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2003 silverado 6.0 with misfire.

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  • 2003 silverado 6.0 with misfire.

    I have a 2003 silverado with a misfire. It has a flashing engine light. I checked the plugs wires and coil pack all seem fine. I cleaned the mass air flow sensor. I put fuel treatment in the fuel as well. It has a p0300 code. It reads the cylinders that have misfire is #5 and #6 Can someone please help.

  • #2
    Re: 2003 silverado 6.0 with misfire.

    Have you tried moving around the coil packs to see if the misfire follows the cylinder?

    Otherwise, it could be a number of things. More than likely though it's a clogged cat or something.


    1983 Jimmy Sierra Classic-Future LSX Swap Recipient
    2002 Silverado 2500HD CCSB LT-Daily Driver
    1995 Corsica-Super-Sleeper in Progress

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    • #3
      Re: 2003 silverado 6.0 with misfire.

      These trucks also were fairly notorious for intake leaks. No worries though, its a dry intake setup and the gaskets can be easily changed in an afternoon. Before you get to that point, I would move the coil packs around...See if the miss follows the coils. Also, when was the last time you replaced wires? When does it miss? Idle, driving, both...

      How did you check the plugs, wires and coil packs?
      Last edited by T Man; 03-07-2011, 06:14 PM.
      If you don't have time to do it right, then you don't have time to do it twice.

      01 ECSB 2500HD 4x4 6.0
      250K and runs like a new truck

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      • #4
        Re: 2003 silverado 6.0 with misfire.

        It does it at idle and while under load. I checked the plugs and coil packs and it's always at cylinder 5 and 6. I checked the ohms threw the coil packs and check the wires and plugs

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        • #5
          Re: 2003 silverado 6.0 with misfire.

          do you see any foul play on the plugs?

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          • #6
            Re: 2003 silverado 6.0 with misfire.

            Mine did this this morning on #1 and #3. The valave springs were broke. Being #5 and #6 on two different banks, I doubt its a spring issue though.
            2007 Silverado Classic, Crew Cab, Eagle 079, Magnaflo, Airraid and BB Tune.
            2001 Silverado HD, 6" Rancho Lift, 16x10 Eagle 102's and 36x14.50x16 STS's, Rancho Traction Bars. SOLD

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            • #7
              Re: 2003 silverado 6.0 with misfire.

              The plugs are good. I checked for air leaks it doesnt have any air leaks. Could thisbe cause by truck being straight pipe with mufflers cut out of it? Should I change the injectors or just run some injector cleaner threw there?

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              • #8
                Re: 2003 silverado 6.0 with misfire.

                Originally posted by showntow View Post
                The plugs are good. I checked for air leaks it doesnt have any air leaks. Could thisbe cause by truck being straight pipe with mufflers cut out of it? Should I change the injectors or just run some injector cleaner threw there?
                Have a o1 2500HD with the 6.0 have the same problem changed plugs and wires same thing noticed it does it when its hot or loaded. Dont know what to do hope you can help.

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                • #9
                  Re: 2003 silverado 6.0 with misfire.

                  Ditto.
                  2004 6.0L with P0300 misfire at speeds greater then 60mph. Misfire causes the convertor to come unlocked. Changed air filter, plugs, wires, double dose of fuel injector cleaner, cleaned MAF, checked for intake leaks with starting fluid and still no luck. Have to check fuel pressure. My code scanner says EVAP system is not OK (yellow light vs. green light), so that will be my next thing to look at......

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                  • #10
                    Re: 2003 silverado 6.0 with misfire.

                    Check the FPR. My 99 5.3 (I know its not a 6.0) was throwing a P0300 and flashing check engine light. Come to find out the FPR went ballistic and took out my motor ($3200 for a rebuild).

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                    • #11
                      Re: 2003 silverado 6.0 with misfire.

                      i also have this problem 2000 6.0 changed fpr fuel filter doing plugs and wires tomorrow, mine almost chugs under load sometimes, goes away when u hit the gas. PO300 random missfire my handheld says?
                      Last edited by chevyike; 11-06-2011, 09:38 PM.
                      1996 2 door tahoe 4x4 5.7
                      2000 crew cab 2500 classic shortbed 4x4 5.7
                      1998 GMC sierra reg cab short box 4x4 5.0
                      1993 reg cab stepside 4x4 5.7
                      1995 Tahoe 4dr 3" lift 4x4 5.7
                      2000 silverado 1500 ex cab 4x4 5.3
                      2000 silverado 2500 ex cab 4x4 6.0

                      X-BOX gamertag CHEVYIKE

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                      • #12
                        Re: 2003 silverado 6.0 with misfire.

                        Originally posted by harlan View Post
                        Ditto.
                        2004 6.0L with P0300 misfire at speeds greater then 60mph. Misfire causes the convertor to come unlocked. Changed air filter, plugs, wires, double dose of fuel injector cleaner, cleaned MAF, checked for intake leaks with starting fluid and still no luck. Have to check fuel pressure. My code scanner says EVAP system is not OK (yellow light vs. green light), so that will be my next thing to look at......
                        UPDATE: Couldn't figure it out, but had a few suggestions from a Ford? mechanic to do a crankshaft relearn procedure. Took it to Chevy, they did the re-learn procedure and a firmware update, and they said I was still getting random misfires. They recommended injector clean and throttle body clean (they were having a $ special). I told them I had done a double dose of cleaner in the tank, and they said a better way of doing it was to run it off the bottle A little hesitant about spending the $$$, I said go ahead. The service writer came back and said all done - I said what about the misfires, he said no more. I said I'd be back if there were.....I got an oil change, tire rotation and balance, relearn procedure, firmware update, injector clean, and throttle body clean for $240, and the trucks been perfect!! Benn to NY pulling a boat twice, and the trucks never miss fired, torque convertor never unlocked, and the driveabilty is back to where it once was.

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                        • #13
                          Re: 2003 silverado 6.0 with misfire.

                          Have had the same problems on 03 silverado 1500. Did it the first time after bad storm, seem to have fowled out some plugs. New plugs seemed to fix the problem but never got full power back. Year later engine light came on for a bad bank 1 cat, and o2/ evap systems not ready. checked all coil packs replaced one and bank 1 plugs then cat. Intake manifold had small leak i fixed that as well. Engine light went off on its own and rained a day after repairs and i am back in the same boat rough idle egine light flashing (random misfires) and not even half the power it should have. I have ten different codes now all pointing to TPS, MAF and misfires. Any suggestions?
                          Last edited by (((BASS))); 11-07-2011, 11:33 AM.

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                          • #14
                            Re: 2003 silverado 6.0 with misfire.

                            I am also having an issue with my 2003 2500HD.. I changed the plugs and leads... I have a blackbear EFI live tune and lately I have been checking the log and I am getting missfires all around my cylinders at random times..... Mainly though its cylinders 1, 2, 8. The truck doesnt seem to drive any different and the check engine light only seems to come on occasionally when towing a heavy load, and will flash for a minute and then turn back off.... Anyone have any ideas on this?

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                            • #15
                              Re: 2003 silverado 6.0 with misfire.

                              just an FYI, the flashing light means your in danger of melting your cats if you keep driving.
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                              92 k1500
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                              2006 ECSB 5.3
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