Random Misfire p0300 HELP
 

2000 chevy Camaro 3.8 engine. Have had a random misfire code for months, but smog is coming up now no one can figure out how the hell to fix this thing.
I have changed, spark plugs, wires, coils. I bought a new ICM from auto zone and put in it there, and changed all 3 02 sensors. Even put the fuel cleaner in the gas.
Nothing happened, car has to be driven about 40miles before that CEL comes back on. Run the code reader, comes up with p0300.
Car was taken to a shop, they replaced the fuel filter, nothing. They wrote “misfire 65mph under load 180 degrees.”
They also put in a new cam sensor and road tested the car but the light came back on so they put the old cam senor back on.
Took the car to a different shop they did a fuel injector flush. Light came back on after being driven.
After that the guy scanned the code on the computer and found that it was cylinders #1 and #6 misfire. He then did a compression test on 1,3,6. #1=125psi, #3=140psi, #6=140psi.
I am at a loose with this car, the second shop told me that he really has no idea were to go from here, that there is nothing mechanically causing the misfire that he can see. he told me to take it to a chevy dealer to have them diagnose it.
If you have any input on what the hell could be going on I would really appreciate it.
Help me please…. Thank you.

First of all, welcome to the forums!

That's a tough one man, you did just about everything I can think of that would cause that.

Do you get #1 and #6 misfire every time? Does the car run well, or a little rough? How's your gas mileage? Did the mechanic check the electronics on all the injectors? How many miles on your car?

Random misfire is usually caused by a lean fuel mixture, which causes each or all cylinders to misfire at one time or other. Check the fuel pressure, as the fuel pump may be weak and not able to provide enough fuel under load, also check the fuel pressure regulator, and change the fuel filter. The pressure must be tested with a gouge, just checking the pressure by watching fuel squirting from the test valve proves nothing.

That's a tough one.. I would agree with the injectors being checked.. does it idle ok, possible vaccume leak from manifold? Maybe even a bad head gasket that's dripping fluid into cylinder slowly enough to cause a misfire.

First all thanks you so much for the quick reply s!!

THe second shop was going to change a fuel injector before he tested it. Thats when he said he doesnt think thats it. Nice guy didnt want to wast anymore of my money on something that might work. Thats why he told me to go to the dealer to just have them diagnose it.

You really need to check the fuel pressure, bad injectors will not generate the P0300 DTC. A bad injector Will generate a P03x code (x being the cylinder number. Low fuel pressure will make all cylinder misfire at random, and the PCM will then set the P0300 code.
You also mentioned that your mechanic said that cylinders #1 & #6 were misfiring, in this case the PCM would set DTC P0301 and P0306. Since these cylinders aren't fired by the same ignition coil, it would indicate this is not a coil problem, otherwise the coil mate cylinder would also misfire. In this case it could be bad ignition wire or spark plug, or an individual injector. If the wires and plugs are good, then there is a good chance that the injectors are not being fired, or that the injectors are not functioning properly (clogged or not working).