I had a 1999 Volvo-Penta 5.0Gi vortec with TBI, not happy with the performance, decided to upgrade to a 5.7Gi. Bought a block and heads from Craiglist. Had a local machine shop rebuild c/w new pistons, camshaft etc..I put everything from the 5.0 onto the 5.7 ( ECM,TBI new ex-manifold, risers) I also put new filters,coil,dist'cap and rotor) plugs and wires were new last yr. I took it to a local marine shop to have the base timing set.The motor starts easy and idles smooth while on the driveway.
Took it out last Saturday for it's first sea trial. Idled out of harbor, throttled up to 2K and it backfired thru the carb. could'nt get past 2K without backfiring. Took a hour break and tried again. This time I accelerated very slowly and seemed OK at 2K. Slowly stepped up 200 RPM at a time.. OK to 3400 then backfired again. Seas were too rough to continue but want to try again this weekend. Any suggestions on what the backfiring problem could be? I have read numerous forums about changing the ECM. 50% say "Yes" it must be changed the other 50% say "no" its OK...confused!!!
Took it out last Saturday for it's first sea trial. Idled out of harbor, throttled up to 2K and it backfired thru the carb. could'nt get past 2K without backfiring. Took a hour break and tried again. This time I accelerated very slowly and seemed OK at 2K. Slowly stepped up 200 RPM at a time.. OK to 3400 then backfired again. Seas were too rough to continue but want to try again this weekend. Any suggestions on what the backfiring problem could be? I have read numerous forums about changing the ECM. 50% say "Yes" it must be changed the other 50% say "no" its OK...confused!!!