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2003 chevy silverado 2500: 6.0 liter..p300..code multi random misfire

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2003 chevy silverado 2500 6.0 liter i keep getting po300 code multi random misfire.. any suggestions?
Submitted: 8 years ago.
Category: Chevy
Expert:  Carhelp4u replied 8 years ago.
How many miles are on this vehicle? Has it had any tune ups? Any work to repair this problem?
Customer: replied 8 years ago.
Reply to carhelp4uhere's Post: 150,000 miles, we have changed #3 coil, plugs, wires etc
Expert:  Carhelp4u replied 8 years ago.
Ok have you been able to verify if this missfire is across all cylinders or if it is contained to just a few? This would be done with a missfire counter on a class 2 scan tool.
Customer: replied 8 years ago.
Reply to carhelp4uhere's Post: we have been told that there is a broken motor mount, would this cause this? the check engine light flashes and then the truck skips for a little bit, the light goes out and the truck runs fine... never occurs at any specific time
Expert:  Carhelp4u replied 8 years ago.
I would not figure the motor mount would have any affect on this one. The big problem here is that we are unsure if this is a missfire on all cylinders or just one. The P0300 is somewhat of a generic code as it does not actually tell you if this is one particular cylinder or 3 cylinders or even all cylinders. There is alot to take in account if you do not have the proper test equipment. We need to verify that there is good clean spark at all cylinders. We also need to verify that all cylinders have good compression. This would be just the basics. There are many things that can cause a missfire. Fuel injector issues, low fuel pressure, vacuum leaks, partially blocked exhaust, and engine grounding problems would be the more common ones. These engine have had a decent amount of problems with the fuel injectors and intake gasket failures, both of which can cause the symptoms you are mentioning. We really need to verify how many cylinders are in fact missfiring, as I stated, you need a class 2 scan tool to verify this through a missfire counter. This will eliminate the guess work on what cylinder are being problematic. Feel free to contact me with any questions! Good luck!
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