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Merc 5.0l Lack of power no rpm over 3000rpm

greg hessler said:
THANKS!! This thing is killing me I've been doing this for a long time. I think soemwhere there is a bulletin that talks about the exhaust valves sucking up into the head I think that is what is wrong because it is leaking 20%m out the exhaust
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20 % lost is ok...
If you think it's exhaust, do this take exhaust bellows off at horns.... Run engine, you will get water and exhaust in boat...But this will till you if you have exhaust leak

Steve
 
mastertec Tech Mercury said:
On this sytem, is it DTS

Steve
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Hey
Just reaing this old post and I have exact same problem with Mercruiser 5.7EFI - tried new fuel direct from a can, new filter, fuel pressure 30 psi, replaced plugs cap & rotor, compression all circa 180 psi, checked and played around with ignition timing replaced ignition module (had a code 42 showing) checked exhaust flaps, hatches open, growth is not bad ------ it was ok last year although it has never reached wot in the 4 years I've had it - maybe get 4000 rpm before but now will not go over 3000 wont get up on plane just dog lazy and gutless... Did you ever resolve your problem ? or any other suggestions, only thing I havent tried is replace tacho which is a bit sticky but I'm scraping the barrel for things to try now.. Help:(
 
wmlaks said:
Have you checked to see if the timing chain has stretched? And have you run a vacuum test on the engine?
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Stretched Timing chain would rattle a bit and affect starting and run rough = I have none of this - in the marina it starts good revs good, even till it bounces on the limiter - at sea under load wont go past 3000 rpm - - Vacuum test on engine ? do you mean vac pipe from throttle body to fuel pump ? no excess pressure or vacuum when you remove the oil filler cap with motor running:confused:
 
Look on the back of the intake manifold rise next to the throttle body for a square drive plug...remove it and install a nipplle. Connect a vacuum guage to the nipple and read it. It can tell you a wealth of info about your engine.
 
I had a simular issuse on an enigine would start great idle great even rev up into the 5000 range. It just did not have any power under load. had no funny noises comeing from engine. The problem turned out to be a timing chain that had stretched.
 
I have exact same problem with my merc 5.0 1994.
there is 470 hours on it.
it was running fine till last year i took the engine out to do a rebuild on lower part pf engine including oil pan, timing chain cover , coupler and flywheel cover.
I put it in water today. In WOT the rpm goes up slowly and planes very slow.
when I back up on throttle to around 75% , I get the max RPM of 3500 out of it.
i checked wires, spark plugs and played with carburetor gas mixing adjuster.
nothing.
the engine vibrates which I haven’t had it last year.
Have you got to any solutions?
 
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