||02-15-2020 09:23 AM
I would be changing the plugs to at least OEM equivalent. These modern ignition systems are designed around very specific spark plugs, and they don't work well with low grade replacements. Many times its best to go directly to the dealer, just to make sure you get the correct ones to keep the system happy.
Every internal combustion engine needs three things to run well. Sufficient Fuel, sufficient spark to ignite that fuel, and sufficient Mechanical ability to draw in air and squeeze it down along with the fuel for proper burning and power production. Simply put- fuel, spark, compression. To diagnose misfires and check engine lights, these need to be kept in mind. Assuming the shop you used did a proper compression test, you can eliminate the Mechanical part of the equation. The engine must be able to draw in proper amounts of air through the air filter, intake and valvetrain, compress it mechanically, and expel it through the exhaust system. Eliminate this part of the trio. This leaves spark and fuel. You appear to have the improper spark plugs for your application, this means you more than likely have insufficient spark to ignite the air/fuel mixture. Replace spark plugs with OEM equivalent-just to get you on even ground to base your diagnostics from. You say you changed all the ignition coils, with the spark plugs correct? Assuming that the coils are all functioning correctly because they are new, double check the Human factor here, and make sure that ALL wiring connections are locked down and tight on the coils. If nothing obvious shows up, it's time to consider the last part of the trio. Fuel pump, fuel injectors, and fuel filter. Get a proper fuel Pressure gauge, and check the pressure for proper spec. Any discrepancy here would indicate fuel pump and fuel filter/regulator need replaced. If still having issues, remember, you have a individual fuel injector on every cylinder-just like the spark plugs and coils. You could have a couple of injectors that are not supplying proper fuel that would cause misfires as well. I had one injector on my WJ when i got it home that was setting a check engine light. It wasn't running poorly(no obvious miss) but the internal resistance in the injector itself was out of spec and causing the PCM to not be happy. I swapped the injector and all is well again. Eliminate your obvious spark plug problem by installing the correct plug for your application, then move on to the fuel system, and start eliminating items over there. Im betting you will find your problem then.