Hesitation and cutting out with 454 HELP PLEASE!!!

[jrspawn]

Hello, i recently picked up an 87 baja 240 with a carb'd 454 that im having some problems with. Just the other day out of the blue it starting missing bad under a load. While either taking off or at WOT in the water it misses, sometimes causing the engine to die out. It runs great at idle, or running on the hose out of the water. Another thing i noticed is that while running it in the ranges it misses, if i adjust the trim or trim tabs it feels like the whole boat is coming to a stop. The engine almost cuts all the way out. Both batteries are new and at idle they show to be charging around 13.4 volts. Engine off the test 12.5 volts.

I have replaced the stock mercury distributor cap and rotor, installed new AC plugs, and MSD plug wires. This made no difference!

If you leave the boat idle for a while and go to take off, its worse than if your running mid throttle and opening it up.

Any help is GREATLY APPRECIATED!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thank you
Justin

 

[26aftcab454]

Re: Hesitation and cutting out with 454 HELP PLEASE!!!

Check Fuel Pump / filter/ water separator

 

[jrspawn]

Re: Hesitation and cutting out with 454 HELP PLEASE!!!

I also changed the fuel filter/separater. Its weird but it just doesnt seem like a fuel issue. It does not backfire at all either, just flat out misses. With the engine wanting to cut out when anything electrical is used(trim, trim tabs, etc) while missing makes me lean even more towards the electrical side of things...

 

[picklenjim]

Re: Hesitation and cutting out with 454 HELP PLEASE!!!

Check how much voltage you are getting on the + side of the coil. Then see if it drops a lot while running the trim. Could be the resister wire from the key to the coil is bad.

 

[jrspawn]

Re: Hesitation and cutting out with 454 HELP PLEASE!!!

What type of voltage should i see there at the coil, and how much if Any drop in voltage while operating the trim is "ok"?

Thank you

 

[picklenjim]

Re: Hesitation and cutting out with 454 HELP PLEASE!!!

Not really sure of that as the manual doesn't give a spec for voltage. They tell you how to check the resistance wire in ohms. In mercury manual #9 it tells how to test it on page 4B-7 and how to replace on page 4E-4. If you don't have this manual you can download it from the ADULTS ONLY section at the top of the page. It will be on the Mercruiser Information page under manuals.

 

[picklenjim]

Re: Hesitation and cutting out with 454 HELP PLEASE!!!

There is also a diagram on page 4C-2 which shows the system componets. You can see how the resistance wire is in the circuit. It supplys a lower voltage to the coil when the key is in the run position. Another purple wire goes from the coil + terminal and down to the starter sloenoid. It supplys full voltage to the coil when the key is in the cranking position.