P0307 misfire on my 2005 5.3L Silverado

I'm hoping someone can help me here. My 2005 Silverado with a 5.3L CEL came on. I ignored it at first because I had just fueled up a day before. 2 days later the truck was running a little rough at idle, and climbing slight hill the CEL started blinking. Took to dealer for a check. At first they said it was P0300, and did the following: Somehow found cylinder 7 misfiring. Swapped spark plug and wire with cylinder 5, still misfired on #7. Swapped coil pack, still misfire on 7. Cleaned fuel rails and swapped injectors (#5 and #7). Problem still misfiring on #7. Performed vac check, passed. Asked me for more time ($$$) and I said NO, so I could perform a tune-up. Truck has 80K miles, never tuned up yet. Upon doing that, I noticed this truck doesn't have a fuel filter under the driver's seat, or anwhere external to the tank. Damn! CEL light was cleared by dealer. Next day it came back on, and a buddy at work has a scanner. Hooked it up. P0307, cylinder 7 misfire. I am tuning up this weekend, wires, plugs, but no fuel filter.

Anyone have any advice as to what I can check? I hate to just pay for stuff I might be able to check. Thanks in advance!

fuel filter is a part of the fuel pump...another reason why GM sucks..this was changed when they knew the end was near.

your problem maybe the intake manifold gasket leak...very common..
check the fuel regulator for fuel in the vacuum line driverside fuel rail.

you could also have the defective heads, coolant drips into the cylinder[crack]...

it could also be the valves in that cylinder are not working...like a rocker arm broken.. or valve spring...

it could also be the valves in that cylinder are not working...like a rocker arm broken..

Thanx j cat. I appreciate the responses. I'll check this stuff out this weekend. Meanwhile, today, after clearing the P0307 I put a new wire on just #7, and dumped a bottle of injector cleaner in a half full tank of guess. I've driven about 50 miles since, some interstate, and so far so good. But I'll tune-up, and look at the items you mentioned that I am able to. I'm no ASE mechanic.

Thanks again,



Lloyd