Engine was cleaned and 1 gallon 2cycle mix fuse added mistakenly by the detailer. had codes for both bank 2 o2 sensors, p0300 random misfire and a mass air flow code ... replaced bank 2 upstream sensor and ran on lift, bank 1 upstream sensor flagged. replaced that sensor also and car still misfires badly. removed plugs found all 4 bank 2 plugs black. replaced all spark plugs and still misfires. monitored misfire found #4 and #6 both miss badly. verified wires not crossed. looked in distributor cap for crack between the 2 cylinders, ok. cap worn but no visible cracks and no play in distributor
SOURCE: My 96 GMC sierra has a random misfire
couple of things, did you actually gap the plugs yourselfor did you go on the assumption that they are pre gapped ? are the lead wires all in the correct firing order ? Is it possible a vacuum line got dis-connected ? I would also check the cap and the rotor.
SOURCE: I got 96 chevy c2500 pickup, 5.7 vortec, engine
Check your bank 2 plugs for colour (do they look hot like they running hot ). Check you EGR Exhaust Gas Recirculation valve (looks like a 80mm diameter spaceship with a vacuum line to the top of it) If this remains closed the engine runs very hot and causes misfire. Possible causes are EGR not opening are 1) perforated diaphragm 2) encrusted valve stem 3) clogged exhaust gas feed pipe. A quick check for function: run the engine and remove the vacuum tube. The engine note should change as the tube is connected and then disconnected. Also pushing on the underside of the EGR with your fingers to lift the diaphragm to open the valve should also result in change in engine note. If its not working just disassemble the EGR and clean with carb cleaning spray, also clean the exhaust gas feed pipe likewise.
SOURCE: I have a 1996 chevy c1500 that is throwing a p0300
Look at the plugs, if they looked hot and cooked then the misfire is unlikely to be electrical. If they look OK check out the Cam sensor connections on the edge of the flywheel housing. If the plugs are cooked it could be a duff EGR valve or, because you have no code, a clogged exhaust feed pipe to it. The absence of the introduction of a measured amount of exhaust gas to the mix would give rise to systemic overheating of the ignition temperatures and this in turn can lead to multiple fire events
Generic OBD II Diagnostic Trouble Codes
DTC CODES P0300 to P0399
P0300....Random/Multiple Cylinder Misfire Detected
P0301....Cylinder 1 Misfire Detected
P0302....Cylinder 2 Misfire Detected
P0303....Cylinder 3 Misfire Detected
P0304....Cylinder 4 Misfire Detected
P0305....Cylinder 5 Misfire Detected
P0306....Cylinder 6 Misfire Detected
P0307....Cylinder 7 Misfire Detected
P0308....Cylinder 8 Misfire Detected
P0309....Cylinder 9 Misfire Detected
P0310....Cylinder 10....Misfire Detected
P0311....Cylinder 11 Misfire Detected
P0312....Cylinder 12 Misfire Detected
P0313....Misfire Detected with Low Fuel
P0314....Single Cylinder Misfire (Cylinder not Specified)
P0320....Ignition/Distributor Engine Speed Input Circuit
P0321....Ignition/Distributor Engine Speed Input Circuit Range/Performance
P0322....Ignition/Distributor Engine Speed Input Circuit No Signal
P0323....Ignition/Distributor Engine Speed Input Circuit Intermittent
P0324....Knock Control System Error
P0325....Knock Sensor 1 Circuit (Bank 1 or Single Sensor)
P0326....Knock Sensor 1 Circuit Range/Performance (Bank 1 or Single Sensor)
P0327....Knock Sensor 1 Circuit Low Input (Bank 1 or Single Sensor)
P0328....Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)
P0329....Knock Sensor 1 Circuit Input Intermittent (Bank 1 or Single Sensor)
P0330....Knock Sensor 2 Circuit (Bank 2)
P0331....Knock Sensor 2 Circuit Range/Performance (Bank 2)
P0332....Knock Sensor 2 Circuit Low Input (Bank 2)
P0333....Knock Sensor 2 Circuit High Input (Bank 2)
P0334....Knock Sensor 2 Circuit Input Intermittent (Bank 2)
P0335....Crankshaft Position Sensor A Circuit
P0336....Crankshaft Position Sensor A Circuit Range/Performance
P0337....Crankshaft Position Sensor A Circuit Low Input
P0338....Crankshaft Position Sensor A Circuit High Input
P0339....Crankshaft Position Sensor A Circuit Intermittent
P0340....Camshaft Position Sensor 'A' Circuit (Bank 1 or Single Sensor)
P0341 Camshaft Position Sensor 'A' Circuit Range/Performance (Bank 1 or Single Sensor)
P0342....Camshaft Position Sensor 'A' Circuit Low Input (Bank 1 or Single Sensor)
P0343....Camshaft Position Sensor 'A' Circuit High Input (Bank 1 or Single Sensor)
P0344....Camshaft Position Sensor 'A' Circuit Intermittent (Bank 1 or Single Sensor)
P0345....Camshaft Position Sensor 'A' Circuit (Bank 2)
P0346....Camshaft Position Sensor 'A' Circuit Range/Performance (Bank 2)
P0347....Camshaft Position Sensor 'A' Circuit Low Input (Bank 2)
P0348....Camshaft Position Sensor 'A' Circuit High Input (Bank 2)
P0349....Camshaft Position Sensor 'A' Circuit Intermittent (Bank 2)
P0350....Ignition Coil Primary/Secondary Circuit
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