power loss misfire

mick

hi I run a 270 rinker 5. efi

 had an engine rebuild last year, engine runs sweet at dockside out side on the sea get to 3000 rpm wot. then back throttle off iac comes in pops and backfires and will not rev in or out of gear have to let it cool then limp back on tickover replaced map, iac, and thermo sensor ,scanned and no codes.cannot use in rough conditions for a fear of failure let it cool completely and it runs as if their is not a problem can use in marina in and out of gear fine no beeps no code faults.any ideas please regards .mike uk.

mick

well no replies on this problem

LaRea

Mike, how long do you need to let it cool before it goes back to normal?

I'm sure you've seen the fault code list, but if not, look here:

http://rinkerboats.vanillaforums.com/discussion/1042/encountering-faults-check-this-out

In some Merc engines, there are faults that will activate Engine Guardian (limp mode) but will NOT store a fault code.  For example, in my 496s, an overheat in the Exhaust Manifold Cooling Temp (EMCT) does not store a fault code.

I had an overheating problem caused by a blockage in the water intake, but it was hard to diagnose because there were no fault codes.

212rowboat

sounds to me like you have fuel delivery issues... change filters... check pressure while engine is under load... make sure vents are clear...

backfiring speaks of lean... it takes a lot more fuel to nail 3k rpm under load than not...  
 

F1100

Fuel... check first... if it was just rebuilt compression wont be an issue. Buy a inline external fuel pressure gauge if you dont have one, and watch to see what happens when it under load.

After that get your multimeter out and start testing the sensors for faults.

Its most likely something that was tweaked after the engine work.

F1100

also.. pull the plugs and have a look at them, to see if its an isolated piston(s) or the whole engine running like crap.. check gaps and color and smell.

F1100

also put a timing gun on the engine and see what its doing at load and various RPMs, perhaps the timing shifted when he did the work, and its out of wack

LaRea

How long do you need to let it cool before it comes back to normal?

You have probably already seen the faults list, but if not, look here:

http://rinkerboats.vanillaforums.com/discussion/1042/encountering-faults-check-this-out

In some engines, there are faults that will activate the Engine Guardian (limp mode) but do NOT record a fault code.  For example, if my 496 has an overheat in the Exhaust Manifold Cooling Temp (EMCT) circuit, it won't record a fault code.  

LaRea

How long do you need to let it cool before it comes back to normal?

You have probably already seen the faults list, but if not, look here:

http://rinkerboats.vanillaforums.com/discussion/1042/encountering-faults-check-this-out

In some engines, there are faults that will activate the Engine Guardian (limp mode) but do NOT record a fault code.  For example, if my 496 has an overheat in the Exhaust Manifold Cooling Temp (EMCT) circuit, it won't record a fault code.