engine misses

[c03camson]

trying to figure out why the engine keeps missing. Does it at idle and when taking off. Once up on plane sometimes it will do it and sometimes it wont. Changed the water/fuel separator and run stabil in the tank.

Im going to check the spark plugs next just wondering what else I can check while im in there. Also is there a code reader or anything I could hook up to see if somethings wrong? Thanks

2003 5.0 mpi merc

 

[Aloysius]

Re: engine misses

Does your distributor have a flat top, with the plug wires on the side?

 

[Don S]

Re: engine misses

When was the last FULL tune up?

Not only tune up, but fuel filters and other preventive maintenance checks (drive, alignment, impellers etc). With a 7 year old engine you should have at least changed the plugs, cap and rotor, impeller, bellows and a few other things, at least once and hopefully you did a compression test at some point to keep track of how your engine is doing.

 

[c03camson]

Re: engine misses

I bought the boat about 9 months ago and have only changed the oil and filter, fuel/separator. Boat ran awesome all summer for the most part but now this problem. Im not sure what has been done prior to me owning it. I plan on winterizing it and pulling the outdrive to check gimbal bearing, bellows, u joints and alignment. So I need to replace all the ignition system components too?

 

[Don S]

Re: engine misses

So I need to replace all the ignition system components too?

Yeah, it's all probably 7 years old.

 

[Aloysius]

Re: engine misses

If your engine has the flat top distributor cap, they are notorious for being defective out of the box..they short out internally. Same with the rotors. Excessive (stock) plug gap can make the problem worse.

 

[c03camson]

Re: engine misses

It is the flat one with the plugs coming out the side. How do I check to see if those components are faulty or should I just replace it all? Cap, rotor, plugs and wires?

 

[dubs283]

Re: engine misses

replace it all

when you pull the cap, notice how much buildup is on the contact posts

when i see it, i'm amazed that they still run

 

[Aloysius]

Re: engine misses

The distributor MUST be phased properly..turning the distributor does NOT affect timing.

The rotor MUSt be matched to the cap. I've seen rotors with over 1/8th inch gap between the rotor and the cap terminal.

Reduce the plug gap to 0.035".

 

[c03camson]

Re: engine misses

So I pulled each plug wire off of the plug one by one while the engine was running and I didn't notice any difference in how the engine ran. Does that mean the plugs are good? Im confused.

 

[dubs283]

Re: engine misses

the ecm will keep the engine running as close to best it can

pulling the plug wires won't give you a great indication as to wether or not you have a problem with a cylinder

have you done the full tune up recommended in earlier posts??

 

[c03camson]

Re: engine misses

I havent don't anything as of yet, probably this weekend if i have time. I thought I could see if maybe the plugs were bad or something.