Error code P300. Have replaced plugs and wires. No other sensor codes. No loss of power and only a slight engine vibration at an idle. Have taken a new coil and installed it on each cylinder with no visible change. Has 103000 miles on it. Air filter is good. It is the 5.3. Strong odor of unburnt fuel at exhaust

 

I'd replace the injectors, or O rings. If you have done the ignition, and smell gas, probably an injector leaking

 

if it where sending a code on a particular cylinder i would agree with you. I am getting a random misfire meaning it bouncing cylinder to cylinder. Im not a mechanic by no means but I would think if I had a bad injector I would get a 301-308 code.

 

have someone with a scan tool view the misfire data. gm has the best misfire counter data. if will show current and historical misfire counters for each cylinder even though the only code is a p0300. Use this data to isolate the misfire to a particular cylinder or bank.

 

I have had three auto parts stores connect to it and all they can tell me Is random misfire. I have looked at programs I can download to my pc. Rather than paying a dealership could i populate the same data on my pc

 

I had a misfire on cylinder 6 and my truck would buck from first gear. The code would be p306. This happen once a month for about six months. I took it to a mechanic and they said the lifter was stuck because the guides had been worn out. They Fixed that and then the same thing happened less than two weeks later. From everything i gathered the real problem was the lobes on the camshaft. This is a 2007 silverado which is probably a similar motor

 

If it were sending a specific code I'd look at that cylinder. Since you have multiple misfires I look at injectors based on your smelling unburned fuel.

 

other than having a scan tool; autoparts store employees have zero training in diagnosing automobiles. Maybe a gas station or car wash attendant can help.


autoenginuity has the software required to access this information from the pcm. Its probably $300 for a gm package. this will do all gm products. You can expand to other makes for a price if you ever buy another brand.

 

fuel smell do not mean the injectors are at fault. it just means there was no combustion event. everything that effects combustion in a cylinder must be checked. spark, fuel, compression, all at the right time.

 

Thanks for all the replies. I checked the fuel pressure this morning and it was 53 with key on and engine off. If it were low compression on a cylinder wouldn't it read at that cylinder and not a random misfire. Any thoughts on what to try next.