Need help! Cylinder 7 Misfire code

[dclonch1]

Ok - here's my problem - some genius on here surely can help!

My Service Engine Soon light came on a few nights ago.
It went on solid, then flashed - to indicate a misfire.

I have a Superchips tuner (my truck is not tuned - i just use it to pull codes)
I ran the DTC's and got P0307 - Fault Cylinder C-Misfire Detected (CYLINDER 7)
SO - I did the following (to no avail)
1. Changed spark plugs --- DID NOT HELP - same code
2. Changed fuel filter --- DID NOT HELP - same code
3. Switched #5 and #7 spark plug wire --- DID NOT HELP - same code
4. Switched #5 and #7 coil --- DID NOT HELP - same code

SO --- now I am stumped. Anyone with any ideas on where to go from here?

Thanks in advance for anyones input.

[Mikado14]

You did not say what year or the type of injection you have. If you have individual injectors (SEFI) I would check the injector on #7 cylinder, assuming that your scanner will do so. If it doesn't, try lifting the fuel rail and swapping the injector with another and see if the misfire follows it.

[dclonch1]

sorry

99 Silverado 5.3

SEFI

[Mikado14]

If your scanner won't read the injector, and even then it would only be the pulse duration, try swapping. It isn't that hard, just a little time and you will know. Or, try running some injector cleaner through the system.

[taxman82]

Had the same problem with my 99 5.3. but on cylinder 2. It was a clog injector took it in and had them cleaned. Two weeks later, (you guessed it) back to the shop for a second cleaning (free of course). It fixed that problem however the truck was a real piece. Switch to a 99 suburban, better ride and for now way more reliable.

[tommie99]

yes mine too its from running low grade fuel in it i pull the fuel rail and it was full to the top with dirt i clean it and reinstalled it because that puppy was 108.00 and there is 8 of them so i take me time and clean it myself works great....tommie99

[skipr]

There's a TSB (technical service bulletin) on the injector poppet valves sticking/ clogging on C/K trucks with CSFI. First time they purge injectors with 150 psi Co2, if it happens a second time they will replace CSFI with a new MFI unit. This extended warranty is good up to 200,000 miles or ten years.The problem is getting the GM mechanic to admitt that the problem is the injectors. You are better off having an independant mechanic do the work and have GM reimburse you for the work.

[spackelman]

Had Similar Problem. 2002hd, 8.1 - # 5 Wire Was Rubbing Against The Steering Shaft. Only Grounded When The Shaft Was In The Exact Position Also Grounded When The Engine Torqued. With Initial Inspection The Wire Did Not Lood Like It Touching Anything. Check All Your Wires Again - Its Worth A Good Look.

[stubbornmike]

It could also be a lower intake manifold leak @ cylinder 7... gm is famous for this....check your water level regularly