You are very welcome.
If it is a specific cylinder causing the misfire, it should show up by scanning the computer. You may not need all coils.
Next, a backfire is often caused by a lean fuel mixture. Take a look through this link:
It could be the result of a vacuum leak.
Let me know if you pulled diagnostic trouble codes that may point us in a specific direction. Also, let me know if by chance you have a live data scanner. If you do, please let me know what both the short and long term fuel trims are.
Also, here are the directions for replacing the intake gasket. The torque specs and sequence are included. The attached pictures correlate with the directions.
2004 Infiniti G35 Sedan V6-3.5L (VQ35DE)
Vehicle Engine, Cooling and Exhaust Engine Intake Manifold Service and Repair Procedures Intake Manifold
1. Release fuel pressure.
2. Remove intake manifold collector (upper) and (lower).
3. Remove fuel tube and fuel injector assembly.
4. Loosen bolts and nuts in reverse order of illustration to remove intake manifold assembly with power tool.
INSPECTION AFTER REMOVAL
Using straightedge and feeler gauge, inspect the surface distortion of each surface on intake manifold.
Limit: .................... 0.1 mm (0.04 inch)
Install in the reverse order of removal paying attention to the following.
Installation of Intake Manifold
If stud bolts were removed, install them and tighten to the torque specified below.
9.8 - 11.8 Nm (1.0 - 1.2 kgf-cm, 7.3 - 8.7 ft. lbs.)
Tighten all mounting bolts and nuts to specified torque in three or more steps in numerical order shown in figure.
R 1st step: .................... 4.9 - 9.8 Nm (0.5 -1.0 kgf-cm, 4 - 7 ft. lbs.)
R 2nd step: .................... 26.5 - 31.4 (2.7 - 3.2 kgf-cm, 20 - 23 ft. lbs.)
R 3rd step and after: .................... 26.5 - 31.4 (2.7 - 3.2 kgf-cm, 20 - 23 ft. lbs.)
I will watch for your reply.
Images (Click to enlarge)
Sunday, January 26th, 2020 AT 5:53 PM