HELP! 1999 CHEVY 5.3 SILVERADO P0300

jcj02 · March 3, 2006

1999 chevy silverado z71

5.3 motor

P0300 CODES MISFIRE

MISFIRE ON MOST CYLINDERS

MISFIRE ON #3 CYLINDER VERY BAD

CHANGED PLUGS, WIRES, FUEL FILTER

CHECKED EGR VALVE, NOT BAD

CHECKED FUEL PRESSURE LITTLE LOW

AT SOMETIMES 48LBS BUT THEN HOLDS AROUND 55 AT IDLE WHICH IS FINE

THE PROBLEM!!!

MY TRUCK IS HARD TO START, HAVE TO GIVE IT A LITTLE GAS

WILL NOT STAY STARTED WITHOUT BEING ON THE GAS OR IF IT DOES

IDLES AT 300 OR 500 RPMS

VERY ROUGH IDLE! SHAKING A LOT

ABOUT TO CHECK THE CONVERTERS

ALSO WOULD THE CRANK SENSOR BE A PROBLEM. JUST ANY HELP PLEASE

DOING DISASTER RELIEF 700 MILES FROM HOME, NO PAY AND NO WAY HOME

PLEASE ANYTHING WOULD BE GREATLY APPRECIATED

bobcat5544 · March 3, 2006

if you leave the fuel pressure gauge on it over night does the pressure drop down if it does the it is either fuel pressure regulator or fuel pump. 5.3l fuel pressure reg is know for going bad...

the crank sensor is also the other most likely problem...

jcj02 · March 3, 2006

if you leave the fuel pressure gauge on it over night does the pressure drop down if it does the it is either fuel pressure regulator or fuel pump. 5.3l fuel pressure reg is know for going bad...

the crank sensor is also the other most likely problem...

<{POST_SNAPBACK}>

TRUCK HAS AROUND 160K MILES

IF THE CRANK SENSOR WERE BAD WOULDN'T IT JUST NOT RUN AT ALL??

ALSO ON THE SCANNER IT READ #3 CYL WAS REALLY MISFIRING BUT ALL CYLINDERS WERE ACTING UP.

JUST A LITTLE MORE INFO

ALSO NOT ABLE TO LEAVE THE GUAGE ON OVERNITE

CONVERTERS NOT POSSIBLE??

bobcat5544 · March 3, 2006

yes and no, read below

The Camshaft Position sensor is mounted through the top of the engine block at the rear of the valley cover. The CMP sensor works in conjunction with a 1X reluctor wheel on the camshaft. The reluctor wheel is inside the engine immediately in front of the rear cam bearing. The PCM provides a 12 volt power supply to the CMP sensor as well as a ground and a signal circuit.

The Camshaft sensor determines whether a cylinder is on a firing stroke or on an exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 1X signal in combination with the Crankshaft Position sensor 24X signal in order to determine crankshaft position and stroke. This diagnostic for the Camshaft Position sensor checks for a loss of Camshaft Position sensor signal.

Observe that as long as the PCM receives the Crankshaft Position sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.

jcj02 · March 4, 2006

yes and no, read below

The Camshaft Position sensor is mounted through the top of the engine block at the rear of the valley cover. The CMP sensor works in conjunction with a 1X reluctor wheel on the camshaft. The reluctor wheel is inside the engine immediately in front of the rear cam bearing. The PCM provides a 12 volt power supply to the CMP sensor as well as a ground and a signal circuit.

The Camshaft sensor determines whether a cylinder is on a firing stroke or on an exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 1X signal in combination with the Crankshaft Position sensor 24X signal in order to determine crankshaft position and stroke. This diagnostic for the Camshaft Position sensor checks for a loss of Camshaft Position sensor signal.

Observe that as long as the PCM receives the Crankshaft Position sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.

<{POST_SNAPBACK}>

OK SO WOULD YOU THINK THE CRANK SENSOR IS ANOTHER GOOD POSSIBILITY THAT SHOULD NEXT BE OBSERVED OR WHAT?

SORRY DONT KNOW A GREAT DEAL ABOUT THESE MOTORS MAN BUT I SURE DO APPRECIATE THE INFO I KNOW MUCH MORE NOW

jcj02 · March 4, 2006

yes and no, read below

The Camshaft Position sensor is mounted through the top of the engine block at the rear of the valley cover. The CMP sensor works in conjunction with a 1X reluctor wheel on the camshaft. The reluctor wheel is inside the engine immediately in front of the rear cam bearing. The PCM provides a 12 volt power supply to the CMP sensor as well as a ground and a signal circuit.

The Camshaft sensor determines whether a cylinder is on a firing stroke or on an exhaust stroke. As the camshaft rotates, the reluctor wheel interrupts a magnetic field produced by a magnet within the sensor. The sensors internal circuitry detects this and produces a signal which the PCM reads. The PCM uses this 1X signal in combination with the Crankshaft Position sensor 24X signal in order to determine crankshaft position and stroke. This diagnostic for the Camshaft Position sensor checks for a loss of Camshaft Position sensor signal.

Observe that as long as the PCM receives the Crankshaft Position sensor 24X signal, the engine will start. The PCM can determine top dead center for all cylinders by using the Crankshaft Position sensor 24X signal alone. The Camshaft Position sensor 1X signal is used by the PCM to determine if the cylinder at top dead center is on the firing stroke, or the exhaust stroke. The system attempts synchronization and looks for an increase in engine speed indicating the engine started. If the PCM does not detect an increase in engine speed, the PCM assumes it incorrectly synchronized to the exhaust stroke and re-syncs to the opposite cam position. A slightly longer cranking time may be a symptom of this condition.

<{POST_SNAPBACK}>

OK SO WOULD YOU THINK THE CRANK SENSOR IS ANOTHER GOOD POSSIBILITY THAT SHOULD NEXT BE OBSERVED OR WHAT?

SORRY DONT KNOW A GREAT DEAL ABOUT THESE MOTORS MAN BUT I SURE DO APPRECIATE THE INFO I KNOW MUCH MORE NOW

<{POST_SNAPBACK}>

READ LAST POST AS WELL

UPDATED I WANTED TO LET EVERYONE KNOW THAT THERE IS ALSO A P0400 CODE COMING UP. IT IS THE EVAP CODE I FIGURED IT WAS JUST THE FUEL VENT BECAUSE IT IS HARD TO PUMP FUEL INTO

THANKS AGAIN

GM-Tech · March 4, 2006

If it wasn't already mentioned, I'd be looking real close at the fuel pressure regulator. Lots of them leak.

bobcat5544 · March 6, 2006

ok if you have a P0400 and a P0300...check the mass air flow sensor. that is the most come problem with both those codes is dtc info below

DTC P0400 Exhaust Gas Recirculation (EGR) System Performance

Refer to Emission Hose Routing Diagram

Circuit Description

The PCM operates a PWM solenoid to control the EGR valve. This solenoid is normally open. By providing a ground path the PCM energizes the solenoid which then allows vacuum to pass to the EGR valve. During normal operation, the PCM compares its desired MAF signal with the measured MAF signal and makes corrections in the duty cycle accordingly.

Conditions for Running the DTC

The PCM performs this DTC diagnostic continuously.

Baro greater than 75 kPa.

The DTCs P0405, P0406, P0102 and P0103 are not set.

MAF value is greater than or equal to 0.1484 g/cyl.

Conditions for Setting the DTC

Lowest achieved EGR pressure at full EGR is less than look up table value (internal to PCM)

All diagnostic set conditions met for 2 seconds.

Action Taken When the DTC Sets

The PCM will shut down the EGR.

The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

The PCM will turn the MIL off after three consecutive trips without a fault condition.

A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures

The use of a scan tool.

Diagnostic Aids

The most likely cause of failure is a restricted vacuum line from the EGR valve to the vacuum tee (including the vacuum tee).

To run the diagnostic test the engine must be at the operating temperature, vehicle in drive at idle for approximately 1 minute. Then, with the vehicle in park, hold the engine rpm steady between 1500 and 2100 rpm for 30 seconds. If the diagnostic test fails to run, the vehicle must be driven.

The Adaptive Learn Matrix (ALM) is used to adjust the EGR vacuum control based on mass air flow (MAF). The ALM may change as a result of back pressure increases over the life of the vehicle or other engine system variations. The ALM is made up of sixteen cells (numbered from zero to fifteen) in which each cell covers a range of engine speed (RPM) and load (mm3).

----------------------------------------------------------------------------------------------

DTC P0300 Engine Misfire Detected

Refer to Engine Control Schematics Power, Ground, and DLC .

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 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 in 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, this diagnostic trouble code (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 malfunction indicator lamp (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 or 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. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.

Use a scan tool in order to clear the DTCs.

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 in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

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

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.

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

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

jcj02 · March 6, 2006

ok if you have a P0400 and a P0300...check the mass air flow sensor. that is the most come problem with both those codes is dtc info below

DTC P0400 Exhaust Gas Recirculation (EGR) System Performance

Refer to Emission Hose Routing Diagram

Circuit Description

The PCM operates a PWM solenoid to control the EGR valve. This solenoid is normally open. By providing a ground path the PCM energizes the solenoid which then allows vacuum to pass to the EGR valve. During normal operation, the PCM compares its desired MAF signal with the measured MAF signal and makes corrections in the duty cycle accordingly.

Conditions for Running the DTC

The PCM performs this DTC diagnostic continuously.

Baro greater than 75 kPa.

The DTCs P0405, P0406, P0102 and P0103 are not set.

MAF value is greater than or equal to 0.1484 g/cyl.

Conditions for Setting the DTC

Lowest achieved EGR pressure at full EGR is less than look up table value (internal to PCM)

All diagnostic set conditions met for 2 seconds.

Action Taken When the DTC Sets

The PCM will shut down the EGR.

The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.

The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MIL/DTC

The PCM will turn the MIL off after three consecutive trips without a fault condition.

A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures

The use of a scan tool.

Diagnostic Aids

The most likely cause of failure is a restricted vacuum line from the EGR valve to the vacuum tee (including the vacuum tee).

To run the diagnostic test the engine must be at the operating temperature, vehicle in drive at idle for approximately 1 minute. Then, with the vehicle in park, hold the engine rpm steady between 1500 and 2100 rpm for 30 seconds. If the diagnostic test fails to run, the vehicle must be driven.

The Adaptive Learn Matrix (ALM) is used to adjust the EGR vacuum control based on mass air flow (MAF). The ALM may change as a result of back pressure increases over the life of the vehicle or other engine system variations. The ALM is made up of sixteen cells (numbered from zero to fifteen) in which each cell covers a range of engine speed (RPM) and load (mm3).

----------------------------------------------------------------------------------------------

DTC P0300 Engine Misfire Detected

Refer to Engine Control Schematics Power, Ground, and DLC .

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 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 in 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, this diagnostic trouble code (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 malfunction indicator lamp (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 or 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. A warm-up cycle occurs when the coolant temperature has risen 22°C (40°F) from the startup coolant temperature and the engine coolant reaches a temperature that is more than 70°C (158°F) during the same ignition cycle.

Use a scan tool in order to clear the DTCs.

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 in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

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

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.

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

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

<{POST_SNAPBACK}>

NEW MECHANIC SAID VALVE COVER OR VALVE COVER GASKET? HOW POSSIBLE DOES THIS SOUND?

THANKS J

bobcat5544 · March 6, 2006

not possible

GM-Tech · March 7, 2006

NEW MECHANIC SAID VALVE COVER OR VALVE COVER GASKET? HOW POSSIBLE DOES THIS SOUND?

You sure you understood him correctly? I don't see any way a valve cover and/or its gasket could cause your problem.

jcj02 · March 7, 2006

NEW MECHANIC SAID VALVE COVER OR VALVE COVER GASKET? HOW POSSIBLE DOES THIS SOUND?

You sure you understood him correctly? I don't see any way a valve cover and/or its gasket could cause your problem.

<{POST_SNAPBACK}>

sorry meant intake or intake gasket

jcj02 · March 7, 2006

NEW MECHANIC SAID VALVE COVER OR VALVE COVER GASKET? HOW POSSIBLE DOES THIS SOUND?

You sure you understood him correctly? I don't see any way a valve cover and/or its gasket could cause your problem.

<{POST_SNAPBACK}>

sorry meant intake or intake gasket

<{POST_SNAPBACK}>

Also remember have to give it some gas in order for it to start, will not start by just cranking.

GM-Tech · March 7, 2006

Also remember have to give it some gas in order for it to start, will not start by just cranking.

<{POST_SNAPBACK}>

Totally false. This may have been the case back in the day of carburetors, but those days are long gone. GM's fuel injected vehicles start fine, and probably even better, but not touching the gas pedal at all during a start.

And yes, a leaking intake gasket could cause a misfire.