500rpm low at WOT 5.7 merc black scorpion

[monkstr6100]

I have a 2006 Gekko GTR with a merc black scorpion 330hp. My issue is that at WOT I only run 4700rpm or so. Checked by tach and perfect pass. Speed tops at 43-44. Checked by gauge, perfect pass, and GPS. This has run like this since I owned it almost two years ago. What I have done so far. Replaced plugs, cap, rotor, wires, fuel filters (water separator and inline), vac tested fuel feed line, compression tested all 8 (160-165psi), did fuel pressure test (26PSI at idle to about 2300rpms), vac tested engine with no fluctuations on the gauge but forgot the reading, the map sensor vac hose was barely on the tip of map sensor nipple so I fully pushed that on with no change. I am sure I have done more but forgot. No starting, dying, stalling, or anything like that issues. Can smell gas when I am skiing and down wind of the boat. Also set the linkage so I am for sure getting wide open on throttle body. Any help would be awesome. Thanks in advance, Zach J

 

[monkstr6100]

Also have installed brand new acme prop, the correct one, and did a drive shaft alignment. Ran temporary clear fuel line and had no air bubbles in feed line. With just me in the boat I can get 4800RPM, but add another person and it drops to 4700, so there's is a lack of power. No warning horns for codes either.

 

[alldodge]

I have a 2006 Gekko GTR with a merc black scorpion 330hp. My issue is that at WOT I only run 4700rpm or so. Checked by tach and perfect pass. Speed tops at 43-44. Checked by gauge, perfect pass, and GPS. This has run like this since I owned it almost two years ago. What I have done so far. Replaced plugs, cap, rotor, wires, fuel filters (water separator and inline), vac tested fuel feed line, compression tested all 8 (160-165psi), did fuel pressure test (26PSI at idle to about 2300rpms), vac tested engine with no fluctuations on the gauge but forgot the reading, the map sensor vac hose was barely on the tip of map sensor nipple so I fully pushed that on with no change. I am sure I have done more but forgot. No starting, dying, stalling, or anything like that issues. Can smell gas when I am skiing and down wind of the boat. Also set the linkage so I am for sure getting wide open on throttle body. Any help would be awesome. Thanks in advance, Zach J

Fuel pressure is to low, manual states should be 43 psi at 1800 rpm. What do your plugs look like?

and :welcome: to iboats

 

[NHGuy]

Have you had it scanned? Does it show a trouble code?
26 psi sounds low for fuel pressure, cars are too low at 40. Is any fuel leaking? Perhaps under the top cover near the fuel rail or parts of the pressurized fuel distribution system?

 

[monkstr6100]

I thought 43 psi at first as well. Just like all other merc MPI, but the black scorpion is 30PSI. Even says it on the "cool fuel" high pressure pump hold down. Didn't notice that till I did tons of tests trying to get 43PSI and even replaced the high pressure pump.

 

[monkstr6100]

30PSI verified by the merc mechanic when I emailed mercury. They even sent me the fuel pressure section out of the service manual that lists it.

 

[Fastatv]

I have a 2006 Gekko GTR with a merc black scorpion 330hp. My issue is that at WOT I only run 4700rpm or so. Checked by tach and perfect pass. Speed tops at 43-44. Checked by gauge, perfect pass, and GPS. This has run like this since I owned it almost two years ago. What I have done so far. Replaced plugs, cap, rotor, wires, fuel filters (water separator and inline), vac tested fuel feed line, compression tested all 8 (160-165psi), did fuel pressure test (26PSI at idle to about 2300rpms), vac tested engine with no fluctuations on the gauge but forgot the reading, the map sensor vac hose was barely on the tip of map sensor nipple so I fully pushed that on with no change. I am sure I have done more but forgot. No starting, dying, stalling, or anything like that issues. Can smell gas when I am skiing and down wind of the boat. Also set the linkage so I am for sure getting wide open on throttle body. Any help would be awesome. Thanks in advance, Zach J

I believe the WOT rpm for this engine can be up to 5200. Its ran this way since you have owned it right? .....dumb question here....are you 100% sure its propped correctly....prop not too high in pitch? Have you checked the base timing and timing advance?

 

[Bondo]

I have a 2006 Gekko GTR with a merc black scorpion 330hp. My issue is that at WOT I only run 4700rpm or so. Checked by tach and perfect pass. Speed tops at 43-44. Checked by gauge, perfect pass, and GPS. This has run like this since I owned it almost two years ago. What I have done so far. Replaced plugs, cap, rotor, wires, fuel filters (water separator and inline), vac tested fuel feed line, compression tested all 8 (160-165psi), did fuel pressure test (26PSI at idle to about 2300rpms), vac tested engine with no fluctuations on the gauge but forgot the reading, the map sensor vac hose was barely on the tip of map sensor nipple so I fully pushed that on with no change. I am sure I have done more but forgot. No starting, dying, stalling, or anything like that issues. Can smell gas when I am skiing and down wind of the boat. Also set the linkage so I am for sure getting wide open on throttle body. Any help would be awesome. Thanks in advance, Zach J

Ayuh,..... Welcome Aboard,..... So what's the problem,..??

4700 rpms at Wot is well within' the expected window of operation,........

 

[monkstr6100]

Have not checked the base or advance timing. I think I need to hook it up to the diacom program for that correct? When I was testing my MAP sensor voltage today I noticed that there were shiny stainless bolts holding the IAC on and that there are two gaskets stacked at the base of the IAC? With some white corrosion around it as well? Will do some looking but I assume it does not take two gaskets there. Yeah the prop is for sure right. Talked to the owner of gekko before I ordered the prop. Had a .625 higher pitch on it before and switching to this lower pitch made about zero difference.

 

[alldodge]

What do your plugs look like?

 

[monkstr6100]

I would be fine with the 4700, but I have talked to other guys with the exact same boat/engine/prop setup at are running 5200rpm and 50mph! Can the engine be restricted by the ECM, this was a Demo boat so maybe they put something in there to keep the revs down? Need my buddy to hook it up to his merc computer again but while running it on the water this time. Showed no codes and 100% power available when running on the "fake a lake" in the driveway a few weeks ago. Pulled the plugs a week ago to do compression test and they all looked the same and good. None were wet. Light white if I remember correct. Pulled one plug wire at a time while at idle and every one made the same drop in RPM. Thanks and keep the ideas coming. I wish I never knew there was something possibly wrong with my boat! Ha!

 

[monkstr6100]

When my buddy the merc mechanic hooked up a timing light to it the timing really wandered a TON! Would go from the bottom of the scale to the top of the scale. Slowly swing back and forth? Full retard then full advance. At idle and at like 2000rpm. Is this normal? This was without the DIACOM hooked up though. I am sorry for all the long winded text but I figure the more info the better.

 

[thumpar]

How much does the boat weight?

 

[monkstr6100]

Around 2300 empty.

 

[thumpar]

Have looked to see if the previous owner might have added weight for ballist? The guy I bought my boat from also has a Supra that he added concrete to make a better wake.

 

[monkstr6100]

@thumpar no def no extra weight added. It's a ski boat only. The guy I got it from was a course skier only, so weight is the devil to those guys, but good idea just the same. I just sent an email off to him as well to see if it ever ran more rpm than what it is now. I can see that there is also a replaced right side exhaust manifold gasket, so some work has been done on it at some point. Maybe wrong gasket and there is an exhaust restriction? Is that crazy?

 

[monkstr6100]

Also, there is oil on the right valve cover, the one with the PCV and oil fill. PCV seems to work, but maybe it's not working well and causing the extra pressure to cause the leaks around the fill tube and PCV boot?

 

[alldodge]

When my buddy the merc mechanic hooked up a timing light to it the timing really wandered a TON! Would go from the bottom of the scale to the top of the scale. Slowly swing back and forth? Full retard then full advance. At idle and at like 2000rpm. Is this normal? This was without the DIACOM hooked up though. I am sorry for all the long winded text but I figure the more info the better.

No, wondering timing is not normal

Did you put the engine in base timing mode during your look see?

 

[monkstr6100]

No it was not in base timing. Can I put it in base timing without a diacom program? Serial number 0W399769.

 

[Fun Times]

No it was not in base timing. Can I put it in base timing without a diacom program? Serial number 0W399769.

Your engine "timing" by way of a timing light is non adjustable on this engine model. But the mechanical settings/workings of the distributor components still has to be within the correct range so the proper plugs will get spark at the right time. So if it wasn't/hasn't ever been turned, no need to do it now. Be sure to read the timing parameters on the scan tool.

I noticed that there were shiny stainless bolts holding the IAC on and that there are two gaskets stacked at the base of the IAC? With some white corrosion around it as well? Will do some looking but I assume it does not take two gaskets there.]

Should be one gasket. http://www.mercruiserparts.com/Show...8&bnbr=80&bdesc=Intake+Manifold+And+Fuel+Rail

Here's your parts catalog if needed. http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=835003003