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jwh463

2003 5.3 P0300 Assistance

Question

I have had a P0300 since about August of 2011 94k miles, rough idle, somewhat worse MPG but beyond that it doesn't run bad. It uses no oil between changes and I have never used anything but Mobil One. I occasionally get a P0305. Last August I took it to the local dealer and they wanted to tear down the motor. Their report:" customer states CEL is on, low compression on #5. Misfire on #5, swapped ignition coil, spark plug and plug wire. misfire remained on #5. performed inj. bance test and all inj drop the same. found low compression on #5 125psi cust declined tear-down and inspect"

 

Now with 102K miles, code still there and I can't pass state inspection. The catalyst monitor and Evap Sytem Monitor will not will show ready, I can pass if one of those 2 will show ready. I have a code reader and can reset the P0300 code it it will not reappear unless it idles longer than 3 or 4 minutes.

Now since August I have replaced the follwing:

  • replaced spark plugs & wires (AC OEM all the way)
  • replaced fuel & air filters
  • replaced all coil packs
  • replaced Mass Air Sensor
  • replaced thermostat
  • all four O2 sensors (just this week)

 

I even replaced the ECM (spare ecm store on ebAy ) and nothing changes

 

Running out of ideals with out going ahead and allowing a tear down starting with possible valve spring replacement. Is the code associated with the 2 failed inspection items? I have to get a state inspection to be able to park my truck at work.

 

Ideals?

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Edited by jwh463

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If there's low compression on #5, then there is no other way to correct that other than, at the VERY least, to remove that bank's head.

 

I would do a compression test on my own to verify what the shop has already told you.

Edited by Jsdirt

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If there's low compression on #5, then there is no other way to correct that other than, at the VERY least, to remove that bank's head.

 

I would do a compression test on my own to verify what the shop has already told you.

 

is 125 really low if all others were 145-150?

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That's right on the borderline ... 15% variation. I'd do a leakdown test to see if it's valves or rings. If it's valves, you get out of it "cheap".

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How long has it been since you replaced the o2 sensors? And how far have you driven since the replacement?

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How long has it been since you replaced the o2 sensors? And how far have you driven since the replacement?

 

 

200 miles or so? Does it make a difference?

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Yes it makes a difference. When you clear code it reset all of your monitor. So you have to do what they call a complete drive cycle to reset the monitors. Sometimes it takes for ever to complete a drive cycle. And sometimes it can be done within 40 to 50 miles. It all depends on your driving conditions. It looks like you misfire monitor is OK. Below is a complete GM Drive Cycle Procedure (almost impossible to do unless you have a Dino). That is the reason it takes so long sometimes.

 

 

Inspection/Maintenance (I/M) Complete System Set Procedure

 

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provide an overview of each diagnostic category.

 

Description

The purpose of the Inspection/Maintenance (I/M) complete system set procedure is to satisfy the enable criteria necessary to execute all of the I/M readiness diagnostics and complete the drive cycles for those particular diagnostics. When all I/M monitored diagnostic tests are completed, the I/M System Status indicators are set to YES. Perform the Inspection/Maintenance (I/M) Complete System Set Procedure if any I/M System Status indicators are set to NO.

 

I/M Data List

To determine if the I/M readiness diagnostic tests can be run this ignition cycle, use a scan tool to observe the I/M monitor enabled parameters in the I/M Data List.

 

Conditions for Meeting a Cold Start

• The ignition voltage between 11-18 volts.

• The barometric pressure (BARO) is more than 75 kPa.

• The start-up engine coolant temperature (ECT) is between 4-30°C (39-86°F).

• The start-up intake air temperature (IAT) is between 4-30°C (39-86°F).

• The difference between the IAT and the ECT is less than or equal to 6°C (10.8°F)

• The ambient air temperature is between 4-30°C (39-86°F).

• Fuel level is between 15-85 percent

• Without RPO LMG--The fuel alcohol content is less than 15 percent.

• With RPO LMG--The fuel alcohol content is less than 87 percent.

 

Circuit/System Verification

Review the Inspection/Maintenance (I/M) System Status indicators with a scan tool. All I/M System Status indicators should report YES.

 

Inspection/Maintenance (I/M) System Set Procedure

Important: Whenever the ignition is turned ON, ignition positive voltage is supplied to the heated oxygen sensor (HO2S) heaters. After verifying the enable criteria, turn OFF the ignition for approximately 5 minutes to allow the sensors to cool before continuing with the test. Once the engine is started, do NOT turn the engine OFF for the remaining portion of the set procedure.

1. Ensure that the vehicle meets the conditions for a cold start listed above.

⇒ If the evaporative emission (EVAP) I/M System Status indicator displays NO, perform the EVAP Service bay test if available.

⇒ If the EVAP Service bay test is NOT available, it may take up to 6 drive cycles, with up to 17 hours between drive cycles, for the EVAP I/M System Status indicator to transition to YES.

⇒ If the O2S Heater System Status indicator displays NO, ensure that the ignition has been turned OFF for at least 10 hours.

2. Set the vehicle parking brake and ensure the vehicle is in park for automatic transmission or neutral for manual transmission.

3. Turn OFF all accessories; HVAC system, other electrical loads, including aftermarket/add-on equipment, etc.

4. Start and idle the engine for at least 2 minutes and until 65°C (149°F) is achieved.

5. Run the engine for 6.5 minutes within the following conditions:

• MAF parameter between 4-30 g/s

• Engine speed steady between 1000-3000 RPM

6. Return the engine to idle for 1 minute.

7. Apply and hold brake pedal, and shift to Drive for automatic, or apply clutch pedal for manual and operate the vehicle within the following conditions for 2 minutes:

• Depress the accelerator pedal until TP Sensor angle is more than 2 percent.

• MAF signal between 15-30 g/s

• RPM steady between 1200-2000 RPM

 

Important: Do NOT touch the accelerator pedal during the idle period. A change in TP Sensor angle or an increase in engine speed may invalidate this portion of the test.

 

8. Release the accelerator pedal and shift the vehicle to Park for automatic, or Neutral and release clutch pedal for manual, and allow the engine to idle for 2 minutes.

9. Quickly depress the accelerator pedal until TP Sensor Angle is more than 8 percent and return to idle, repeat 3 times.

10. Allow engine to idle for at least 2 minutes.

11. Release the parking brake and drive vehicle at 24 km/h (15 mph) or slower for 2 minutes.

12. Continue to drive the vehicle for at least 5.5 miles between 45-112 km/h (28-70 mph) with the vehicle reaching at least 80 km/h (50 mph).

13. Release the accelerator pedal for at least 2 seconds. This will allow the vehicle to enter decel fuel cut-off.

14. Depress the accelerator pedal until the TP Sensor angle is increased 3-20 percent and maintain a safe speed for 1 minute.

15. Safely stop the vehicle, with the engine in drive for automatic or in neutral with the clutch pedal depressed and parking brake applied for manual, idle for 2 minutes.

16. Shift to Park for automatic and apply the parking brake, or neutral and release clutch pedal for manual.

 

Important: Do NOT disturb the vehicle or turn ON the ignition until told to do so. Disturbing the vehicle may invalidate this portion of the test.

 

17. Turn OFF the ignition and exit the vehicle. Do NOT disturb the vehicle for 45 minutes.

18. Observe the Inspection/Maintenance (I/M) System Status with a scan tool. All of the I/M System Status indicators should display YES.

⇒ If the EVAP I/M System Status indicator displays NO turn OFF the ignition for 17 hours, ensure that the vehicle meets the conditions for a cold start, and repeat steps 12-18 six more times, or until the EVAP I/M System Status indicator transitions to YES. If the indicator continues to display NO, refer to the Inspection/Maintenance (I/M) System DTC Table to identify the DTCs that did not run. Follow the Conditions for Running the DTC in order to set the EVAP I/M System Status indicator

⇒ If any of the I/M System Status indicators display NO, refer to the Inspection/Maintenance (I/M) System DTC Table for the indicator which did not display YES. The I/M System DTC Table identifies the DTCs associated with each I/M System Status Indicator. Follow the Conditions for Running the DTC in order to set the associated status indicator.

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Got to love OBD-II .... :nonod:

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well that drive cycle was done (what a PIA) and still no change. I put it in the shop today, they called and let me know that compression is even on all cylinders and no drop on #5 like dealer reported previusly. The valve springs are all intact and tight. They are now inspecting cam lobes and suspect it or the exhaust valves being bad. I hope to know more after lunch

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If compression is good, I would ask why they are checking the cam or exhaust valves?

 

No need for that if compression is good .... :dunno: .

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If compression is good, I would ask why they are checking the cam or exhaust valves?

 

No need for that if compression is good .... :dunno: .

 

 

Vacuum pressure is very low? That's what I was told

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Probably vacuum leaks, just going by the condition of GM's underhood rubber products I've seen manufactured the past 15 years or so ... If you don't have a big, aftermarket cam. Ignition timing could be another cause ... but less likely with these newer vehicles.

 

If compression & leakdown are good, then the engine is mechanically sound (timing chain, crank bearings, etc. notwithstanding).

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Probably vacuum leaks, just going by the condition of GM's underhood rubber products I've seen manufactured the past 15 years or so ... If you don't have a big, aftermarket cam. Ignition timing could be another cause ... but less likely with these newer vehicles.

 

If compression & leakdown are good, then the engine is mechanically sound (timing chain, crank bearings, etc. notwithstanding).

 

 

cam lobes/lopes? are worn, the valves in #4 and %5 arent working properly. Due to labor costs of just those repairs they are ordering a used 5.3 from a local vendor. I have asked for a breakdown on 5.3 vs 6.0. My wallet is sad

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Yep - that'll do it too. Sorry to hear that.

 

I've said it before & I'll say it again - I'll never buy another GM built after '72. :nonod:

 

And if we lived in a normal world again, you could just keep driving what you have until it's dead. Thank the EPA for your empty wallet ...

Edited by Jsdirt

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...and why did the lobes wear??? There are sooo many members here that have easily hundreds of thousands of miles on their trucks without seeing that problem. Also new valves and a camshaft replacment cost MORE than a USED engine replacement? I must be out of touch with the cost factor of these trucks/engines....

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Can thank GM for that - miles of wiring, multiple intake manifolds, no room to work - takes you couple hours just to get in there. Replacing it is the easy part.

 

If you bought that used maybe the previous owner never changed the oil. If it's been taken care of, then chalk another faulty part out to GM trying to save a buck. Same reason we have Youtube videos of trucks with 500 miles smoking out their garages.

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