Baddogg

I Am Having A Problem With A 2000 496 Mag. It Has A Miss At All Rpm"s That As Of Yet Nobody Can Diagnose. Nothing Shows On Computer. Plugs Are New . Coils Are Good. Wires Are Good. Compression Is Good. What The F*%$#. Anyone Have Any Clues Id Be Glad To Hear From Ya! Motor Has 155 Hrs And Always Ran Great.

NJSONIC

Baddogg,
Have you checked your injectors? they will cause a miss if they are not working, or if they are spitting(not a fine spray patten).
Hope this helps.

Lmarth

Just a few points to get you started. Was the motor running smoothly and then started missing after some form of service? You mention new plugs, good wires etc. How do you know those items are "good"? New plugs aren't always "good". Assuming you have a good hard repetitive miss, the first thing I'd do is attach a diagnostic tach to the motor and start the engine. Note the rpm and start pulling the plug wires one by one before reinstalling the wire and moving on to the next cylinder. You'll probably find a cylinder where the rpm doesn't drop when you pull the plug wire. That will be your problem cylinder. Try another plug, plug wire, clean injector, make sure firing order is correct, pull rocker cover to check for cam lobe wear, bent push rods, broken valve spring (inner),etc. If it's a random,erratic miss, look at fuel system-fuel water separator, bad gas,etc. You're not throwing a code so it may be something simple if you're lucky. Just trying to help.

Offshore Addiction

one of your coils is bad or possibly the sensor coil!

halffast_2003

had a boat once that nobody could find the miss..it ended up being a slightly bent distributor shaft...pure luck finding it

Raylar

Badddog:
The advice you are getting here is pretty good. The Merc code readers won't really show single cylinder misses. Start with the simple plug wire test one cylinder at a time until you isolate the cylinder that does not change when you pull the plug wire. Then check for spark at that plug wire. If you have spark, change that plug with an adjacent cylinder and see if the miss moves. If it does, the plugs bad, replace it. If miss does not move then carefully pull up the green clip on top of the injector wire connector and unclip the connector from the injector by depressing the side plastic tang on the connector. If the miss does not get worse, your problem is a bad injector at that cylinder.You can also usually hear the injectors firing if you listen at each one with a tube or stethascope. These two checks will tell you which cylinder is missing, if its just one. Hope this helps, you can call me toll free at (866) 496-8181 8 to 5pm PT if you need more help.
Ray @ Raylar

Baddogg

thanx guys for the info im gonna have to go to injectors next because all the others check out good lets hope its just this thanx again

Comanche3Six

I would still be looking for that one

Baddogg

seems to have been an injector after all might have had something caught in it almost impossible to find hoping that was the problem thanx for your input

Island Hopper

Baddogg,
There have been alot of problems with the inlet screen of the boost pump getting clogged.
Unfortunately, this set up has the fuel line from the tank, running to the boost pump before it flows through the filter. There is a screen in the inlet side of this pump, that in notorious for getting clogged, causing fuel starvation. Mercury has since added an in-line filter to prevent this problem. The Mercury filters are a little pricey, and we decided to go with a Racor canister filter. In my case we were not able to figure this out until after it had already worked into the injector screens. If this has happened in your case, you will be able to determine this by checking the plugs. They will be soaked in fuel, and have a heavy carbon build up.
Good luck, let us know what you found.