496HO, high rpm miss ????Any ideas?
 

Over 4500 rpms I have a miss, not all the time.
150 hours, been doing it since new. Had 2 dealers
check for codes, nothing, water filter changed,
sparkarrestor cleaned. Different fuel. Same problem.
Took it out last night, got one good run and it cut out
after that. Seems like fuel starvation, any ideas?
Mercury tech have a number? Thanks JC

I remember someone last year with 496HO having problems that were related to the crank trigger/sensor. It was a long investigation and alot of check this check that before they stumbled onto that. Not sure if it is related to yours but you may want to try a search and look around last summers posts.

Rick

Put a new set of plugs in and check plug wires

Thanks...
 

I'll try the plugs, probably time any way. Heard they cost a
fortune, for plugs. Merc said to get a scanner hooked up
while running. I'll see if I can get someone to do it. JC

The damn plugs are like 15 bucks a piece at most locations.
Good luck.

Did you check the crank position sensor...maybe a loose wire.

I would check your electrical system. Those Fuel-Injection systems require alot of voltage. If you have a bad ground or a thin cable, you may not be getting the required amperage through the system.

The batteries are installed by the dealer, so they may have put in cheap cables. You will want a large ground wire between the batteries and to the engine.

Good luck! :D

If you are just looking for random thoughts, when I read your problem description I thought fuel tank vent is not working. Could try cracking the cap when it is acting up to see if there is vacuum in the tank. Why else would you get one good run first?

Also, does the miss get worse if you try to trim the drives while at WOT? A lack of voltage or ground problem may make the miss worse when additional load is applied.

Good luck,

BT :cool:

I'll check these out..
 

Thanks for the help, keep em comin. Any simple things I
can check could help. The first run isn't always the good
one, it comes and goes. I back off when it starts missing
so I don't know about the electrical load. How can a plug
cost 15.00? Theres some stealin' goin on there.
The weather sucks here, havn't been able to check yet.
Thanks JC

Re: I'll check these out..
 

You think that's bad........wait until you check the price on the plug wires.:eek: :eek:

Been there done that. Check your fuel preasure. I had this happen to me on my first 80 hours. It turned out to be a bad pump. The miss would come and go. If you put a preasure gauge on it and run it under load on the water you just might find your problem. Mine would run fine out of the hole then after a minute or two the preasure would drop of to just 5 or 6 lbs. I believe it is about 42 psi you are after. The bad pump on mine was behind the fuel filter and mine was covered under warranty.