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backfire101

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"I have a 2005 5.0 Volvo Penta

"I have a 2005 5.0 Volvo Penta OSi-E, with 130 hours on it. Had standard 100 service done at 90 hours. After 1 or 2 hours of running at 4000 rpm (25 mph) the engine begins backfiring (pop, pop, pop). It loses about 200-300 rpm immediately before the backfire and then returns to normal operation after the backfire for about 15 seconds - then it happens again. The problem never happens at idle/no wake speeds (i.e. it can be backfiring, but if I bring if off plane it runs fine). The next morning the boat runs fine for 1-2 hours and the whole thing repeats again. I have replaced the fuel/water separators twice and had the tank checked for water/debris by a pro - no water in the fuel. I took it in to my mechanic and the engine returned no error codes. Any thoughts?"
 
"I would guess You have a valv

"I would guess You have a valve/lifter issue.
Try to locate which cylinder, the sparks should give an indication.
Then turn the engine manually until that cyl is at TDC, loosen the adjustment nut for the rockerarms and measure that the valve stems have the same hight! If the inntake valve is higher,You probably have a 'mushroom' valve which must be replaced. Sometimes this may even appear on a comp test, nut not allways."
 
"I recently ingested some sand

"I recently ingested some sand after having the service done impellor, fogging oil, thermostat on occasion when you idle around (less than 1,000RPM)for approx 10 - 15 minutes any application of the throttle causes a power loss. Place in Neutral and then in forward and same thing. Then in Neutral the engine RPM increases to between 1500 and 2200 RPM and the issue is gone. Help!!"
 
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