Car misfires and error code P0306 and P0303 is shown?

This codes are indication on car misfire.
As per code P0306 and P0303 this is indication that cylinder number 3 and 6 are misfiring and needs inspection.

Basically the problem in this cases are
Faulty fuel pump, fuel filter, spark plugs, coils on #3 and 6, Intake upper and lower gaskets.

There are four things that could cause a missfire on two cylinders on seperate banks of the engine .
1.) Spark plug
2.) Coil
3.) Fuel injector
4. ) And mechanical, like bent valve , worn rings etc etc.

If you have already replaced the plugs and coils , so that leaves only injectors,, a injector will mess up some times, like if its clogged , on heavy loads not enough gas will be sent out ,, and a mechanical problem will happen all the time. So it looks like you may have two bad injectors,if you are sure that spark plugs and coils are ok or already replaced.

If injectors are bad you will also notice some kind of oil burning smell.

Lets say your rings on the piston was bad , leaking ,, under a heavy load it could cause a miss, and then you would get that smell.

But how many miles on this truck,if over 100k.Then you may want to do a compression test on those cylinders,before you replace the injectors,you can rent one at any auto parts store,do a compression test on all of them so you can compare the readings to the others that do not have a problem.

This will give you better confirmation of the problem.

Basically injectors are Approx $70 to $75 each for replacement.

This details will help.

Thanks.

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