Mercruiser 5.7 EFI Popping noise and lack of power

[rocklodger]

I have a 1997 Cobalt 190 with a merc 5.7l efi. After running about an hour or so I have errataic tach movement, hear a mettalic pop or backfire, and loose power over 2500 rpm's. The temp gage maintains 170 to 175 degrees. No alarm goes off. Boat has less than 300 hrs. Was told tach may be bad and disconnected wire and problem still exists. After letting sit for an hour or so can return to normal opperation. Any suggestions?

 

[Blk-n-Blu]

Re: Mercruiser 5.7 EFI Popping noise and lack of power

Have you checked the fuel filter / water seperator and tank vent.
here is a link to some basics:
http://www.sterndrives.com/engine_backfires.html

 

[rocklodger]

Re: Mercruiser 5.7 EFI Popping noise and lack of power

tank vent is ok, will check the fuel filter today.

 

[Blk-n-Blu]

Re: Mercruiser 5.7 EFI Popping noise and lack of power

Might also check the Anti-Syphon valve and tank pick-up line. Here:
http://www.sterndrives.com/anti-syphon-valve.html

 

[monterey98]

Re: Mercruiser 5.7 EFI Popping noise and lack of power

i have the same problem with my efi engine, i used a extra tank and still backfires on top speed, so my check valve is fine i can assume that, im checking everything else thinking that i can find and easy fix, dont want to think that i could have a major inside damage, like the one that requires a leak down test.

pls let me know if you found the solution man.