P0307 comes and goes on silverado 3500

[uspres2020]

I have a 2001 chevy silverado 3500 6L gasoline engine. I have been getting a P0307 random multiple misfire #7 on and off for a few months now, occasionally the P0300. Check engine light comes on when I am going up hills, often under heavy load and sometimes when the truck is cold in the morning and the truck starts to run rough until the code clears, which it does pretty quickly usually. I have replaced coil, crank sensor, cam sensor, fuel injectors. Can't figure out what is causing this problem. If I unplug the battery over night the code will be cleared and the truck will be running just fine the next day.

Any suggestions would be appreciated.

[maxwedge]

Anything in the ign system can also cause this a full scan under the misfire conditions will point to which cylinder actually shows the miss use misfire counts.. wires, plugs are the usual suspects. I have had coil wires fail on these engine this can cause 0300, not usually one cylinder. Make sure you have proper fuel pressure also, 58-62 psi.

[wafrederick]

Check for vacuum leaks and around the intake gasket area too.The 6.0s including the 4.8 and 5.3s do have problems with intake gaskets which are made out of plastic.They blow out and sucking in air causing a miss.Spray cab cleaner around the intake gasket area and if you notice a change,they are bad

[jharry]

Did you ever figure out what was causing it? I am currently having a very similar issue. The code will pop up at highway speeds and the truck shifts out of overdrive. after a few miles the light quits flashing and eventually it will shift back into overdrive.

[j cAT]

Originally Posted by jharry

Did you ever figure out what was causing it? I am currently having a very similar issue. The code will pop up at highway speeds and the truck shifts out of overdrive. after a few miles the light quits flashing and eventually it will shift back into overdrive.

welcome to the forum . when posting issues give all the details like what vehicle/engine/model year/mileage and any other work you or others have done to try and correct the issues at hand.

do not ask questions on old postings of others . the best way to get help faster is to start your own post with the info like I stated above.

as was mentioned to the member with a miss fire code of #7 cyl. this is most times a coolant/intake issue. you must check that you have the proper 50%min of GM approved coolant in the system. If you use the radiator to drain your system after flushing out the coolant system and then add pre mixed coolant you do not have the proper amount of coolant . If you drain the radiator then remove the drain plugs on the engine block you will find you need 4.5 gal of coolant to fill the system .
draining the radiator is about 1.75 GAL...
the metal with low amounts of coolant and the use of corrosive water eats at the metal then the gaskets blow out. If you are loosing coolant and see no leaks this is my guess whats going on.

[uspres2020]

That does not sound like the same as what was wrong with my truck. The problem on mine ended up being a piece of white debris in the fuel rail that I think might of been silicone, I had checked and cleared the fuel rails and the repair shop did numerous times, the last time I found it and took it out and it never had the problem again.

[j cAT]

Originally Posted by uspres2020

That does not sound like the same as what was wrong with my truck. The problem on mine ended up being a piece of white debris in the fuel rail that I think might of been silicone, I had checked and cleared the fuel rails and the repair shop did numerous times, the last time I found it and took it out and it never had the problem again.

white silicone in the fuel rail is odd since no silicone should be in there.

now white debris material in the fuel rail/filter/fuel tank would be contaminated gasoline with the 10% alcohol. filter should have caught it but if the fuel filter broke then you would get all sorts of problems more than a p0307 code. the white stuff is the growth of organic crap plugs everything up..