P0171 again, advice needed
Thread Starter
Instructor
Joined: Dec 2012
Posts: 191
Likes: 23
From: Louisville KY
P0171 again, advice needed
My new to me 03 Z is continuing to experience P0171HC codes.
It has done this intermittently since I bought it in Nov. I'm not sure if it means much but the car only has 7450 miles on it.
Recently I found the intake bolts lose and ended up replacing the intake seals which seemed to fix the problem for about 100 miles, now it’s back. I even switched positions with both of the #1 O2 sensors to see if the code changed banks, it did not. Along with the new intake seals the car has new plugs, Breathless Performance vortex air rammer, and long tube headers. I installed the headers and it was doing this before the header install, so I know they have nothing to do with it. Other than that it is stock. I suspect the previous owner had it semi-tuned, as the shift light is turned off and a Crane Cams Powermax came with the car.
I've searched for vacuum leaks and cannot find anything. For troubleshooting I have a Actron 9575 OBDII scanner and it shows the PID outputs in real time and a freeze frame of when the code was set, but I honestly do not know what I'm looking at.
The PO became ill and car sat for 12-18 months with very little to no operation, could the injectors be dirty?
Any help is much appreciated.
It has done this intermittently since I bought it in Nov. I'm not sure if it means much but the car only has 7450 miles on it.
Recently I found the intake bolts lose and ended up replacing the intake seals which seemed to fix the problem for about 100 miles, now it’s back. I even switched positions with both of the #1 O2 sensors to see if the code changed banks, it did not. Along with the new intake seals the car has new plugs, Breathless Performance vortex air rammer, and long tube headers. I installed the headers and it was doing this before the header install, so I know they have nothing to do with it. Other than that it is stock. I suspect the previous owner had it semi-tuned, as the shift light is turned off and a Crane Cams Powermax came with the car.
I've searched for vacuum leaks and cannot find anything. For troubleshooting I have a Actron 9575 OBDII scanner and it shows the PID outputs in real time and a freeze frame of when the code was set, but I honestly do not know what I'm looking at.
The PO became ill and car sat for 12-18 months with very little to no operation, could the injectors be dirty?
Any help is much appreciated.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
When does the code occur, idling? What are the short and long fuel trims when the code occurs? What are they typically when it's running? What does the O2 sensor do in the conditions where the code might be set?
I believe the code is saying it's so lean the computer can't trim the fuel enough to get back to the correct AFR. An injector not working one one cylinder might cause such an issue. Try checking the temps on each header primary tube to see if one is way cooler.
The code indicates bank 1, which is the drivers side of the engine.
I believe the code is saying it's so lean the computer can't trim the fuel enough to get back to the correct AFR. An injector not working one one cylinder might cause such an issue. Try checking the temps on each header primary tube to see if one is way cooler.
The code indicates bank 1, which is the drivers side of the engine.
Melting Slicks
Joined: Feb 2001
Posts: 2,804
Likes: 358
From: Northville, MI
It means your drivers side engine bank is running too lean. Of the many causes are:
A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor
A code P0171 may mean that one or more of the following has happened: The MAF (Mass Air Flow) Sensor is dirty or faulty Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry. There could be a vacuum leak downstream of the MAF sensor Possible cracked vacuum or PCV line/connection Faulty or stuck open PCV valve Failed or faulty oxygen sensor (bank 1, sensor 1) Sticking/plugged or failed fuel injector Low fuel pressure (possible plugged/dirty fuel filter!) Exhaust leak between engine and first oxygen sensor
Thread Starter
Instructor
Joined: Dec 2012
Posts: 191
Likes: 23
From: Louisville KY
I normally notice this DTC immediately after restart on a short stop, but it has happened while driving once or twice. I did check the header temps, but it is hard to geat a consistent reading. I think they are all within 10-20° of one another.
Freeze frame data from code:
ABSLT TPS% 5.1
Eng speed 800
calc load 2.0
Maf lb/m .96
Map HG 10.0
coolant 194
st ftrm1% -.08
lt ftrm1% 25.0
st ftrm2% -.08
lt ftrm2% 25.0
speed mph 0
fuel sys1 clsd
fuel sys2 clsd
PID's while running
abslt tps% 5.5
engine rpm 789-817
calc load 2.0
maf lb/m .92-.93
map hg 10.0
coolant 185
IAT 45
IGNADV 15-18
Second air Atmos
st ftrm1% -1.6 - +1.6
lt ftrm1% 25.0
st ftrm2% -2.3 - 0
lt ftrm2% 25.0
veh speed 0
fuel sys1 clsd
fuel sys2 clsd
02S11(V) 0.145 - 0.810
st ftrm11% -.08 - +0.8
02S12(V) 0.125 - 0.675
02S21(V) 0.095 - 0.820
st ftrm21 -.80 - +1.6
02S22(V) 0.085 - 1.0
Hopefully this tells provides some direction. FYI, I have already cleaned the MAF with MAF spray, no change.
Freeze frame data from code:
ABSLT TPS% 5.1
Eng speed 800
calc load 2.0
Maf lb/m .96
Map HG 10.0
coolant 194
st ftrm1% -.08
lt ftrm1% 25.0
st ftrm2% -.08
lt ftrm2% 25.0
speed mph 0
fuel sys1 clsd
fuel sys2 clsd
PID's while running
abslt tps% 5.5
engine rpm 789-817
calc load 2.0
maf lb/m .92-.93
map hg 10.0
coolant 185
IAT 45
IGNADV 15-18
Second air Atmos
st ftrm1% -1.6 - +1.6
lt ftrm1% 25.0
st ftrm2% -2.3 - 0
lt ftrm2% 25.0
veh speed 0
fuel sys1 clsd
fuel sys2 clsd
02S11(V) 0.145 - 0.810
st ftrm11% -.08 - +0.8
02S12(V) 0.125 - 0.675
02S21(V) 0.095 - 0.820
st ftrm21 -.80 - +1.6
02S22(V) 0.085 - 1.0
Hopefully this tells provides some direction. FYI, I have already cleaned the MAF with MAF spray, no change.
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
Your LTFT for both banks being at 25 means the PCM is basically putting all the extra fuel it can trying to get the AFR down to 14.7:1. Both banks are similar so it's not an issue with one side only.
It sounds like you have already done some investigation and the general condition of the engine is OK. Your primary tube measurements seem to be OK, indicating all cylinders are getting fuel and firing. So, it's time to deep deeper.
First check is for vacuum leaks or any unmetered air leak after the MAF sensor as well as exhaust leak between the engine and O2 sensors (basically at the head or cracked manifold)
Second would be to check the fuel pressure.
Third would be to investigate the tuning.
It sounds like you have already done some investigation and the general condition of the engine is OK. Your primary tube measurements seem to be OK, indicating all cylinders are getting fuel and firing. So, it's time to deep deeper.
First check is for vacuum leaks or any unmetered air leak after the MAF sensor as well as exhaust leak between the engine and O2 sensors (basically at the head or cracked manifold)
Second would be to check the fuel pressure.
Third would be to investigate the tuning.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Your LTFT for both banks being at 25 means the PCM is basically putting all the extra fuel it can trying to get the AFR down to 14.7:1. Both banks are similar so it's not an issue with one side only.
It sounds like you have already done some investigation and the general condition of the engine is OK. Your primary tube measurements seem to be OK, indicating all cylinders are getting fuel and firing. So, it's time to deep deeper.
First check is for vacuum leaks or any unmetered air leak after the MAF sensor as well as exhaust leak between the engine and O2 sensors (basically at the head or cracked manifold)
Second would be to check the fuel pressure.
Third would be to investigate the tuning.
It sounds like you have already done some investigation and the general condition of the engine is OK. Your primary tube measurements seem to be OK, indicating all cylinders are getting fuel and firing. So, it's time to deep deeper.
First check is for vacuum leaks or any unmetered air leak after the MAF sensor as well as exhaust leak between the engine and O2 sensors (basically at the head or cracked manifold)
Second would be to check the fuel pressure.
Third would be to investigate the tuning.
Check every vacuum fitting (PCV/Brake Booster/small vacuum lines) and the air ducts between the MAF and TB for leaks.
Spray some brake parts cleaner on areas where vacuum can leak and if the idle or idle quality changes, you have a vacuum leak.
BC
Last edited by Bill Curlee; Mar 22, 2013 at 03:04 PM.
Team Owner
Joined: May 2003
Posts: 23,480
Likes: 9
From: East Meadow NY
St. Jude Donor '12
Wasn't there an issue with Z06's and aftermarket air intakes causing intermittent lean codes. The forum vendors were selling honey comb screens to help clean up the air flow to prevent these types of issues.
I saw this issue on my convertible after runs down the drag strip after I added an aftermarket air intake. I ended up getting a tune after I checked and rechecked everything for leaks and it has been fine since. My vert has a screen so it wouldn't help me.
Here is the thread from Halltech. They suggest making sure you are free of leaks and cleaning the MAF. Injector o-rings can be another hard to find source of un metered air.
http://forums.corvetteforum.com/c5-z...m-forever.html
I saw this issue on my convertible after runs down the drag strip after I added an aftermarket air intake. I ended up getting a tune after I checked and rechecked everything for leaks and it has been fine since. My vert has a screen so it wouldn't help me.
Here is the thread from Halltech. They suggest making sure you are free of leaks and cleaning the MAF. Injector o-rings can be another hard to find source of un metered air.
http://forums.corvetteforum.com/c5-z...m-forever.html
Last edited by chaase; Mar 22, 2013 at 04:59 PM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Thread Starter
Instructor
Joined: Dec 2012
Posts: 191
Likes: 23
From: Louisville KY
Lionel/Bill, the PO has used a Crane Cams Power max to adjust some parameters, so the car has a "custom" tune. I'm not sure what was changed, but I have the Power max, should simply return it to the stock program? Is it possible these adjustments have caused the problem?
I've searched for a vacuum leak and cannot find one. I'm wondering if some of the injectors are plugged on bank 1 since the car sat so long. My thoughts are to switch the injectors from bank to bank to see if the Code switches from bank 1 to bank 2. If it does not, I was planning on clearing the memory and have it relearn the idle?
Your thoughts please?
I've searched for a vacuum leak and cannot find one. I'm wondering if some of the injectors are plugged on bank 1 since the car sat so long. My thoughts are to switch the injectors from bank to bank to see if the Code switches from bank 1 to bank 2. If it does not, I was planning on clearing the memory and have it relearn the idle?
Your thoughts please?
Race Director
Joined: Apr 2007
Posts: 11,152
Likes: 890
From: South Western Ontario
You could try the stock tuning. That would at least put you back to a setup that should have worked well before modifying and should still work not too bad even with the mods.
I doubt it's really an issue with bank1. Bank2 is showing it's about the same amount of lean too. I would suspect bank1 is just slightly more lean and sets the code. Anything to make it a little more lean would likely set a bank2 code as well.
I doubt it's really an issue with bank1. Bank2 is showing it's about the same amount of lean too. I would suspect bank1 is just slightly more lean and sets the code. Anything to make it a little more lean would likely set a bank2 code as well.
Thread Starter
Instructor
Joined: Dec 2012
Posts: 191
Likes: 23
From: Louisville KY
OK, fuel pressure checks out at 58psi, no vacuum leaks to be found anywhere. MAF sensor cleaned again, injectors swapped from bank to bank, tuning returned to stock. Long term fuel trims are still at 25 for both banks but after 50 mile drive no codes. If the LTFT's are supposed to be near zero or at lest in the single digits, could the MAF be malfunctioning? Is there any way to test the MAF with very basic diagnostic tools?
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
YES!! It could be a MAF issue. If you can find another C5 you could swap MAFs
Look at the real time MAF air flow values. and compare them to another C5. They should be low at idle and increas as RPM rises.
When I get home tonight I will plug in my ACTRON CP9180 and see what mine are at idle and part throttle.
Do yours increase as RPM increases?
Bill
Look at the real time MAF air flow values. and compare them to another C5. They should be low at idle and increas as RPM rises.
When I get home tonight I will plug in my ACTRON CP9180 and see what mine are at idle and part throttle.
Do yours increase as RPM increases?
Bill
Thread Starter
Instructor
Joined: Dec 2012
Posts: 191
Likes: 23
From: Louisville KY
Bill, while checking the MAF reading I noticed my LTFTs are dropping, on start they were both at 12.5 and fell back to 9.4 in a matter of minutes. STFT's were still going negative. I'm beginning to think the filter is over oiled and contaminating the MAF readings..... At 800RPM the MAF is reading .86 which is slightly lower than my first recorded numbers. At 1500 RPM = 1.36, 2000 RPM = 1.9, 2500 RPM = 2.3. The RPMs are estimates; it’s hard to hold it steady.
Tech Contributor
Joined: Dec 1999
Posts: 32,910
Likes: 2,402
From: Anthony TX
CI 6,7,8,9,11 Vet
St. Jude Donor '08
Obtain some MAF Cleaner (I just use non colorinated brake parts cleaner) and spray out the MAF. Let the cleaner evaporate, hook it bak up and see how she runs.
BC
BC