Is this the Intake Gasket Issue?

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Circuit Description
The Heated Oxygen Sensor (HO2S) is a sensor designed to create a voltage relative to the oxygen content in the engine exhaust stream. The Control Module (PCM/VCM) supplies the HO2S with signal High and Low circuits. Ignition voltage and ground is supplied to the HO2S heater by independent circuits. The oxygen content of the exhaust indicates when the engine is operating lean or rich. When the HO2S detects that the engine is operating rich, the signal voltage is high, and decreases the signal voltage as the engine runs leaner. This oscillation above and below the bias voltage, sometimes referred to as activity or switching, can be monitored with the HO2S signal voltage.

The HO2S contains a heater that is necessary in order to quickly warm the sensor to operating temperature and maintain the operating temperature during extended idle conditions. The HO2S needs to be at a high temperature in order to produce a voltage. Once the HO2S has reached operating temperature, the Control Module monitors the HO2S bias, or reference, voltage as well as the HO2S signal voltage for closed loop fuel control. During normal Closed Loop fuel control operation, the Control Module will add fuel (enriches the mixture) when the HO2S detects a lean exhaust content and subtract fuel (leans-out the mixture) when the HO2S detects a rich exhaust condition.

Certain vehicle models utilize an oxygen sensor after the catalyst converter in order to monitor catalyst efficiency.

This DTC determines if the HO2S is functioning properly by checking for an adequate number of HO2S voltage transitions above and below the bias range of 300-600 mV. This DTC sets when the VCM fails to detect a minimum number of voltage transitions above and below the bias range during the test period. Possible causes of this DTC are listed below.

• An open or a short to voltage on either the HO2S signal or HO2S low circuits.
• A malfunctioning HO2S.
• A problem in the HO2S heater or its circuit.
• A poor HO2S ground.

This DTC determines if the post-converter HO2S heater circuit is functioning properly by monitoring the amount of time required for the HO2S to reach operating temperature. This DTC sets when the VCM fails to detect HO2S voltage transitions above and below the bias range within a specified amount of time. Possible cause of this DTC are listed below.

• An open circuit in either the HO2S ignition positive voltage or the HO2S heater ground circuits.
• An HO2S heater element problem.

Conditions for Running the DTC

Important: This test is void if the system voltage remains outside the specified range for more than 4 seconds

• The system voltage is between 11.7-18 volts
• The MAF is less than 35 g/s
• The engine run time is more than 2 seconds
• The ECT is less than 33°C (91°F)
• The IAT is less than 33°C (91°F)
• The difference between the ECT and IAT is 5°C (9°F) or less

Conditions for Setting the DTC
The HO2S voltage remains within 150 mV of the start-up voltage for 245 seconds after cold start.

Action Taken When the DTC Sets

• The Control Module illuminates the Malfunction Indicator Lamp (MIL) if a failure is detected during 2 consecutive key cycles.
• The Control Module will set the DTC and records the operating conditions at the time the diagnostic fails. The Control Module stores the failure information in the scan tools Freeze Frame and/or the Failure Records.

Conditions for Clearing the MIL/DTC

• The Control Module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
• A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
• Use the scan tool Clear Information function.

Diagnostic Aids

Important: Never solder the HO2S wires.

Check for the following conditions:
An intermittent may be caused by any of the following conditions:

• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation.

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Symptom Related Diagnostic Procedures

Test Description
The number(s) below refer to the step number(s) on the Diagnostic Table.

2. As the heater warms the oxygen sensor to operating temperature, the HO2S will output a voltage in relation to the amount of oxygen in the exhaust. With the ignition ON and the engine OFF the exhaust usually contains a high oxygen content. With the engine OFF the HO2S voltage will usually decrease from the initial (bias) voltage due to the high oxygen content.

4. This step checks for proper HO2S heater ignition feed and ground supply.

5.This step checks for proper VCM and signal circuit operation.

 

[SunlitComet]

Circuit Description
The Crankshaft Position (CKP) Sensor is the primary input to determine if misfire is occurring. Engine misfire is detected by monitoring crankshaft speed variations between cylinders. If a crankshaft deceleration occurs during a combustion or power stroke, the Control Module (PCM/VCM) will compare this change in crankshaft speed to the previous cylinder. If the crankshaft speed change is more than a maximum allowable speed, the misfire is detected. Misfire may occur in a specific cylinder or all cylinders randomly.

When an engine is misfiring, brief decelerations in crankshaft rotational speed will be detected by the CKP. The Control Module determines which cylinder has misfired based upon the Camshaft Position CMP Sensor input. Misfire data is stored for each cylinder in separate accumulators. After 100 combustion events, the misfire totals are compared to a calibrated maximum number. If the misfire is excessive, a this DTC will set.

Conditions for Running the DTC

• If start-up ECT temperature is below minus 7°C (20°F), misfire detection is delayed until ECT temperature is more than 21°C (70°F). If start-up ECT temperature is more than minus 7°C (20°F), misfire detection begins after a 5 second delay.
• No active vehicle speed DTCs
• No active TP sensor DTCs
• No active MAF sensor DTCs
• No active camshaft sensor DTCs
• No active crankshaft sensor DTCs
• The fuel level is more than 10 percent
• The system voltage is between 11-16 volts
• The engine speed is between 450-5000 RPM
• The throttle position is steady within 2 percent for 100 ms

Conditions for Setting the DTC
The VCM detects a deceleration in the crankshaft speed characteristic of either an emission type misfire or a catalyst damaging type misfire.

Action Taken When the DTC Sets
If the VCM determines that the engine misfire is significant enough to have a negative impact on emissions, the VCM turns ON the MIL after the misfire has been detected on 2 non-consecutive trips under the same operating conditions. If the misfire is severe enough that catalytic converter damage could result, the MIL flashes while the misfire is present.

Conditions for Clearing the MIL/DTC

• The Control Module turns OFF the MIL after 3 consecutive drive trips when the test has Run and Passed.
• A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the Engine Coolant Temperature is more than 70°C (158°F) during the same ignition cycle).
• Use the scan tool Clear Information function.

Diagnostic Aids
The Misfire Index counts the number of misfires. The scan tool can monitor the Misfire Index. There is a current and history misfire counter for each cylinder. Use the current misfire counter in order to determine which cylinder is misfiring or use the history misfire counter for misfires that are not currently present. Many different conditions could cause an intermittent misfire.

Check for the following conditions:

• Check the IC control circuit for an intermittent short to ground.
• Check the spark plug wires and the coil wire for the following conditions:
• Ensure that the spark plug wires are securely attached to the spark plugs and the distributor cap.
• Check the wire routing in order to ensure that crossfiring is not occurring.
• If the misfire occurs when the weather is damp, the problem could be due to worn plug wires.
• Check for contaminated or a low fuel level and the following conditions:
• Check the fuel condition and quality. Dirty or contaminated fuel could cause a misfire condition. Refer to Alcohol/Contaminants-in-Fuel Diagnosis.
• If the fuel level is low, the fuel pump may draw air into the fuel rail, causing a stumble and possible misfire condition. Check the fuel trim numbers in the freeze frame to determine if this has occurred. It would be likely if the short term fuel number was above +20
• A restricted fuel filter can also cause a misfire.

Sticking intake or exhaust valves on engines with a misfire when cold.

Check HO2S for abnormal voltage readings. Check for a vacuum leak as a possible cause of the engine misfire.

An intermittent may be caused by any of the following conditions:

• A poor connection
• Rubbed through wire insulation
• A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis. See: Powertrain Management\Computers and Control Systems\Testing and Inspection\Symptom Related Diagnostic Procedures

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


5. The misfire is considered random on all cylinders if while viewing the misfire fire counters in the misfire data list, the misfire seems to move to different cylinders.

6. The misfire is considered consistent if the misfire is occurring on the same cylinder(s) consistently.

7. When checking the spark at the spark plug wires, the spark should be consistent. A few sparks then nothing is no spark.

---------- Post added at 02:54 PM ---------- Previous post was at 02:50 PM ----------

you will need to get the misfire history to find out what cylinders are acting up. when you find out the data post it here. if it is likely that the engine has not had ignition parts replaced in the last 100k miles then it is time to do it. if you do use only delco or delphi parts. but you can use autolites for the plugs if you want.