6.2 trouble shooting help
 

Hey guys, hoping someone out there might have some insight on my engine troubles. Merc 6.2 2008 model. Engine idles a bit rough and will stall, however, also does restart. Main trouble starts at around 2000 RPM, when the engine starts to "chop", from 2000 RPM to around 500 RPM. The boat has twins, so I can get the boat on plane by running the good engine harder, which would take some load off the bad engine- but the bad engine still won't go over 2000 RPM. Seems electrical, but have swapped just about everything from the good engine, with the same results. Any ideas welcome!

How old was the fuel sitting in the new style gen 3 cool fuel tank? You have too fuel pumps in that tank mounted on the engine one of the pumps could be going bad, Or you have too fuel filters inside that same tank that will get dirty. you should check your fuel pressure to start with. See # 21 & 26. http://www.mercruiserparts.com/Show_...ule%28Bravo%29 Also you will need something like this to check fuel pressure http://www.harborfreight.com/cpi/cta...emnumber=92699. http://www.harborfreight.com/cpi/cta...CategoryID=455

The fuel for both engines is from one tank and never sits to long. I just went out and cleaned then swapped the two cool fuel filters- port/star engines.

The reason I don't think it's fuel related is that it's not "load" dependant. when planning, if both throttles are at the same point- the star engine starts chopping rpms at just before 2000. Now if I advance the port throttle- to plane the boat( to around 4000), then play with the starboard throttle, it stays the same- chops just before 2000. If it was fuel wouldn't the rpms go up on the starboard engine as there would be less load- being that the boat was now on a plane( port engine at 4000)? Does that make sence?

Also, I've got Diacom software, and no code show up.

It is possible you have a problem with the fuel pick-up in the gas tank for that engine.

Last year I noticed when below 1/2 tank and getting on plane my starboard engine would start to cut-out. It ended up that the dip tube on the pick-up came loose and was allowing air to get sucked up into the fuel pump. This caused it to lose its prime and the engine would stumble. It would first show up when getting on plane, like 2000 rpm...

does the stumble go away after getting on plane and running ? I had a float sticking on one of my carbs... loaded up the cylinder then it finally burned all the excess fuel away after 5 mins. my thought,

No, won't get past it.

Did you swap the fuel pumps? New fuel/water separators and inline fuel filters?

I had similar issues a few years ago. Twin 496HOs, but both had same symptoms. No codes in ECU. Ethanol fuel had ruined all that i mentioned above on both engines.

I understand what you are saying, But both engines need to be 100% One engine will not help get the other one going in most cases, You can never rule out the fuel system untill you know for sure it is working right. And the problem with your fuel system is you can test the hi fuel pump up on top of the engine, On the fuel rail, But the hard one to test is the low pressure fuel pump, Because there is no valve to hook your fuel gauge up to. You might need to either rig something up or could go old school and try a vacuum gauge on it, Or trust your eye sight and get a strong clear hose hook it to the fuel inlet hose barb on the side of the fuel PUMP tank mounted to the engine and get a smaller fuel tank and stick the hose in there and have some one key it up a few times and then start the engine and try to see if you are getting a good strong flow with no air bubbels in the line and see if the enging run better now. Do you have one tank running both engines or do you have too tanks? Once you know the fuel is good then you would start looking at the power side of things. Unless you see something not with in range with the Diacom software hooked up in real time then you would go after that.

Austin, let us know what you find out. I am curious.

Did a compression test and Cyl #6 had 0, #4 was 135. Pulled the valve cover to find #6 stuck open. Pulled the ehuast manifold to look inside with a flashlight- #6 was of couse open and #4 didn't appear to be seating very well. With a piece of wood and a hammer I tapped the valve on #6 and it did come back up. Ran a couple of compression test and got different readings between 135-150. Took the head off and brought it to a local machine shop. I am waiting to hear something next week, but, hopefully the propblems found. I read an article on burnt sticking valves and it sounds about right.

There was a bent valve on #6 exhaust, so that was replaced and they re cut valve seats on all. When reinstalling the head there was a small mark on the top of piston #6 where the valve touched- didn't look bad.

When adjusting the valves I am following the Merc manual which tells me to bring it to TDC on #1 and set certain intake/exhaust valves. Then rotate 360 and then set the remaining valves- so two positions on the crank set all of the valves. With the crank at position 2 ( 360 from TDC #1) it should be TDC #6 , but when I adjust this valve the exhaust valve creaks slightly open... is this the sign of something off? I hear of posts where people question the timing chain... is the crank and cam being "off" the Hallmark of this?

Sorry to hear of your problems.

This is the easiest way I have found to adjust valves:

When adjusting the exhaust valves watch the intake valve for that cylinder while rotating the crankshaft. When the intake valve is closing about mid stroke (intake valve going up) the exhaust valve is fully closed and can be adjusted.

When adjusting the intake valve watch the corresponding exhaust valve while rotating the crankshaft. When the exhaust valve is opening (exhaust valve going down) you can adjust the intake valve.

I just remember 'intake up' and 'exhaust down'.

4mula,

Ran it this morning with the valve cover off and noticed that only a few of the push rods had oil coming up. It was idling poorly, but I ran it for around ten minutes , but the majority of the push rods still had no oil coming up. If I understand correctly there should be a little "pop" of oil coming up from the top of each push rod and running on the top of the rocker. I took the intake manifold off and took the lifters out. I took one apart and found some bits of metal - but not much. The oil in the lifter looked old- like it wasn't cycling oil through it. Dose any one out there know if the lifter should be "pumping" oil?? When putting it back together( the lifter) should it be filled with oil or left dry?

Any good Mercrusier mechanic want a free vacation to the Bahamas??? I'm serious.

4mula,

That sounds like a good way- it makes sence anyway. So basically adjust each one when it's fully closed.