Check Engine Light Came On

[2001gmcsierra]

Truck was cutting out when driving for the past week, then I changed the gas I was using and it appeared to get better but today in the morning the check engine light was blinking and now on my way home from work, the check engine light stayed on. I have a feeling it might be the fuel pump but was looking for opinions from this site as to what it could be. The truck is a 2001 GMC Sierra 4x4 with a 4.8L engine

 

Any help is appreciated

[2000DV4.8]

Blinking SES light means misfire.

 

Get the code read, and then come back. If we tried to give you any advice without the code, all we'd be doing is guessing.

[2001gmcsierra]

Will do once I get through to my mechanic, was just wondering whether someone could have any ideas as to what it could be. A buddy just told me that if it was the fuel pump then the truck would not start and teh check engine light would not come on and he said it is most likely the O2 sensors as I recently had O2 sensor extenders put in

[kuhl_530]

I can't imagine the O2s giving a blinking check engine light (which btw is worse than constantly on, or means critical fault). Like stated above, just throwing out what it could be without a code would be reckless, but I just don't think the O2s are the sole cause of the problem.

[2001gmcsierra]

The code is P0303 and the person said it is cylinder 3 misfire....anyone have any ideas?

[2001gmcsierra]

Was just looking at this and it appears this person had the same problem I am having....what do you guys think?

 

http://www.2carpros.com/forum/1994-gmc-sie...sc&start=10

 

Oh and the mechanic turned off the check engine light and after 15 km's of highway driving, it still has not come on

[2001gmcsierra]

I found a very helpful website that lists all of the possible problems but I need help from you guys as to how I could determine the exact problem:

 

Fault Code Definition:

 

Misfire Detected in #3 Cylinder

 

Symptoms:

 

Check Engine Light Flashing

Rough running, hesitation and/or jerking when accelerating

In some unusual cases there are no adverse conditions noticed by the driver

In some cases there may be performance problems, such as dying at stop signs or rough idling, hesitation, misfires or lack of power, especially during acceleration and a decrease in fuel economy

 

Common Problems that Trigger the P0303:

 

Worn out Spark Plugs Ignition Wires, Coil(s), Distributor Cap and Rotor (when applicable)

Incorrect Ignition Timing

Vacuum Leak(s)

Low or Weak Fuel Pressure

Improperly functioning EGR System

Defective Mass Air Flow Sensor

Defective Crankshaft and/or Camshaft Sensor

Defective Throttle Position Sensor

Mechanical Engine Problems i.e Low Compression, Leaking Head Gasket(s) or Valve Problems

 

Common Misdiagnosis:

Fuel Injectors

Oxygen Sensor(s)

Power Train/Drive Train problems

[2001gmcsierra]

does anyone which one is cylinder 3 so I could check the spark plug/wires