P0300

[Hounds]

Hi guys. TOtally new to this forum. I just got a 2005 sierra 2500. 6.0L Gas.
I've owned Dodge and Ford pu's for years but my neighbor sold me her old one with 150,000 in VERY good condition so I took it.

I know this is beaten to death but I have the code. I am not a mechanic but fairly good and have minimal tools .

So far all I did was change the plugs and wires and spray the air intake manifold real good all the way around with carb cleaner and the engine never hesitated or anything.
Does that necessarily mean its NOT the gasket?

What should my next step be? Should I just change all the coils?

I've also ran seafoam through the system for 3 tank fills. Not sure that does Jack, but some other guy said to do that.

It seems to be after a real good drive for an hour at 65 that the light comes on.

THanks.

 

[Hounds]

So, I decided to unplug each coil as engine was running. Nothing changed. But question should I have let it warm up real good? Because that's when the code pops up. Or does a bad coil would it have made the engine change immediately?

I will check fuel pressure next. Can a DIY pressure gauge/tester be made? or no?

 

[winger870]

Just putting the 3 info pages out there for you,
to possibly assist you with your issue.



Important Information - PIP 3893A
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#PIP3893A: Intermittent Engine Misfire And SES Light Due To Loss Of Voltage To Ignition Coils - keywords connector miss P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 P0351 P0352 P0353 P0354 P0355 P0356 - (Dec 3, 2008)

Subject: Intermittent Engine Misfire and SES Light due to Loss of Voltage to Ignition Coils

Models: 2005-2006 Cadillac Escalade
2005-2006 Chevrolet Avalanche, Express, Silverado, Suburban, Tahoe
2005-2006 GMC Savana, Sierra, Yukon
Equipped with a 4.8L, 5.3L, or 6.0L V8 Engine
(RPO Codes LR4, LM7, LQ4, or LQ9)

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Condition/Concern:
On rare occasions, a customer may complain of a misfire and SES light. Upon inspection, no spark from the ignition coils may be observed and any of the following DTCs may be stored: P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0351, P0352, P0353, P0354, P0355, P0356, P0357, and/or P0358.

Recommendation/Instructions:
If the diagnosis does not isolate a cause for this concern, wiggle test the ignition coil harnesses to see if the concern can be duplicated. If so, the following areas could be causing an intermittent loss of ignition 1 voltage to the ignition coils and should be inspected:

For C/K Trucks and Utilities, inspect S160, S159, C148, and C149 for poor connections. Also, inspect the circuits on both sides of C148 and C149 to see if any are broken inside of the insulation, especially the pink ignition 1 power feed circuit.
For G Vans, inspect S184, S185, C126, and C127 for poor connections. Also, inspect the circuits on both sides of C126 and C127 to see if any are broken inside of the insulation, especially the pink ignition 1 power feed circuit.
If a concern is found with any of these areas, it should be repaired by following the repair procedures.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.

 

[winger870]

Powertrain Controls Diagnosis
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DTC P0300

SYSTEM DESCRIPTION
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the camshaft position (CMP) sensor in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0300 Engine Misfire Detected

CONDITIONS FOR RUNNING THE DTC
DTCs P0101, P0102, P0103, P0106, P0107, P0108, P0116, P0117, P0118, P0125, P0128, P0220, P0315, P0335, P0336, P0341, P0342, P0343, P0502, P0503, P1114, P1115, P1120, P1258 are not set.
The engine speed is between 450-5,000 RPM .
The ignition voltage is between 10-18 volts .
The engine coolant temperature (ECT) is between -7 and +130°C (+19 and +266°F) .
The fuel level is more than 10 percent .
The throttle angle is steady within 1 percent .
The antilock brake system (ABS) and the traction control system (TCS) are not active.
The transmission is not changing gears.
The A/C clutch is not changing states.
The PCM is not in fuel shut-off or decel fuel cut-off mode.
The PCM is not receiving a rough road signal.
DTC P0300 runs continuously once the above conditions are met.
CONDITIONS FOR SETTING THE DTC
The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.

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
Excessive vibration from sources other than the engine could cause DTC P0300 to set. The following are possible sources of vibration:
Thickness variation of the brake rotors - Refer to Symptoms - Hydraulic Brakes in Hydraulic Brakes. See: Brakes and Traction Control\Hydraulic System\Testing and Inspection\Symptom Related Diagnostic Procedures\- Symptoms - Hydraulic Brakes
The drive shaft not balanced - Refer to Vibration Analysis - Driveline in Vibration Diagnosis and Correction. See: Testing and Inspection\Symptom Related Diagnostic Procedures\Vibration Diagnosis and Correction\Diagnostic Information and Procedures\Vibration Analysis - Driveline
Worn or damaged accessory drive belt - Refer to Symptoms - Engine - 4.8L, 5.3L and 6.0L. See: Engine, Cooling and Exhaust\Engine\Drive Belt\Testing and Inspection
There may be more or less cylinders actually misfiring than indicated by the scan tool.
Spray water on the secondary ignition components using a spray bottle. Look and listen for arcing or misfiring.
If there are multiple misfires on only one bank, inspect the fuel injector and ignition coil, power and ground circuits for that bank. Refer to Computers and Control Systems Schematics.
TEST DESCRIPTION


Steps 1-7
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Steps 8-20
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Steps 21-23
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The number below refers to the step number on the diagnostic table.

If the actual CKP variation values are not within the learned values, the misfire counters may increment.


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[winger870]

Important Information - PIP 3056
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Subject: 97-05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires on One Bank - kw CEL diagnostics driveability DTC P0171 P0172 P0174 P0175 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 #PIP3056 - (07/12/2004)

Models: (00-05 Cadillac Escalade - C6 and K6) and (02-05 Chevrolet Avalanche - C1, C2 K1 and K2) and (99-05 Chevrolet Silverado - C1, C2 K1 and K2) and (00-05 Chevrolet Suburban - C1, C2, K1 and K2) and (00-05 Chevrolet Tahoe - C1 and K1) and (99-05 GMC Sierra C1, C2 K1 and K2) and (00-05 GMC Yukon - C1, C2, K1 and K2) and (03-05 Chevrolet Express G1, G2, G3, H1, H2 ) and (03-05 GMC Savana G1, G2, G3, H1, H2 ) and (04-05 Buick Rainier S1, T1 ) and (03-05 Chevrolet Trail Blazer EXT S1, T1 ) and (03-05 GMC Envoy XL XUV S1, T1 ) and (03-05 Hummer H2) and (04-05 Cadillac CTS-V DB) and (98-02 Chevrolet Camaro FB) and (97-04 Chevrolet Corvette YB) and (98-02 Pontiac Firebird FB) and (04-05 Pontiac GTO VB)

The following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Condition/Concern:
Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

Recommendation/Instructions:
If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:
Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.
Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.
Check for excessive exhaust backpressure using the restricted exhaust diagnosis.
Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.
Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.

NOTE: GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition.