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PostPosted: Sun Feb 28, 2016 8:41 pm 
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Year and Trim: 2005 Gxp
I recently took my car into the dealer to get some work done to it, few things with the front need as well as trying to get the codes Po171 & Po174 to go away. They checked all over and there are zero vacuum leaks so they told me it could be the K&N drop in filter I put in but I told them the codes were there before the filter. So they changed the fuel filter and did and full fuel system clean including tb cleaning, injector and fuel rail cleaning with a machine. I got my car back the next day and the cel was off. Sure enough the day after that it came back on and I got the codes Po171 bank 1 too lean, po507 Iac system Rpm higher than expected, and po300 for a misfire. I've never gotten the misfire or iac codes before I took it in for work. I cleared the codes and the cel came back on the next day reading only Po171 & Po174 banks 1 & 2 lean. 174 was not there the day before and the other codes had not come back. Another thing to note was when I was decelerating to a stop from about 65mph the rpm was fluctuating/jumping up and down a little bit as I neared the stop so I'm thinking the iac needs replaced but still have the lean codes mystery? And the miss fire as well? I was going to have plugs changed in a few weeks as well. What could the missfire be? Any help would be appreciated greatly. Thanks!


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PostPosted: Sun Feb 28, 2016 9:31 pm 
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Have you checked the bolts on the intake manifold? These are notorious for loosening off with time. I've had to torque mine a few times on both my GXP and my STS (both are Northstar engines but very different). Many dealer technicians I've spoken to have had no knowledge of this problem despite it being commonly reported in many different forums. When I first discovered mine, several weren't even finger tight.

Here is the torque sequence and spec. Do not over-torque these. Since this is a transverse mounted engine, "FRONT" in this case refers to the passenger side of the car.

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Last edited by ddalder on Mon Feb 29, 2016 3:46 am, edited 1 time in total.

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PostPosted: Sun Feb 28, 2016 9:56 pm 
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Ok, I know this may sound a bit abrasive, but this code, along with P0420, and several others are some of the most common codes on GM vehicles and I answer them routinely here, which means if you use the search feature, you'd find all you need to know. Utilizing the search feature of this forum, typing in "P0171" will find you the information, like the link I am posting below.

9 times out of 10, it is a HO2S related.

bonneville-gxp-northstar-powered-cars/topic30881.html?hilit=p0171

However, P0507 WILL NOT SET if P0171/P0174 are present and P0171/P0174 WILL NOT SET if P0507 is set. So these are each independent events happening at separate times.

P0507 is the IAC trying to correct for something and not being able to causeing the engine to run 100 rpm higher than desired, and the PCM detects that the IAC test has failed 3x per ignition cycle.

Some things to look for;

• High resistance in an IAC valve control circuit

• The correct positive crankcase ventilation (PCV) valve, properly installed and proper operation of the PCV valve

• Proper operation and installation of all air intake components

• Proper installation and operation of the mass air flow (MAF) sensor

• A tampered with or damaged throttle stop screw

• A tampered with or damaged throttle plate, throttle shaft, throttle linkage, or cruise control linkage, if equipped

• A skewed high throttle position (TP) sensor

• Excessive deposits in the IAC passage or on the IAC pintle

• Excessive deposits in the throttle bore or on the throttle plate

• Vacuum leaks

• A high or unstable idle condition could be caused by a non-IAC system problem that cannot be overcome by the IAC valve.

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Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

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PostPosted: Sun Feb 28, 2016 11:32 pm 
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Year and Trim: 2005 Gxp
Here is my freeze frame information:
for Po174
Calc load: 43.1%
Coolant temp: 196
ST FTRM: 7.8
LT FTRM: 20.3
ST FTRM2: 1.6
LT FTRM2: 23.4
MAP: 18.3
Eng Rpm: 2590
Veh Speed: 78
IGN ADV: 46.5
IAT: 61
MAF: 4.62
ABSLT TPS: 15.3
***Also the scanner says both O2s check ok


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PostPosted: Sun Feb 28, 2016 11:40 pm 
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Thank you both for the info. And ddalder, I haven't heard that one before, that sounds like it's worth a try. Would it be realistic for those codes to show up if the intake manifold gaskets failed? Would it be probable for both gaskets to fail at once?


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PostPosted: Mon Feb 29, 2016 12:22 am 
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When you say your scanner says both your post-cat HO2S's are fine, it simply means that they are recognized and operating. That doesn't mean they're operating correctly.

Your LTFT's tell you exactly why this code triggered;

Quote:
The average long term fuel trim value is above 19 percent.

The above condition is present for 90 seconds.


From GM;
Quote:
DTC P0171 or P0174
Circuit Description
The powertrain control module (PCM) controls the air/fuel metering system in order to provide the best possible combination of driveability, fuel economy and emission control. Fuel delivery is controlled differently during Open and Closed Loop. During Open Loop the PCM determines fuel delivery based on sensor signals without oxygen sensor input. During Closed Loop the PCM adds oxygen sensor inputs and level of purge to calculate Short and Long Term fuel trim adjustments. If the oxygen sensors indicate a lean condition, fuel trim values will be above 0 percent . If the oxygen sensors indicate a rich condition, fuel trim values will be below 0 percent. The values for the Short Term fuel trim change rapidly in response to the heated oxygen sensor (HO2S) voltage signals. Long Term fuel trim makes coarse adjustments in order to maintain an Air/Fuel Ratio of 14.7:1. A block of cells contain information arranged in combinations of engine RPM and engine load for a full range of vehicle operating conditions. The long term fuel trim diagnostic is based on an average of cells currently being used. The PCM selects the cells based on the engine speed and engine load. If the PCM detects an excessively lean condition, DTC P0171 or P0174 sets.

DTC Descriptors
This diagnostic procedure supports the following DTCs:

• DTC P0171 Fuel Trim System Lean Bank 1

• DTC P0174 Fuel Trim System Lean Bank 2

Conditions for Running the DTC
• DTCs P0030, P0036, P0050, P0056, P0101, P0102, P0103, P0107, P0108, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0142, P0150-P0158, P0160, P0161, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0300, P0401, P0403, P0404, P0405, P0410, P0442, P0443, P0446, P0449, P0452, P0453, P0455, P0496, P0506, P0507, P1133, P1134, P1153, P1154, P1404, are not set.

• The engine coolant temperature (ECT) is between -40 to +127°C (-40 to +261°F).

• The intake air temperature (IAT) is more than -7°C (+19.4°F).

• The manifold absolute pressure (MAP) is more than 5 kPa (0.73 psi).

• The vehicle speed is less than 134 km/h (83 mph).

• The engine speed is between 400-6,000 RPM.

• The barometric pressure (BARO) is more than 74 kPa (10.7 psi).

• The mass air flow (MAF) is more than 0.5 g/s.

• The fuel level is more than 10 percent.

• DTC P0171 and P0174 run continuously once the above conditions have been met.

• The engine is in Closed Loop fueling.

Conditions for Setting the DTC
The average long term fuel trim value is above 19 percent.

The above condition is present for 90 seconds.

Action Taken When the DTC Sets
• The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• A current DTC, Last Test Failed, clears when the diagnostic runs and passes.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Clear the MIL and the DTC with a scan tool.

Diagnostic Aids
• The system will go lean if an injector is not suppling enough fuel.

• The system will go lean during high fuel demand.

• Using a scan tool, review the Failure Records. If an intermittent condition is suspected, refer to Intermittent Conditions .

• Excessive resistance in the fuel injector ignition 1 voltage circuit or the fuel injector control circuit may cause the following symptoms:

- Lean condition

- Misfire

- Rough idle

Test Description
The numbers below refer to the step numbers on the diagnostic table.

If no problems are found, a worn cam, worn intake or exhaust values or other engine mechanical failures may be at fault.

Step 1
Did you perform the Diagnostic System Check - Vehicle?
--
Yes: Go to Step 2
No: Go to Diagnostic System Check - Vehicle in Vehicle DTC Information

Step 2
Important: If any DTCs are set, other than P0171, refer to those DTCs before continuing.

- Install a scan tool.
- Start and idle the engine at normal operating temperature in Closed Loop.
- Record the Long Term Fuel Trim data.
- Turn OFF the engine.
- Turn ON the ignition, with the engine OFF.

Review the Freeze Frame/Failure Records and record displayed data for this DTC.

Does the scan tool indicate that the long term fuel trim is greater than the specified value?
19%
Yes: Go to Step 3
No: Go to Diagnostic Aids

Step 3
- Operate engine at idle.
- Observe the HO2S parameters with a scan tool.

Are the HO2S parameters within the specified range and fluctuating?
200-800 mV

Yes: Go to Step 4
No: Go to Step 5

Step 4
- Turn OFF the engine.
- Inspect the following conditions:
• Vacuum hoses for splits, restrictions, and improper connections--Refer to Emission Hose Routing Diagram .

• Ensure that the vehicle has sufficient fuel in tank. If fuel pressure is too low this DTC may set. Refer to Fuel System Diagnosis .

• Fuel contamination--Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

Did you find and correct the condition?
--
Yes: Go to Step 7
No: Go to Step 6

Step 5
- Turn OFF the engine.
- Inspect for the following conditions:
• The heated oxygen sensor (HO2S) for proper installation

• The electrical connectors and the wires are secured and not contacting the exhaust system

Inspect for a short between the signal circuit and the low reference circuit.
Did you find and correct the condition?
--
Yes: Go to Step 4
No: Go to Fuel System Diagnosis

Step 6
Operate the engine at idle and inspect for the following conditions:

• Any missing, loose, or leaking exhaust components

• Any vacuum leaks at the intake manifold and injector O-rings

• The air induction system and air intake ducts for vacuum leaks and restrictions

• The crankcase ventilation system for leaks--Refer to Crankcase Ventilation System Inspection/Diagnosis in Engine Mechanical.

Did you find and correct the condition?
--
Yes: Go to Step 7
No: Go to Symptoms - Engine Mechanical in Engine Mechanical

Step 7
Important: After repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel.

-Turn ON the ignition, with the engine OFF.
-Clear the DTCs with a scan tool.
-Turn OFF the ignition for 30 seconds.
-Start the engine.

Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

Did the DTC fail this ignition?
--
Yes: Go to Step 2
No: Go to Step 8

Step 8
Observe the Capture Info with a scan tool.

Are there any DTCs that have not been diagnosed?
--
Yes: Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information
No: System OK

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2015 Chrysler Town & Country Limited Platinum: Mommy's NEW RGC
2007 Chrysler Town & Country Limited: Daddy's beater affectionately called the Rolling Garbage Can or "RGC" for short
2009 Chevrolet Impala SS: LS4 V8, Victory Red
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Mon Feb 29, 2016 12:54 am 
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bonniegxp_97 wrote:
Thank you both for the info. And ddalder, I haven't heard that one before, that sounds like it's worth a try. Would it be realistic for those codes to show up if the intake manifold gaskets failed? Would it be probable for both gaskets to fail at once?

The intake on the LD8 engine actually uses 8 individual seals, one for each cylinder. There is no coolant that flows through the intake, it's simply a case of it loosening off permitting the entry of unmetered air. Wherever it loosens and separates permits an opportunity for problems.

I've definitely experienced a rough idle and hesitation on acceleration until the engine warmed up when bolts were loose.

Lane has pointed out numerous possible faults that need to be checked. The reason I mentioned this specifically is because it can contribute to the problem and is a well-known, frequently documented finding among forum members (GXP, Cadillac DeVille/DTS, Cadillac STS, etc) who have checked the bolts. Whether it solves the problem or not, you should check this and tighten if necessary. At least then you've eliminated a potential contributing factor.

Because pictures always seem to help visualize text, here's a photo of the underside of the LD8 intake...

Image

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PostPosted: Mon Feb 29, 2016 1:07 am 
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To Darcy's point, at 89 in/lbs torque spec, just like the cam cover bolts, heat cycling just works them loose over time. So it is a very strong possibility that those bolts could be loose, allowing unmetered air in.

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Retired Bonneville Owner and former GM Tech:
2004 Pontiac Bonneville GXP: Black/Ebony *SOLD*

Summer Toys: Combined 827 RWHP / 877lb/ft RWTQ
2004 Pontiac GTO: Impulse Blue Metallic/Black/M6: lots 'o mods, 415 RWHP / 405lb/ft RWTQ!
2006 Cadillac STS-V: Light Platinum Metallic/Light Gray/A6 - Spectre CAI, Magnaflow exhaust, Speed Inc. tune, 412 RWHP / 472lb/ft RWTQ

Daily Drivers:
2015 Chrysler Town & Country Limited Platinum: Mommy's NEW RGC
2007 Chrysler Town & Country Limited: Daddy's beater affectionately called the Rolling Garbage Can or "RGC" for short
2009 Chevrolet Impala SS: LS4 V8, Victory Red
1999 Chevrolet Suburban: Sunset Gold Metallic - Daddy's winter beater and plow truck


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PostPosted: Mon Feb 29, 2016 3:05 am 
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Thank you both for your input. I will follow the steps CMN posted in the link as well as for for sure retourqe those bolts as ddalder pointed out and the picture was indeed helpful. When I go to check these bolts should I loosen then retorque to spec and in what pattern? Loosen all at once and start in a certain pattern? Or torque one at a time without loosening? Or loosen then torque one at a time? Thanks again for your replies guys it means alot! :hail: :hail:


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PostPosted: Mon Feb 29, 2016 3:35 am 
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The correct torque sequence is in the first picture I posted. Basically, start in the middle and work out in a circular pattern. Any of the times I've done mine I did not loosen them first. I'm not sure what the "official" answer to that is but I simply started at bolt #1 and continued from there.

I found it very helpful to use a 1/4" drive torque wrench with a short socket and about a 4" extension. This allowed me to access all the bolts without having to remove the fuel rail or other components. Most of the 3/8" and all the 1/2" drive torque wrenches I've ever seen don't adjust low enough for this spec.

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RainSense Wipers, Backup Camera, '00 Style Door Panel Courtesy Lights, Heated Washer Solvent, 2X Remote Trunk Release,
Turn Signal Mirrors, Center Console Courtesy Lamp, Rear Outboard Heated Seats, PVD Chrome 18" Factory Rims, Upgraded
Carbon Fibre Appearance Interior Trim, Highly Modified Main Body Harness, Instrument Panel, Door, Door Panel & Headliner
Wiring Harnesses, Custom Fuse Box & Tire and Loading Information Decals, Additional Acoustic Insulation


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PostPosted: Mon Feb 29, 2016 6:22 pm 
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Very helpful I'll try it out tonight and let you guys know if it works


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PostPosted: Mon Feb 29, 2016 9:24 pm 
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Well I tried to retorque the bolts but I just can't access them with the big torque wrench I have, the 1/2" drive one but goes down to 25 in/lbs. I couldn't get to the bolts well enough to torque them even with the 1/2-->1/4 adapter and a swivel. There's just not enough clearance due to the fuel rails let alone the big clumsy 1/2 drive wrench. How difficult is it to remove the rails? Also I sprayed a bunch of carb cleaner all around where the manifold meets the gaskets and there was no change in idle. So that would mean there's no vac leaks there right?


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