Alright so I had a misfire in my car 2 weeks after I got a new short block installed. Righ after the install everything was perfect and 2 weeks later got a misfire and check engine light. Had all 6 coils replaced and the code went away and it ran perfect. Now a week later the car is missing again randomly tho (ill start it and it will misfire, drive around and it clears, and comes back randomly, some times it's fine at start up but then driving it starts missing bad). I replaced all spark plugs and same issue.

The car hasn't thrown a code and not sure why. I checked all vacuum hoses and no leaks I can tell.

Any ideas what would cause the car to misfire randomly and not throw a code?

Did you end up finding out the problem?

Read the FSM

http://www.nicoclub.com/FSM/G35/Coupe/2003/ec.pdf


See Pages EC-290,291, 292,293,294

Diagnostic Procedure
ABS003CO
1.
CHECK FOR INTAKE AIR LEAK AND PCV HOSE
1. Start engine and run it at idle speed.
2. Listen for the sound of the intake air leak.
3. Check PCV hose connection.
OK or NG
OK >> GO TO 2.
NG >> Discover air leak location and repair.
2.
CHECK FOR EXHAUST SYSTEM CLOGGING
Stop engine and visually check exhaust tube, three way catalyst and muffler for dents.
OK or NG
OK >> GO TO 3.
NG >> Repair or replace it

Just replacing parts and guessing is not proper troubleshooting

Good luck

Telcoman

Telcoman

whats next after this? Been having this problem and I've checked vacuum system for leaks checking exhaust tomorrow

I'd check the evap solenoid and the small vacuum hose on the rear of the intake plenum.