Check Engine Light
 

2010 Camaro V-6
Check engine light goes on after getting on the gas a little. Did come on one time with cruise on the highway. Codes are the generic 300 miss fire codes. The crazy is that it reads a miss fire on all 6 cylinders. Only 18k miles as it has been stored most of the time. Took it in twice to clean injectors and have the same issue. Changed all spark plugs as well. Have our mechanic stumped. Any ideas for the next step?

What to do next? it sounds like nothing has really been done other then throwing some parts at it and hoping. There is a section in the manual for random miss fire codes. As a general rules truly random miss fires come from a fuel issue. That can be causes by any part of the fuel system but it is not impossible that it is coming from the ignition system. The process to track it down will vary from system to system. What I like to do is confirm the O2 sensors are reading accurate then use a data collection system and record all the system sensor while it is missing. This should tell you if its a lean miss or a random spark drop. It may also give you some idea what the problem is. Example: If the MAP sensor readings change then the miss starts. You can learn a lot by just having a scanner hooked up counting Miss fires. You may get data that show cylinder 1 is missing 10X more then the other cylinder. or its the right side of the motor.

If the trouble tree in the manual does not get you answers next the engine needs to go one a engine analyzer/Scope. A scope will not tell you exactly what it wrong but it will tell you the results. Like. Cylinder 1-3-5 are lean. or cylinders 2-4-6 are dropping compression or X number of cylinders are dropping spark when over 20K volts are needed. Once you know for sure what is failing you can go back to the data logs and pin point the issue or set up some new tests to check the components involved.

Just a side note: sitting in storage is really bad for gas and it seems to me like modern gas is even really bad at sitting. Low fuel pressure can cause a random miss fire. You have cleaned the injectors so it could be an at the pump issue. I am sure Fuel pressure test is part of the trouble shooting random miss fires. You would want to do the fuel pressure test while it was missing. This Does not mean go buy a fuel pump. Your fuel could just be too thick and you need a couple of tanks of the good stuff run through with some injection cleaner. It may mean the sock at the bottom of the tanks is plugged. Also plugs are not really effected by age but the tubes degrade with time. Are you getting any oil on the plugs? Again that is just an observations the trouble tree for random miss fires is the way to go.

GM was so keen on their mechanics knowing how to follow a trouble trees (what they use to call their step by step diagnosis ladder) the GM yearly certification test was open book and 90% of the questions required you to follow the step by step procedure. I remember thinking if someone was good at following those trouble trees you could know almost nothing about a car and you could still pass the GM certification test.