1996 Mercruiser 3.0 Litre missfires

after the engine runs at cruise speed 3800 RPM's for 30 min's it starts running bad, skipping like it was crossfiring and finaly dies but will restart. I changed out the coil and it ran great again for 30 min's and starts the hole thing over again.
I have changed the fuel pump with an electric pump,gas filter and all new fuel lines.
also a tune up with cap,rotor,dist pickup coil,and control modual and last but not least new ign. coil
also went though the carburator two times
had the Alt. checked and it is working fine. 14.77 v
The coil has 13.17 volts going to it. at 2000 rpms
when it starts acting up I can change out the coil and it starts right up and runs great for the next 30 mins or so. I have not tryed yet adding gas to the carb when it starts this. I'll need to take it to the lake to try that. that will be my next atempt. Any ideas are greatly apreciated Thanks

Re: 1996 Mercruiser 3.0 Litre missfires

The coil has 13.17 volts going to it. at 2000 rpms

Click to expand...

Is your coil getting real hot when it starts to spit and sputter? If you have points ignition, check your resistance wire. Should be reading between 1.8 -2 Ohms...

Re: 1996 Mercruiser 3.0 Litre missfires

It has digital electronic ignition system
yes the coil does seem a little hot.

Re: 1996 Mercruiser 3.0 Litre missfires

It has digital electronic ignition system
yes the coil does seem a little hot.
I was told to check the spark when it is doing it
to see if it is blue or yellow I have not been to the lake yet to try it.

Re: 1996 Mercruiser 3.0 Litre missfires

catchandfryfisherman said:

It has digital electronic ignition system
yes the coil does seem a little hot.

Click to expand...

Well you have the EST (Electric Spark Timing) system because you did say you replaced cap and rotor. No resistor wire on that one...

Re: 1996 Mercruiser 3.0 Litre missfires

Do you have the Mercruiser service manual? If not download it here.

http://www.4shared.com/document/Ou0ZU3_4/Mercruiser_Service_Manual_13_G.htm

Go through the troubleshooting section of the coil with an Ohm Meter...

Are you running good gas? Check for sediment in your gas tank.

Check and make sure your vent hose for your tank is not clogged up or pinched...

Re: 1996 Mercruiser 3.0 Litre missfires

It is a lot harder than just a sputter. it jump and bucks like the dist. cap is wet but it is dry and I can't find any trace lines in the cap or rotor.
I will take my thurmal gun with me next time. Thanks

Re: 1996 Mercruiser 3.0 Litre missfires

Vent hose is clear and all gas is brand new and the tank is clean enough to eat lunch in it. spotless. thanks for the download though.