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Merc 5.0l Lack of power no rpm over 3000rpm

G

greg hessler

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I have a 2002 5.0l mcm Serial #OM336918 471 hours Maintenance kept to the letter. It will not run over 3000rpm We have done the following. Compression test Good Fuel pressure test good Scanned with diacom no codes all parameters in the game new plugs cap and rotor Replaced the exhaust water shutters Cleaned all debris from exhaust. Gas tank vent clean as well as anti siphon valve Fresh gas no Prop or drive changes I have not leak tested the engine yet but that is next.
I think somewhere, there may be a merc sercvice bulletin about the exhaust valves sucking up into the heads cannot find it
We changed a few things to just be SURE both fuel pumps and regulator and the map sensor
It still will not run over 3000rpm
HELP
 
List of possible causes of low WOT

List of possible causes of low WOT (Wide Open Throttle) rpm.

In no particular order

Engine Won't Reach Operating RPM. Check

1. Fuel condition. Type and Octane possibly old fuel
2. Propeller pitch or diameter, damaged blades
3. Restricted fuel pickup tube or anti siphon valve Fuel System Test
4. Crankcase oil volume, high oil level can cause aerated oil and lifter collapse
5. Marine growth on hull and outdrive
6. Wrong gear ratio in outdrive
7. Restricted carburetor air intake (clogged flame arrestor)
8. Restricted exhaust system (broken exhaust shutters/flappers) in engine transom shield or drive
9. Poor cylinder compression Compression Test
10. Carburetor defective, or wrong type.
11. Fuel pump pressure and vacuum
12. Boat overloaded, improperly loaded, or improperly trimmed.
13. Engine Overheating
14. Engine timing and ignition system operation
15. Remote control cables and linkage for proper travel to open throttle plates fully.

Above copied nd pasted from another website Don s is the author.


​
 
I have maintained the boat since it was new It belongs to s customer of mine. I have all the merc diag equipment and have performed all the tests listed in the reply you pasted
We summerized the boat drove it to the slip Customer shows up drve it for 2 hours then no power. We found the exhaust clogged with broken shutter valves performed all lknown tests
Maybe the injector driver is bad it is a 555 ecm wot 100% fuel pressure good tried map sensor new plugs cap and rotor timing compression test good going to leak the cylinders
 
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
 
The reason for opening the hatch while running comes from a recent issue similar to yours. It turned out to be an exhaust leak into engine compartment. Would run no problem with hatch open. Replaced manifold gasket and solved the issue. Worth a try.
 
Wonder if Guardian is kicking in for some reason? It would reduce available power to certain percentage based on a problem the computer is detecting. Does the engine horn (alarm) ever come on (beep)? Would be good to see if you have full power available when trying to go over 3000 rpm. Need to read while running.
 
Change the distributor cap and rotor. This will cause loss of RPM.

Make sure the installed spark plugs are correct. MR43LTS(Vortec) not MR43TS(Non Vortec). The MR43TS will fit and give you a power loss.
 
you went down the list one by one and checking off each and every item ?

If you did then the motor is running correctly.

you say you got all the pieces ? Maybe not. Maybe the exhaust is still clogged.

You missed something or the motor would be running good.
 
Yes 29" @idle goes away with throttle increase settles around 19" but when the engine is hot the needle starts to go crazy I think the heads gaskets may be leaking or the heads are cracked into the exhaust.
 
We are going to get into it monday I have all of the water shutter valve pieces. It is driving me crazy
COmpression is good but when we leak it I can hear air coming out the exhaust and the engine vacuum goes crazy @ 1500rpm
 
No mis fire. We got it ready for the season ran great sat for a few weeks delivered it to the customer ran great to the dock. Customer showed up next day would not run. Throttle blades open full just feels like exhaust clogged the vacuum test I took I'm not sure I like it 29" at idle 15"-20" at 1500rpm needle bouncing a lot going to pull intake today
 
Greg, Ditto Woodie's suggestions.

Also look at Chief's list item #14 in post # 3.
If all else is A-OK, ignition TAT (total advance timing) may be the culprit.
No gasoline Marine Engine will achieve WOT RPM if the TAT spec is not being met!
Possible reason for this NOT being met, could be a faulty module.

You'll need to mark off your harmonic balancer, and and strobe the timing marks as to check the progressive advance!
Plot this out on paper in graph form.
Then compare to the OEM advance curve.
Perhaps post the results on the forum here.

Does this engine ignition system incorporate a rev limiter?

.
 
Last edited:
Greg, any TA number must be associated with an RPM.
Without an RPM, the number is pretty much meaningless..... and is risky!

So.... while I'm thinking that a FULL-IN 24* TA is on the the light side......., need to know at which RPM this is FULL-IN!

.
 
you posted compression is good then you ask about a bulletin about a valve getting sucked up.

What was the compression numbers.

Maybe your client sucked up sand and the riser is full of sand or the block.

Yea i seen that also the block completely full of sand all the way to the risers.
 
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