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6.0L idles fine but runs rough under load.

C

C_Malin

New member
Had a customer drop this boat off because he ran it aground and ripped the rutter out of the hull. pulled the engine to have the fiberglass repaired. Installed the engine and it runs like crap. Idle and throttle only it runs fine but under a load its detinating. Power balanced the engine and it passed, fuel pressure test passed, Spark plugs are bright white which would lead me to a fuel problem. Any ideas?

Thanks
Chad
 
Temporarily use a 6 gallon outboard motor tank filled with fresh fuel as the fuel source. This will confirm if the existing fuel or fuel system needs attention or not
 
I' ve run it with a different fuel tank with good fuel with the same result. Its not pulling any codes and I've changed the cam and crank sensors. I've done a node test and all injectors are getting power. I've swapped the fuel pump and still have the problem. I've also pulled the engine again and checked the timing which is dead on. The oil has only about an hour on it but its very black. Any ideas?
 
Also this is a 6.0l marinepower engine and the timing is done by the ecm. it just seems to fall on its face under a load and starts missing and it sounds like the valves are clattering
 
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I'd say with no codes, the issue is due to something beyond the computer's control. Power balance via the computer isn't always foolproof. Fuel pressure test done at idle or under load and at cruise & WOT? Idle only won't show issues in the fuel delivery side. A vacuum gauge on the suction side (use the spare IN fitting on the filter) can show its condition. Last checks would be vacuum gauge...if it shows an issue, could be a mechanical issue with the engine - I'd get the leakdown tester out.
 
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