I need some help with my 5.0L 260hp engine (GM 305ci). Engine starts and idles fine. On acceleration, it misses terribly. Doesn't matter how aggressively I accelerate. I can hear the engine backfire through the throttle body like the timing is off. Does it cold and does it warmed up.
If I get the boat on plane and cruise at 35mph or so for about 30 minutes, it runs fine. Accelerate at any rate and no miss. Strange!
What I've done so far:
1) New fuel pump and IAC module replaced last year. Codes cleared.
2) Pulled engine codes after poor performance. No codes stored.
3) Replaced Throttle Postion Sensor. No change.
4) Ran 50 gallons of fuel with injector cleaner. No change.
I'm grasping at straws now. Some think it's a crank sensor. Others think ignition so I could replace the dist cap, rotor and spark plugs in search of something being cracked. I could pull the injectors for testing and cleaning. The list goes on but it's all guessing at this point.
Suggestions?
If I get the boat on plane and cruise at 35mph or so for about 30 minutes, it runs fine. Accelerate at any rate and no miss. Strange!
What I've done so far:
1) New fuel pump and IAC module replaced last year. Codes cleared.
2) Pulled engine codes after poor performance. No codes stored.
3) Replaced Throttle Postion Sensor. No change.
4) Ran 50 gallons of fuel with injector cleaner. No change.
I'm grasping at straws now. Some think it's a crank sensor. Others think ignition so I could replace the dist cap, rotor and spark plugs in search of something being cracked. I could pull the injectors for testing and cleaning. The list goes on but it's all guessing at this point.
Suggestions?
