Lean Misfire &Totally Perplexed

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January 28th, 2012, 11:40 AM

miscou1

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Lean Misfire &Totally Perplexed

<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <w:TrackMoves/> <w:TrackFormatting/> <w:PunctuationKerning/> <w:ValidateAgainstSchemas/> <w:SaveIfXMLInvalid>false</w:SaveIfXMLInvalid> <w:IgnoreMixedContent>false</w:IgnoreMixedContent> <w:AlwaysShowPlaceholderText>false</w:AlwaysShowPlaceholderText> <w

oNotPromoteQF/> <w:LidThemeOther>EN-US</w:LidThemeOther> <w:LidThemeAsian>X-NONE</w:LidThemeAsian> <w:LidThemeComplexScript>X-NONE</w:LidThemeComplexScript> <w:Compatibility> <w:BreakWrappedTables/> <w:SnapToGridInCell/> <w:WrapTextWithPunct/> <w:UseAsianBreakRules/> <w

ontGrowAutofit/> <w:SplitPgBreakAndParaMark/> <w:EnableOpenTypeKerning/> <w

ontFlipMirrorIndents/> <w:OverrideTableStyleHps/> </w:Compatibility> <m:mathPr> <m:mathFont m:val="Cambria Math"/> <m:brkBin m:val="before"/> <m:brkBinSub m:val="--"/> <m:smallFrac m:val="off"/> <m:dispDef/> <m:lMargin m:val="0"/> <m:rMargin m:val="0"/> <m:defJc m:val="centerGroup"/> <m:wrapIndent m:val="1440"/> <m:intLim m:val="subSup"/> <m:naryLim m:val="undOvr"/> </m:mathPr></w:WordDocument> </xml><![endif]--> I’m trying to troubleshoot a Lean Misfire on my 2005 Suburban 5.3L “T” engine. I have replaced all of the spark plugs and wires as a start. The PCM is throwing the following codes, in this order, P0300 (misfire), P0131 (low Voltage Bank1, Sense 1), and P0171 Too Lean Bank 1). Also when I changed the plugs I noticed that all four plugs on the driver’s side of the motor showed a dry black carbon on them. The four plugs on the passenger side of the motor looked totally normal. Which confirmed that the problem seems to be specific to one side of the motor (Drivers side) based on the condition of the plugs and the DTC’s only coming from one bank of the motor (Bank 1). So I’m reasonably sure I have a “Lean Misfire” condition.
All of this is resulting in a rough idle at slow RPM. The truck starts fine and idles normal when cold (I assume this is because of the extra fuel provide by the PCM for the cold engine) once at full temperature the idle gets rough and I start throwing the lean codes on Bank 1. Sometimes, after about 20 minutes of driving the car, it runs and idles perfectly (I assume this is the PCM adjusting the short term fuel average). Upon a hot restart, the rough idle returns immediately.
Because I know the plugs and wires are good, I pulled both fuel rails and moved all four of the injectors from the driver’s side to the passenger side; and the passenger side injectors were moved to the driver’s side. My thought was that if the lean codes started to appear on the Bank 2 side, I could narrow the problem down to a fuel injector. However after swapping all of the fuel injectors to the opposite side of the motor, the problem persists on the bank 1 side (Driver’s side). The only thing that seemed odd was that the Bank 1 Fuel Rail (On the number 1 piston side of the motor) had something rattling around in it. It seemed to be a large object and I noticed that the bank 2 fuel rail did not have the rattle when empty of fuel. Since Bank one is the fuel delivery side, I was wondering if the Bank 1 fuel rail had some type of baffle in it that is supposed to move, or if the baffle broke loose. I suppose I could order a new one and see of the new part has the same rattle. This should answer the question. Has anyone ever worked on or replaced 5.3L V-8 fuels rails and noticed this? Perhaps this loose object is restricting fuel flow, but if this were the case, the problem should get worse with more load on the engine. My rough idle gets better at higher RPM (again, indicative of a “Lean Misfire condition).
The next thing I did was to remove the entire air intake system and check it for any leaks. I cleaned the MAF and checked to make sure the filter was clean (it is very new) and that all of the clamps were secure. I also cleaned the whole area around the throttle body to make sure it was not stuck slightly open by crud. This did not resolve the problem. I am inclined to rule out a bad MAF because only one side of the motor (Bank 1) is demonstrating the lean condition. I would think that a bad MAF would affect both sides.
A few threads and web sites point to a stuck EGR valve as the source of the additional air, but he 2005 5.3L V-8’s were the first year of the “drive by wire” gas pedal and the non-return fuels system. I have been all over the exhaust manifolds and do not see any indication of an exhaust gas return circuit. It looks as though EGR system that was present it the 200-2004 models has been replaced. I have also checked to make sure all of the intake manifold bolts are tight, and that the throttle body housing bolts are secure. At this point’ I’m totally baffled? Any thought would be appreciated……

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January 28th, 2012, 11:55 AM

EinST

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Welcome to the forum.

I'd troubleshoot P0131 first. The bank 1 pre-catalyst O2 sensor is reporting stationary, low voltage. The PCM interprets the low voltage as oxygen-rich, i.e., lean condition. It then commands more fuel until it sets P0171. The P0300 means uneven contribution to crankshaft output from multiple cylinders.

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January 28th, 2012, 2:15 PM

miscou1

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Thanks, EinST. Intereresting observation. I didn' realize the PCM was "Smart" enough to adjust the fuel/air mixture on just one side of the motor. Any problem with the Pre cat O2 sensore would instruct the PCM to alter the amount of fuel, hence explainign why the plugs on one side of the motor looked very different than the other. I'm going to do a little more investigation and be sure to check the entire run of the O2 sensor, sonnections, a wires to ensure they did not melt against the exhuast pipe somewhere. Thank you for the feedback.

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January 29th, 2012, 9:03 AM

miscou1

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I've checked the run of the wire from sensor to connection, and checked connectivity and resistance at the sensor wire connector. I found some mild abrasion on one of the two heather wires, the ground and sensor wires looked good. All of it seems to be working properly. I'm going to get a new Pre-Cat O2 sensor today and see if that fixes the problem.

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January 29th, 2012, 7:50 PM

MDTAHOE

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Do you have a scan tool that shows data?

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January 29th, 2012, 7:57 PM

MDTAHOE

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Bulletin No.: 05-06-04-063

Date: October 12, 2005

TECHNICAL

Subject:
LM7, L59 or L33 Engines with Cold Start Rough or Incorrect Idle, Misfire, Malfunction Indicator Lamp (MIL) or Flashing Requiring 02 Sensor Replacement (Reprogram PCM)
Models:
2004-2005 Cadillac Escalade
2004-2005 Chevrolet Avalanche, Silverado 1500, Suburban, Tahoe
2005 Chevrolet Silverado Hybrid (HP2)
2004-2005 GMC Sierra 1500, Yukon, Yukon XL
2005 GMC Sierra Hybrid (PH2)
with Vortec 5300 5.3L V-8 Engine (VINs T, Z, B - RPOs LM7, L59, L33)

Condition

Some customers may comment on a Malfunction Indicator Lamp (MIL) On or that the MIL is flashing. An actual engine misfire may or may not be felt along with an incorrect idle speed. Typically this occurs during cold winter months, on cold engine starts. Some vehicles may have been previously serviced for the same condition. Technicians may also find the following DTCs stored with the Tech 2(R) P0131, P0133, P0134, P0137, P0138, P0140, P0151, P0153, P0154, P0157, P1133, which may be in conjunction with P0171, P0174, P0300 and P1138.

Cause

Water shock occurs when water droplets are present in the exhaust. The water in the exhaust contacts the sensor element inside the H02 sensor, causing the H02 sensor element to crack.

Correction

Upon diagnostic investigation, the technician may find that the H02 sensor requires replacement. In addition to replacing the affected H02 sensor, these vehicles should also be reflashed with the latest PCM calibration. An updated PCM calibration will be available to dealerships as part of TIS 2000 incremental satellite update 11.0 (NAO version 25.010) or greater. Always, make sure your Tech 2 is updated with the latest software version.

Important: If a DTC P0420 or P0430 is stored along with DTC(s) P0300, the catalytic converter diagnostics in Service Information (SI) must be followed to determine if the catalytic converters are operating properly.
Warranty Information

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February 1st, 2012, 8:28 PM

miscou1

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Very interesting. I was visiting my Wife's family in Canada over the Christmas holiday when I for the first DTC and rough idle. I was very cold (Much colder than Virginia) the morning the problem started, and the MIL came on. I replaced the Bank 1 Pre-Cat sensor and the problem was immediately fixed. I'm back to 21.5 mpg@60 mph. Thanks for the help!

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