07 350 mag mpi misses help please

had a problem of no power after 3/4 throttle and reading some of the old posts here lead me to change the cap, rotor, wires, and plugs. it has the thin cap on it. i ended up replacing the cap with an accel cap from advanced auto. put it all together and the boat had a miss. checked the wires again and had 2 crossed. started boat up and it ran great. made som dead stop to wide open throttle runs and rpms were perfect and boat ran super. idled around the lake and on way back made prob a mile wide open pull with no problems. when i pulled the throttle back down to idle speed the boat again developed the miss. pulled wires off and now it's on the opposite side of the motor not firing. i have not done a compression check but will. a question of mine is this, did putting an accel auto cap on it instead of a marine one be my problem? i know these caps can burn thru to other pins and cause problems. vehicles don't usually run at top rpm for very long so would it possibly have burnt thru to cuase plugs to fire at the same time? what is weird when i pull the wire off that isn't running the boat actually runs smoother. help or advise would be great. thanks, brian

Stick w/marine electrical parts parts. You may need a new set of plug wires. Pull the cap off and look for moisture and carbon tracking. Are you sure all of the injectors are firing?

I have replaced the wires. I will get a marine cap. I did look at the bottom but no moisture or carbon. My old one didnt have any either. Can the cap burn thru where you wouldn't see it. Haven't checked the injectors but the boat was running great. When i pulled throttle back it sounds like i have 2to crossed wires again.

Never seen one burn thru...seen cracks, carbon tracks and burned electrodes.

I have replaced the wires...it sounds like i have 2to crossed wires again.

Click to expand...

What wires did you use? Did you replace the coil wire? Are they crossed causing them to crossfire?

are you sure the wires are connected properly to maintain the correct firing order?

could be your vac advance on the dis sticking. after wide open then dead slow if advance not going back then timing will be off.

Mercruiser wires. Checked the routing of the wires 3 times all are right. Where is the vac advance? Baffling how it ran perfect then pull throttle back then like crap

under the plate where your points are. at high rpm the points move to stay in time the firing of the spark plugs at hihgt RPM when you slow the RPM the points should move back. But if they are sticking then your spark is not in time with the low RPM but still at the hight RPM setting.. Dose that make sence

Yes that makes sense. The boat has electronic ignition on it though.

Marine engines do NOT have vacuum advance especially EFI....................disregard that post/question.

Is there no spark advance on electronic igition ? Sorry I will keep my mouth shut

There is a advance but it is either mechanical (old point ignition) or electronic advance ( all electronic ignitions 4 6 and 8 cylinders) and electronic for EFI (computer controlled).


Only automotive used a vacuum advance.

Until EFI there were not any vacuum ports on a marine engine. that was one of the things that seperated a marine carb from a automotive carb.

at least as far as I know.............and no need to shut, just make sure you have your facts correct when trying to help others so they are not looking for ghosts................

I should have called it a counter weight advance. That's what I ment. My boat was doing almost the same thing. The weights where all rusted up

Update, so i took off the accel cap and rotor and replaced it with mercruiser parts. Now the boat is firing on all cylinders again and running good. Guess i learned my lesson about trying to use car parts for a marine application. Thanks for all the help.

Not sure as to exactly what distributor you have in your boat, I assume it is a merc, and one used on EFI type motors.

I do not have any personal experience with this year boat/motor,

Was the Accel cap designed as a replacement for the merc?

Also I am not sure that automotive used the same dist. as marine........I do not know this but it may be so.

Remember, One thing most here who try to help others. We almost all the time reccomend OEM parts over aftermarket for critical components.

1. Coast guard approved.
2. OEM almost 99% of the time fit right and perform as designed.
3. sometimes there are subtle changes for marine that are not present in a automotive version.
4. When working for a marine repair business and your service is 99% mercruiser and 99% of replacement parts are purchased from mercury you use OEM PERIOD. Thus typically no relevant opinion on NON OEM parts.....


I always suggest OEM............If not asked when doing a repair...........only OEM..........

The cap is the one i think they call the dizzy cap. It's thin with the wires that enter the side. 99 chevy has the same cap and thats what i tried to replace it with. Luckily advanced auto took it back without any questions.

GM calls that design a crossfire cap...has molded in wires between the rotor interface terminals and the spark plug lead connections...

using the wrong cap will perturb the cam retard parameter and adversely impact engine performance and inhibit running if it is too far off.

Heed the words of Kghost and you won't go wrong...