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Mercruiser 5.0 MPI Won't get Onto Plane after Top end Rebuild

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IM Buddy8

New member
Hello, this boat (2003 Sea Ray 240) ran fine this spring, until a pinhole rotted between the water jacket and the valve area in the head which made it hydrolock when we tried starting it after it sat for a few hours trickling in.


So we replaced head gaskets, heads (new remans with the same cast #), intake gaskets, exhaust manifolds, risers, exhaust flappers (the ones that stop water from coming in from a wake), intake gaskets, spark plugs, wires, cap, and a few other things while we were in there.


When we reassembled we followed the procedure fro pre-loading the lifters with one full turn after lash was removed. This felt like a lot, but it seems that Mercruiser manuals state this spec. Although on most small block chevy's I see 1/4,1/3, and 1/2 more commonly so I'm curious what others have done in their Mercruiser.


Set distributor to point at #1 cylinder with timing mark lined up with Cyl #1 at TDC. Started up well, idled well after a little bit of learning out from excess priming and runs excellent at idle and up to mid-speed. We thought we were all set, then took it out on the water (it's docked at a marina) and couldn't get it to more than 3100RPM's. Just two of us on it, it usually gets on plane in less than 10 seconds 90% of the time and it was calm with minimal wind, wave, current. Shut it down, checked oil level (good) tried loosening distributor and moving it as much as I could clockwise and counter-clockwise (it's the flat cap so it only turns a little bit in each direction) and it didn't seem to do anything. I have the 48 pin ECM-555 so I think if you're close to #1 at TDC that's all you need to do and the computer does the rest of the timing but correct me if I'm wrong.


Did a compression test, got between 165-175 in all cylinders so they are pretty well balanced with what I think is a respectable number.


No weird noises, normal oil pressure, doesn't overheat but lacking power. What could it be? The boat ran 100% strong this spring before the water leaked into the cylinder and stopped it from being able to start.


Any help would be greatly appreciated, located in Providence RI.


Thanks,
Ryan
 
Not sure but it’s a 2003 boat mercruiser 5.0 MPI with the 48pin ecm. Distributor cap is flat with plug wires coming out sides and the three pin plug on distributor doesn’t get plugged into anything.
 
o2batsea said:
The pic shows firing order as being 1-8-2-4-6-5-3-7, but the text says 1-8-4-3-5-6-7-2
Click to expand...
From my understanding with this cap when the rotor spins some of the positions don't align with the plug. Maybe internally it sends the signal to another plug port but it doesn't follow the firing order like a typical cap that has plug sockets on the top of it.
 
I went yesterday and did the following, still same issue won't go over 3100RPM.

Changed spark plugs (again...)
Triple checked firing order
Double checked fuel injector plugs to make sure they were on the right injectors
Replaced fuel/water filter (drained in to clear glass absolutely no water or debris in it, although it probably only had about 12 hours on it)
Put injector cleaner in the gas tank
Felt bottom for growth (almost none it's pretty clean/smooth)
Replaced PCV Valve
Changed oil and filter with OEM checked level to be sure we're right at the right level
Ran the following tests with spark arrestor off and boat "hood" up so air could get in there without issue

I also hooked up a fuel pressor gauge to the fuel rail. At idle it's nice and still at around 38PSI, when you get on it it doesn't dip lower than that and at WOT 3100RPM it is around 40-42 with a light flutter here and there but overall pretty stable and returns back to 38psi at idle without any drastic spikes or drops.

Then I hooked a vacuum gauge up to the intake manifold T'd it in. At idle it pulls vacuum down to around 13. If you rev it in neutral it will go up to around 5, then to around 22ish and then settle back down at around 13. With idling it up to maybe 1500RPM it will stay around 18-20. At WOT under load moving it will go to around 3 to 0 and then settle back down around 13 when you go to idle. It also is nice and static and stays at 13 when idling no fluttering and no slow drop or gain while idling.

I'm not sure if these results are good, I think maybe the rings are a little worn (motor has a decent amount of hours on it, the boat has 7XX and not sure if it's the original block but probably) and that's why I'm not getting 18-20inches at idle. Also not sure what the spec should be on fuel pressure, just know that if the numbers are good it was acting as it should.

I'm waiting on Rinda to send back my scanner that needed a new screen repair. The dash beeper beeps when I turn the key to on, so if that's the same alarm that would go off if it's in guardian mode for some reason then it's not sounding. Will report back with codes when I get scanner back but time is of the essence so I'm open to other ideas while waiting.

Thanks,
Ryan
 
Problem solved in case anyone else runs into this. I rescheduled valve lash and timing for the third time. Noticed prop had some barnacles on it but the boat itself was relatively clean. What do you know cleaning the props and outdrive with a scraper in the water and it planes as it should now. Can’t believe just 3 weeks of sitting causes so much growth that it couldn’t get on plane... can get 4250 rpms out of it now.

Thanks for your input and suggestions.
 
Probably not Mark. I'd bet the hull has some marine growth based on the OP's description. That'll effect performance.
 
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