Anyone ever get a p0300 random missfire code, cylinders 2,4,6,8 on the passenger side are all misfiring but the drivers side bank is fine. Running out of ideas, has new ac plugs, new ac wires, new fuel filter, checked fuel pressure and its good, new injectors and fuel rail, got a used computer and got it reflashed and nothing, has good compression. So I was thinking the right side cat plugged but it appears to be working on the scan tool and with a temp reader gun. Its missing so bad it sounds like its knocking, any ideas??? The vehicle is a 2002 1500 with a 5.3.

 

My car was acing the same way it was a fuse to the leftbank my cat haze a and b bank so 2 different. Fusesone was burnt so it had no power sounded. Bad replace fuse and good as new

 

check fuses and make sure the coil pack is plugged in

 

The coil pack is plugged in, checked that first. Even swapped some around to no avail, Ill check fuses, any particular one to start with. This is my buddies truck and he's going insane right now lol

 

There should be two fuses, one for each bank, under the hood fuse box, will be marked on the fuse door

 

Try the diagnostics and tuning forum????

 

If you suspect the cat, physically remove the O2 sensor upstream of that cat (i.e. give exhaust a path to exit) and see how engine runs.

 

Logically seems like either a fuse (as mentioned) or wiring issue to that location. Sounds like all other variables have been taken out. If the fuse is good, try testing/visually inspecting the wiring for continuity.

 

my guess is fuse stopped up cat or bad o2 sensor

 

It was a plugged cat on the passenger side, new y pipe and shes happy.

 

Cat or o2 sensor I've seen this before and had it before

 

Could be mechanical engine, but more likely something else. Weird thing with these engines, if you get a misfire on one cylinder it will train down that side. It may be due to improper valve timing which can result in pulses in the intake. Is it running really bad, or just small misfires? If it running really rough, I would pull the rocker cover on that side and double check the valve springs. Could have a broken one.

 

I had same code. just got the car back from having an exhaust put on it.

for kicks, I removed the injectors and cleaned them out like you see on youtube with cleaner and a syringe. code has not returned yet, but I only drove around the block.

 

Are you cammed? This is a common code if so...

 

If that's all you did it will likely rear it's ugly head again.

 

Guarantee you the cat is completely melted drop the y pipe fire it up and see if it's smooth.

 

He fixed it about 5 posts up.

James

 

DOH!

 

glad you got it fixed! In my experience this has been caused by plugged cats also.

 

Yea all fixed, It was a truck not a car, 2002 Silverado 5.3 all stock. It was just the cat, I told him to get new front o2 sensors but he didn't have the money. I took the B1S1 o2 out and it ran better with a breather hole so I told him to get the pipe. Its still making a noise in the valvetrain not sure if its a bad rocker, pushrod or pissy spring but at least it runs good now and has power. Either way I feel good, I told him it was the cat from the beginning but he didn't listen