P0300 code why can we fix it?

They are two different items. The knock sensor's job is to keep engine timing at it optimum position, just before you get valve ping. Here is a picture:

Have you tried cleaning the MAF?

Welcome to 2CarPros.

If the fuel trims are that high, something is allowing unmetered air into the engine. How did you check for vacuum leaks? I know you repaired the PCV, but did you check the intake? Also, are there any exhaust leaks pre catalytic converter? Is fuel pressure within spec?

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

I have one other thing I would like for you to review. It deals with issues specific to a random misfire. Read through it and see if it is helpful for you.

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2004 Chevy Truck Silverado 1500 4WD V8-5.3L VIN T
Important Information - PIP 3056
Vehicle ALL Diagnostic Trouble Codes ( DTC ) Testing and Inspection P Code Charts P0300 Important Information - PIP 3056
IMPORTANT INFORMATION - PIP 3056
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.

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Let me know.

Joe

Code 300 is for a random cylinder misfire. That's not a ground issue. Start with spark plugs and wires. You didn't list the engine size or mileage so I can only make generalizations. A flashing Check Engine light indicates the most serious of diagnostic fault codes. It means you're supposed to stop the engine right away because too much raw, unburned fuel is going into the exhaust system where it will burn in the catalytic converter and overheat it.

For the bolt, on cars and trucks they're often odd sizes compared to what you can buy at a hardware store. You're better off getting the right one from a salvage yard.

This is most likly the cause, and the fix is free:

This is a TSB also from Chevy:
Information on Engine Misfire MIL/SES Light Illuminated or Flashing DTC P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308, P0420 or P0430 TECHNICAL SERVICE BULLETIN Reference Number(s): 06-06-04-046, Â Date of Issue: Â September 12, 2006 Related Ref Number(s): 06-06-04-046 ARTICLE BEGINNING

SERVICE INFORMATION If you encounter vehicles that exhibit the above conditions, refer to SI for the appropriate DTC(s) set. If no trouble is found, the cause may be due to an ECM ground terminal that has corroded with rust over time. Inspect the main engine wiring harness ground terminal (G103) for this condition. The wire terminal (G103) attaches either to the front or to the rear of the right side cylinder head, depending on the model year of the Full Size Pickup and/or Utility Trucks. If the ECM ground terminal has been found to be corroded, then follow the service procedure outlined in this bulletin to correct the corrosion issue. Fig. 1: Engine Wiring Harness Ground Terminal Location (2007 Full-Size Pickup and/or Utility Trucks) Courtesy of GENERAL MOTORS CORP. Fig. 2: Engine Wiring Harness Ground Terminal Location (1999-2006 Full Size Pickup and/or Utility Trucks) Courtesy of GENERAL MOTORS CORP. 1. Remove either the nut or bolt securing the main engine wiring harness ground terminal (G103) to the right cylinder head. Refer to the above illustration to determine where the ground is located on the vehicle (1). 2. Remove all rust from the ground terminal, the cylinder head and the retaining nut or bolt. 3. Position the main engine wiring harness ground terminal and install the nut or bolt. Tighten: Tighten the retaining nut or bolt to 16 N.M (12 lb ft). 4. Apply some type of electrical moisture sealant to protect the harness terminal from further corrosion.

Hello,

Direct Trouble Code (DTC) P0300 can be set by a variety of conditions. In the diagrams down below I have included the factory diagnostic troubleshooting guide for DTC P0300 for your vehicle. Please go through this guide and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros

Good evening.

Just to throw another idea at you, check the fuel pressure. That is the most common cause for this code. If the pressure is low, it will cause multiple misfires.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Roy

Hello !!
Cyl #3 and #7 are in the same side..

not next to each other...

On the same side on the distributor cap...
Did you replace the "cap"

How about the spark plugs?

When did you replace them?

Are the correct "heat"?

Did you check the pick-up coil?

could be "missing" at low RPM`s

Let me Know and I`ll be thinking about it..

BTW thanks a Lot for your donation!!

Replace the intake gaskets, not the intake. That should fix your problem. You were getting a MAP code because the engine is sucking unmetered air, more that what the computer thinks should be. Basically, your computer is confused. It is taking the readings from the TP and O2 sensors and says that the intake should be sucking a certain volume of air, based on MAF. When you have an intake leak, it produces a lower vacuum that what the computer thinks it should, making the computer think that the MAP is bad. This also explains the O2 sensor reading (which is lean). The engine is sucking more air than what the computer can compensate for. Hope this helps. If you need any more info, don't hesitate to ask.
Dave