My 2007 Chevy Suburban XLT started running very rough at an idle and shifting rough from 1st to 2nd. Put it on code reader and got a couple of code, 0304 was one, 4th cylinder misfire I have changed the plug, which was really gummed up, new coil and cleared codes. Put injector cleaner in it and have driven at least a 100 miles, with no results, engine light still flashing when driving. Can anyone tell me what else to try.

 

What were the other codes? Might be a clue there.

 

i quick and easy thing is to check your grounds. besides telling us what the codes are

 

These are all the codes:
P0300
P0304
P0521
P0327
P0449
P0521
sorry didn’t have them at the time that I sent the first message.

 

P0300 - general code indicating a misfire. P0304 - cylinder #4 has a misfire.

P0521 - Engine Oil Pressure Sensor/Switch Range/Performance
Symptoms -Symptoms of a P0521 DTC may include: Oil pressure gauge reading low or high Oil pressure indicator lamp illuminatedCauses - Potential causes of a P0521 code include: Low oil level in the engine
Old dirty oil (overdue for an oil change)
Low oil pressure
Faulty wiring or connection/connector in the oil pressure sender circuit
Faulty oil pressure sender/sensor

P0327 - Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor)
Causes - Potential causes for a P0327 DTC include (but are not limited to): The knock sensor is faulty and needs to be replaced There is a wiring open/short/fault in the knock sensor circuit The PCM/ECM has failedPossible Solutions - Verify the resistance of the knock sensor (compare it to factory specs)Inspect for broken/frayed wires leading to the sensorCheck the wiring and connections leading to/from the knock sensor and PCM/ECMVerify proper voltage is reaching the knock sensor (e.g. 5 volts) Verify proper grounding of sensor and circuitReplace the knock sensorReplace the PCM/ECM

P0449 - Evaporative Emission Vent Valve Solenoid Malfunction

Possible causes

• Vacuum leaks, damaged hoses or improper routing
• EVAP system
• Check fuel cap, canister, valves or components
• Faulty purge or vent solenoids
• Check connector and wiring
• Fuel saturated vapor canister
• Failed EVAP vent solenoid

With that many codes all at once I agree with checking the grounds. They may have a common fault.

 

check the ones that connect engine to the firewall also. even if you take them apart and clean the contact you might see corrosion on the terminals or broken ground straps. if you see any thats not in good condition try replacing them