replaced ignition sensor and coil but now.........

[namniar79]

problem started last saturday boat was starting great and running like it should and then would not start. Replaced ignition sensor, cap, rotor button, and coil. starts great but now the engine has a loss of power. will not go above 4200 rpm while in gear or under a load if you will. Engine is running smoother than ever. Could i have a bad sensor or coil Is this a likely problem? The new sensor has a ground wire where the original did not so i grounded it to the coil mount bolt. 2000 model 5.0efi.

 

[namniar79]

should i unhook the battery to reset the ecm. Any help would greatly be appreciated. thanks. ray

 

[namniar79]

put the old coil back on and i have the same problem. so all i have changed is the sensor and cap and rotor. could i have a timing issue from the sensor and yes the wires are correct to the plugs. what am i missing?

 

[CliffA]

i would suggest checking the ignition timing as a start....if that does not fix the problem post back for other ideas....does the engine seem to be cutting out when it hits 4200 rpm's?.....if so we will have to determine if the problem is electrical or fuel supply related....

cliff

 

[namniar79]

thanks for your reply. it seems to have good power till about 3000rpms and kinda starts to fall on its face . by this time the boat is on plane and gets to 4200 trimmed out to proper cruising speeds. but still runs smooth. how do i put the engine in base timing mode. i read about a purple wire but not sure where to look or if my ignition is the same as what i read. Not sure what ignition mine has but the engine serial # is ol624937.

 

[namniar79]

i noticed that since i bought the boat last year that when the fuel pump pressurizes its not smooth. changes pitch several times. I'm starting to lean that direction. when i replaced the fuel filter it would start and run for a bit then die it may be typical but it had plenty of time to fill the filter but did not completely until i screwed it back on after inspecting. gonna get pressure checks sometime this week. what kind of reading should i expect I'm guessing it will be the same pressure at all rpms and where should i hook the gauges? thanks again!

 

[CliffA]

can't help you on the fuel pressure question since my engine is carb'd.....someone else will likely post the answer to that question....

you probably have a Mercruiser 'Thunderbolt' ignition system....it is important to know what generation you have....most likely it is either a Thunderbolt IV or V.....do any of the stickers on the flame arrestor cover say which ignition you have?.....this is important because the methods to set the ignition timing may be slightly different for each generation of ignition system....since your boat is a 2000 year model i bet it has the Thunderbolt V ignition......

also, i know you mentioned this in your first post, but you should include what year your boat is in your signature and/or your profile details...that is helpfull info for the forum members to have so we can help you with future posts...

cliff

 

[dwna1a]

Just to add to Cliff's posting both the Thunderbolt systems have a set of numbers stamped into the housing. You must have the correct one. Those numbers tell you the amount of advance each will do

 

[namniar79]

i have solved this issue. i replaced the new ignition sensor with a new one from old stock. i believe it said cherry on it. anyway i think that the new sensor may have been one for a 4.3 but not sure if they are the same or not. The first new sensor replacement was the issue. Thanks for taking the time to help me!

 

[3672 Sexpress]

Did you solve this problem? My port side 454 horizon MPI does the same thing... tops out at 4200. I put a diacom on it (and the stbrd side) and you can see that the port side is taking more throttle than the stbrd side starting from about 1500rpm on.

 

[namniar79]

i actually replaced the sensor with an new old stock sensor. not the new design. that seemed to fix the problem.

 

[namniar79]

i actually replaced the sensor with an new old stock sensor. not the new design. that seemed to fix the problem.

to new findings on the newer sensor style...the timing was off and so the distributor had to be unclamped and turned slightly to adjust it back right. problem completely fixed.