mo_bird

Ok I need help. Have had a P0307 code for awhile, Already replaced distributor, wires, plugs, coil. Going to do a fuel pressure test tomororw. What else could cause this?

hanky

From the code provided, there is a problem limited to one particular cylinder.
Believe a fuel pressure test will not provide the answer since fuel press affects all cyls.
Would be more helpful if checks / tests were confined to what affects that cyl only.

oilcanhenry

Heres is a good guide on your issue:

• Bad Spark Plugs– Spark plugs are one of the most common causes of P0307. Take a look at the electrodes and see if they are in good shape. Most vehicles now come with iridium plugs that need changed very infrequently. That being said, the plugs are a great place to start. Here’s a great video on how to see if a
  spark plug is bad.
  Chevy Silverado Spark Plugs
  Chevy Silverado Spark Plugs
  .
• Spark Plug Wires– On most modern engines, the plug wires are not nearly as long as they once were, but they can still go bad. Here’s
  how to tell if your plug wires are bad
  (video).
• Coil Packs– Coil packs rarely go bad, but when they do, they can certainly cause P0307 in your Chevy Silverado. Replacing a set can be very expensive. Here’s how to test them.
• Vacuum leak– If your Silverado has a vacuum leak, it can be very difficult for it to get the right air/fuel mixture. This will cause the cylinders to misfire and it’ll throw the P0307 if the leak is around that specific cylinder on the intake manifold. It’s easy (and kind of fun) to chase one down. Popular Mechanics: How to find a vacuum leak.
• Cam or Crank Sensors– This one is very unlikely, but it does happen. If the ECU is not getting the right signal from these sensors, the vehicles timing is not going to sync up and it’ll misfire.
• Low Compression– If you have a leaking head gasket, bent valve, cracked head, etc.. that would cause compression to not be as high as it should, you’re going to get P0307. You should also feel the vehicle is down on power as well.

You really need to get this repaired as you will damage the catalytic converter if you don't. I would definitely run a compression test on
your # 7 cylinder, or all of them. They should be within 15 percent or less from each other and anything lower than 140 PSI is suspect.

It just had to be in the back of your motor, right?