P0300 code random misfire...
P0300 is the catch all misfire DTC. There is also 301 thru 308 which designate a specific cylinder. 300 doesn't point to any specific cylinder so you have some extra troubleshooting to do. I would tend to look for something that is common to all 8 cylinders simply because it is the 300 and not 301 to 308. Have you tried looking up the P0300 in Mitchell or Alldata? The GM shop manual also has a detailed truth table type chart for each DTC.
where in NJ are you located?
best bet is to have someone with HP tuners scan missfire events or history on every single cylinder, also check AFR, and see if youre getting any knock.
This will help lead you in the right direction in regards to corrective action.
best bet is to have someone with HP tuners scan missfire events or history on every single cylinder, also check AFR, and see if youre getting any knock.
This will help lead you in the right direction in regards to corrective action.
On The Tree
Joined: Apr 2005
Posts: 192
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From: S. Philly
These are things to check suggested by the manuals:
1. 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.
2. 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.
3. Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.
4. 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.
5. Bad Catalytic Converter.
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the 3-way catalytic converter. The malfunction indicator lamp (MIL) will flash if converter-damaging conditions are present.
1. 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.
2. 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.
3. Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.
4. 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.
5. Bad Catalytic Converter.
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the 3-way catalytic converter. The malfunction indicator lamp (MIL) will flash if converter-damaging conditions are present.
Originally Posted by wildmouse
Are you sure the shake at 70 mph is the engine ? Or could it possibly be tire or drive line related.
Good luck,
wildmouse
Good luck,
wildmouse
Originally Posted by LS1Cobra
These are things to check suggested by the manuals:
1. 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.
1. 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.
2. 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.
3. Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.
5. Bad Catalytic Converter.
Items 2,3,4and 5 are possible causes, but #1 is doubtful in that a single injector is unlikely to cause the whole bank to misfire. It would have to feedback thru the full length of the fuel rail and down into the other individual injector in order to do that. That's a stretch. How about a loose exhaust part or something else hitting the chassis. These are things you check only after you have gone over the engine thoroughly.
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Verdad Gallardo On The Tree
Joined: Apr 2005
Posts: 192
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From: S. Philly
If you ruled out everything then here is another one. I've read in the manual somewhere that it said a bad torque converter will cause the misfire also. For some reason I can't open up my software at home so I can't find the info.
Originally Posted by LS1Cobra
If you ruled out everything then here is another one. I've read in the manual somewhere that it said a bad torque converter will cause the misfire also. For some reason I can't open up my software at home so I can't find the info.
I was getting the misfire code after I had my ASP Pulley installed. Since I had my Predator updated ,I was able to remove the code and a bunch of other codes as well. Maybe you need to check your crank pulley. Just a suggestion. I hope you find what the problem is. Good luck .
The CKP and CMP report the cylinder fire rate activity to the PCM at a rate that is proportional to the RPM. If the rate at which these pulses are reported to the PCM is disturbed (above a minimal threshold value) by say a loose motor mount, loose header bolts, etc. the PCM could misinterpret it as engine misfire. The PCM doesn't know what is causing an erratic pulse rate from the CKP or the CMP it just knows there is one and interpretes it as misfire. Usually the P0300 code comes up right after a camshaft upgrade when at idle there is greater engine lope caused by a lower LSA, but if the cam has not been recently changed something else is the cause. If I got P0300 after installing a underdrive pulley it would lead me to suspect the pulley has caused the engine to be out of balance and simply raising the threshold for the misfire DTC or deleting it altogether does not solve that problem. For a lopy cam you could raise the threshold, but not so high that an actual misfire at some later date is not even detected. All kinds of things cause misfires. Engines misfire all the time. That's normal, but not at a rate that is high enough to set the P0300 thru P0308 DTC.
Originally Posted by eallanboggs
The CKP and CMP report the cylinder fire rate activity to the PCM at a rate that is proportional to the RPM. If the rate at which these pulses are reported to the PCM is disturbed (above a minimal threshold value) by say a loose motor mount, loose header bolts, etc. the PCM could misinterpret it as engine misfire. The PCM doesn't know what is causing an erratic pulse rate from the CKP or the CMP it just knows there is one and interpretes it as misfire. Usually the P0300 code comes up right after a camshaft upgrade when at idle there is greater engine lope caused by a lower LSA, but if the cam has not been recently changed something else is the cause. If I got P0300 after installing a underdrive pulley it would lead me to suspect the pulley has caused the engine to be out of balance and simply raising the threshold for the misfire DTC or deleting it altogether does not solve that problem. For a lopy cam you could raise the threshold, but not so high that an actual misfire at some later date is not even detected. All kinds of things cause misfires. Engines misfire all the time. That's normal, but not at a rate that is high enough to set the P0300 thru P0308 DTC.
Maybe the car just doesn't like these plug wires. I was thinking about getting anotehr set of the wires that were on it when I bought it along w/yet another set of plugs & changing them again & then if it still has the misfire I'll drive it off a cliff. 
compression check do a compression test.if it were a bad o2 you would get a o2 code.a dirty maf sets a code also.have the compression test done.possible broke valvesping,blown head gasket,burned valve.this may save alot of guess work and$$$$.autozones scanner only shows dtcs.take it to a garage or dealership and they can narrow it down a little more,good luck
Originally Posted by NewCar
Maybe the car just doesn't like these plug wires. I was thinking about getting anotehr set of the wires that were on it when I bought it along w/yet another set of plugs & changing them again & then if it still has the misfire I'll drive it off a cliff.
Originally Posted by NewCar
Maybe the car just doesn't like these plug wires. I was thinking about getting anotehr set of the wires that were on it when I bought it along w/yet another set of plugs & changing them again & then if it still has the misfire I'll drive it off a cliff.
Originally Posted by NewCar
Does anyone think I should even bother w/this idea?
Seriously, I think your best bet is to pull the valve covers, look at the springs, and then do a compression test. If you can borrow a tester (maybe the Zone rents them out, dunno) it won't cost you anything and only takes about an hour. Heck, while you are pulling the plugs for the compression test, drop some new ones in if you have them.