CHECK YET
• Stuck EGR valve
1. DID NOT CHECK YET
• Leaking diaphragm or EVR
1. DID NOT CHECK YET

Base Engine:
• Exhaust leaks before or near the HO2S
1. DID NOT CHECK YET
• Secondary air concern
1. DON’T KNOW HOW TO CHECK (Maybe Manifold Pressure?)

Powertrain Control System:
• PCM concern
1. DID NOT DO YET: Perform Hard Reset after replacing O2 sensors

OTHER ITEMS PERFORMED:
1. Did Seafoam engine treatment in vacuum line – ran hard to burn off contaminants
2. Added Seafoam to oil and then changed oil and filter after driving 75 miles
3. DID NOT DO YET: Change upstream oxygen sensors
4. DID NOT DO YET: Change downstream oxygen sensors
5. DID NOT DO YET: Check fuel pressure at tank if there is another Schrader valve

SYMPTOMS:
1. SES light and DTC P0171 and P0174
2. Hard time completing a drive cycle
3. Rough idle
4. Low fuel rail pressure
5. Poor gas mileage
6. Downstream H2oS always high “Rich” value (both above .8 continuously)
7. Long Term Fuel Trim Bank 1 staying at positive 2.3% value
8. Mostly positive Fuel Trim values on both ST and LT - rarely go negative

[danielsatur]

Is your son learning any of this stuff?
What's in common with both banks?
Air/fuel

Air- both banks running lean.
Unmeter Air leaks - Smoke Test Passed
New unstream H02 sensors for Air/fuel mix.
Cleaned MAF/IACT sensor, but are they good?
Do a Google ''Symptoms of bad MAF sensor''

Fuel pressure?

[dciolek]

Well, I know when I'm beat. Three fresh attempts to get to those upstream o2 sensor connectors from both above and below and I'm convinced there is no way to do it without disconnecting some major component like a drive shaft or the entire exhaust system (well beyond me in the excitement category).

Gonna make my way to the stealership and let them put the o2 sensors in and maybe even get the fuel pump done (in that order).

Thanks for all your help and encouragement -- learned a lot along the way (especially with the smoke test and about fuel systems/sensors).

[danielsatur]

Stealership - You said it! $150hr

How about a local muffler shop?
They can do a catalytic converter back pressure test, install the upstream H02 sensors, look for leaks, and replace any bad rubber exhaust mounts.

[dciolek]

Good point. I was thinking taking it to a GM dealership because I had read a technical service bulletin dating back to 2006 that said P0171 and P0174 were being caused by dirty injectors. They had a "proprietary" injector cleaning solution identified (GM cleaner and special tools to run the cleaner through the system) as a "fix".

Thought maybe that might work better than my injector cleaner, fuel system cleaner and Seafoam treatment (but maybe not). I might do that AFTER the steps you suggest above instead. Here is why...

I have been reading up a bit on the o2 sensors. It says that the downstream sensors should be settling in to an average voltage of about .45 if they are working correctly and your catalytic converter is working correctly, even though the upstream sensors should be jumping around from high to low (crossing the .45 several times a second between like .2 and .8) as the engine keeps things running properly for a fuel injected system.

So, with the scanner tool and the frame capture (or even just looking at the data live) -- I can see that the upstream sensors are doing just that -- jumping from low to high constantly. But I can also see that the downstream sensors are ALWAYS high (.68 at one test run highway speeds and .8 at another test run at idle). High sensor readings indicate a RICH condition.

If this were in the UPSTREAM sensors -- it would instruct the computer to lean up the fuel delivery to bring the condition back towards .45. I suppose if it was constantly doing this outside of norm values, then it would eventually set the P0171 and P0174. But I'm not sure what this means in the DOWNSTREAM sensors (as far as what the computer is telling the car to do to modify the air/fuel mix). I am getting a Long Term Fuel Trim reading on both banks at highway speeds at about positive 7%. The positive means LEAN condition - so engine, add more fuel (again matching the P0171 and P0174 banks to lean). However this seems opposite of what the downstream sensors are telling me (your exhaust gas is too RICH).

The downstream sensors are used to monitor if the catalytic converter is doing its job. So if the downstream is matching what the upstream is doing -- then the converter isn't working and the exhaust isn't being modified to remove pollutants.

BUT, the downstream sensor in a well functioning car should be settling in at about .45 volts (the ideal fuel/air ratio). So, the way I see it -- the downstream reading constantly high might mean that the converter is doing its job "somewhat" (because it is not matching the same voltages as the upstream -- so it IS changing the exhaust fuel/air ratio when passing through the converter). But maybe it is either not doing it well enough (bad cat), or it is constantly being fed an "average" stream before the converter that is TOO RICH and can only flatten it out somewhat to an average RICH condition.

So -- this leads me to the same place you suggested (in a long winded way I have to work out, because I want to know WHY, not just WHAT).

I should replace the o2 sensors in case they are either biased or not responding FAST enough(although I know the upstream ones ARE reacting because they are going low to high within good ranges) . Or I can check to see if there is an exhaust restriction (back pressure test) or problem with the catalytic converter (not sure bout that one).

If there were a leak in the exhaust system between O2 sensors -- the downstream would tend to read LEAN rather than RICH (right?).

And why are the banks LEAN but the downstream sensors RICH (unless both sensors are bad to the exact same extent, which seems a little far fetched).

Still on the path, but I will be engaging some shop help at this point...

[danielsatur]

I would cut H02 wires, splice, soldering, and use electrical tape for fix!
2-wires are for the heater, the other 2 for the sensor.

[dciolek]

Didn't think about the splicing...

...if the part wasn't so damn expensive I'd be game. What if the wires aren't the same colors across manufacturers and I hook the wrong ones - blam, you fry the good sensor.

Sounds like a fun game to play though. You could always recover from it if it didn't work by just unplugging at the normal connector spot I suppose, just need to buy a new sensor.

[dciolek]

Taking it in for an $80 smoke test this weekend. I called to ask about the labor cost to install the sensors and they won't install my parts (looking for an independent mechanic to do this now). Their part cost was 2.5 times what I paid for premium Bosch sensors.

Shop labor PER sensor for the upstreams was quoted at 3.7 hours (I confirmed this on Repairpal).

What they heck do you have to disassemble to get to those connectors that will take 3.7 hours? Does anyone have access to an Envoy shop repair manual that gives a sequence for the deinstall/reinstall of the o2 sensors on a 2003 Envoy XL 4WD 5.3 engine?

[danielsatur]

Check with http://www.alldata.com , Ask a local muffler shop how long doe's it take?

[dciolek]

That was the local muffler shop's time quote!

They said 3.7 hours -- the online Repairpal (I am assuming they show the same information you get from alldata.com -- I used to subscribe there too) quoted labor was 3.8 hours on the low end.

I'm going another route taking it to a local mechanic recommended to me that has a full time shop job during the day and takes in cars at night. I can buy the parts and he thinks he can get all four changed in an evening so it should be a bit better cost wise than full shop rates. We'll see...

[danielsatur]

Originally Posted by danielsatur

I would cut H02 wires, splice, soldering, and use electrical tape for fix!

2-wires are for the heater, the other 2 for the sensor.

Look for color coded wires!

All H02 sensors are the same except for the wire length, and connectors.

The heater signals are usually the same color, and should measure a resistance like a heating element.

[dciolek]

Well - I didn't trust my smoke test, so just spent $90 and had one professionally done.

It passed the smoke test with no vacuum leaks or injector seals found to have problems...

On to the O2 sensors!

[danielsatur]

I glad it passed the smoke test, that tell's me you did a good job doing your own test.
LOL - I think a good cubin cigar $80.
It's always good to have a second opinion.
Did the Technician feel like the HO2 sensors were bad too?
H20 sensors, but how much is it going to cost to put them in?
MAF ?
Fuel pressure?

[jong22250]

i have the same truck v8 and all i chased this code since i did the tune up in june till dec put 4 o2 in it fuel pump intake manafold gasket finaly i got some where i asked friend of mine who is a tech to look at it he pulled one plug and screwed it back in and said he never had a gm with out a egr valve run a bosch plug u running bosh? i changed the plugs ac delco platnums 50 bucks for 8 and poof codes gone 2500 miles no codes he told me the electroid is so small on the bosh it does not complety burn all the fuel then u got unburnt fuel in the cats confusing the o2 sensors , oh and there is a pcv valve it is on the drivers side in the back by the fire wall intop of the valve cover one other thing pass side upstream o2 if u reach through the fender well on top of the frame u can get ur hand back in there and get to that o2 plug it took me a freaking hour to change it put u can get to it with out droping any parts