6.2 rough idle, not running right

[lucky7's]

Have a 2002 mercruiser 6.2 mpi. Ran all day fine, on the way back to the boat ramp experienced a lack of power. Pulled out spark plugs and cylinder 1 and 3 the electrodes were melted. Put new plugs in it, checked and cleaned distributor cap, rotor, iac, and took it out for a test run. Seemed to run better, had plenty of power for hole shot. After it warmed up it would barley idle. Seemed to be misfiring and on the same side that the plugs were melted on. Also at wot the engine would make a little popping noise but still had power.. So I went home and pulled plugs out and they all looked like they were burning fine.. Really stumped.. Help anyone?

 

[boatguya1]

Re: 6.2 rough idle, not running right

First thing compression test. Then I'd check the fuel pressure at the rail when problem is occuring. Could also be a vacume leak when things get up to temp. A temp sensor shouldn't throw things out far enough to melt plugs down so I don't think it's that. Also make sure you don't have water in your fuel.

James

 

[Zackman]

Re: 6.2 rough idle, not running right

Would agree with most of what James listed, except the vacuum leak (no vacuum taps/connections on the mpi engine).​

Here is the check list from the manual...​

 

[boatguya1]

Re: 6.2 rough idle, not running right

Yea I guess that was poorly worded. I meant a leak where the intake or something Is letting in air where it shouldn't after warming up causeing a lean condition.

Just to be a stickler isn't there a vacume line to the fuel pressure regulator? I'm not looking at a drawing so I could be wrong. Not that this was what I was thinking.

James

 

[boatguya1]

Re: 6.2 rough idle, not running right

If all else looks good an injector balance test to make sure the injectors on the two cylinders that ate the spark plugs are flowing ok. Also hook up a scan tool and see what the computer is seeing from the sensors.

James

 

[Bondo]

Re: 6.2 rough idle, not running right

Ok guys got it fixed!! The distributor cap and rotor was corroded up. Pulled it apart and cleaned all the electrodes with some fine sandpaper and put it back together and no more misfire.. Saved myself 50 bucks instead of buying a new one.

Think i figured it out. the IAC "idle air control valve does not work.. I pulled it out and the thing is like stuck barely open. I pulled it off and left the wires hooked up to it and it does not move at all. Its supposed to close when you give it throttle and its supposed to be open at idle. Also I have replace three of these things and I know it is supposed to be shut totally when there is no power going to it. I pulled it off and its like half way open. I ran the engine with it hooked up to see if it closed and it did not.... Sooo????

Well I know it gets wet back there when I have alot of people swimming in out of the back of the boat. When they get in and out the water drips through the engine cover lid between the lid and the transom. There is a gutter back there but it does not work very well. The distributor is right under there. Its also claimed my trim pump bracket.. I run in brackish water half of the time so its to be expected. But all in all Ive kept the corrosion down to a minimum.

Ayuh,.... You've got 3 or 4 threads about this Same Issue,....
In 1 of your Other threads,... I mentioned you have to dry out your motor room...

My WAGuess is,...
You've got All kinds of Problems,...
All related to the Saltwater baths you keep giving your motor....

 

[boatguya1]

Re: 6.2 rough idle, not running right

Ayuh,.... You've got 3 or 4 threads about this Same Issue,....
In 1 of your Other threads,... I mentioned you have to dry out your motor room...

My WAGuess is,...
You've got All kinds of Problems,...
All related to the Saltwater baths you keep giving your motor....

James

 

[lucky7's]

Re: 6.2 rough idle, not running right

Well yea sorry for the other threads.. I though the problem was resolved because the problem seemed intermittent.. well Ive about narrowed it down. All of the cylinders on the right bank seem to be running to hot. The plugs are a little glazed. All of the cylinders on the left bank are burning ok. The miss firing is occuring on the right bank where the I know they are running to got (glazed new plugs and melted 2 old ones) So maybe not enough fuel? Also the fuel rail on that side is the furthest away from the fuel supply. But i think im narrowing it down. For some reason the cylinders on the right bank are running too hot.. Thanks for any help guys...

 

[Fun Times]

Re: 6.2 rough idle, not running right

Have a 2002 mercruiser 6.2 mpi. Ran all day fine, on the way back to the boat ramp experienced a lack of power. Pulled out spark plugs and cylinder 1 and 3 the electrodes were melted. Put new plugs in it, checked and cleaned distributor cap, rotor, iac, and took it out for a test run. Seemed to run better, had plenty of power for hole shot. After it warmed up it would barley idle. Seemed to be misfiring and on the same side that the plugs were melted on. Also at wot the engine would make a little popping noise but still had power.. So I went home and pulled plugs out and they all looked like they were burning fine.. Really stumped.. Help anyone?

Hi I was doing some reading to day and found some one talking about the same thing you are talking about and thought I would just pass the link on for you to read to help you out a little. It seems like the spark plugs that cost $18.00 and that should be lasting to 300 hours might either be a cheap quality spark plug made at certin times, And over time some of them are burning up or geting eaten up for no reason, Or they had a few bad batches made up at some point in time would be my guess but I do not really no. Now the 496 plug is not the same part number as the 6.2 But they are close to each other and should be a sister type plug. But at the same time from what I remember I was told while at service schools is you should not run ANY after market spark plugs at all or you will have big problems. So that being said you still should only run the AC delco type plug only, Just put a new set in and run it. But if you can keep a eye on them over short periods of time to be safe till you get to know your engine. I believe you will find the last few post interesting. Hope this helps a little, Good luck.http://www.performanceboats.com/html/forums/showthread.php?t=37580

 

[lucky7's]

Re: 6.2 rough idle, not running right

The problem was the intake manifold gasket on that side failed and was leaking air and water into two of the cylinders and burned up the intake valves.