Hi,

i have a 454 Magnum MPI 1998. I bought the engine this summer and have now 2 hrs cruising with rich & rough idle when warm.

It gives fault codes 33 (MAP signal voltage too high) and 42 (Ignition Control Circuit grounded or open bypass).

Previous owner of this engine told that he has changed the distributor rotor two times, because of snapped rotor (Sierra). There is some marks of contact in old distributor cap, so it's clear that the rotor has touched the cap and then snapped.

So it is possible that the distributor shaft is loose or worn or something? Would it give fault code 42 if the shaft is worn?

Has somebody have the same trouble code 42? And if so what's the most often reason for this code? I think the code 33 is coming because of rough idle, sensor is new.

The reason i'm asking this is that i don't have access to the boat at now. The boat is lying in the dock of Mercruiser dealer but they have so much other stuff to do so i think i have to check it myself.

Pull distributer and look at bushing. I changed one earlier this year in a poor running boat. I will see if I can find it and post a pic. Worst I have ever seen. The bushing was oval.

AS soon as I seen broken rotor in the header of this thread --- I said It has to be from Sierra -- The info for all -- there was a Service bulletin on this as Sierra had a huge rash of broken rotors after installing them with some run time.

. The problem from Sierra was fixed last year at some point. But I do not use their ign stuff. Yes Merc is higher for the T bolt and EST stuff but guess what Merc makes some of the T bolt parts in florida. - (Merc does not make the EST set up ) - Buy USA stuff when you can. I understand that it is higher in price but I have found Merc cap and rotor is better than others for the T bolt 4 and T bolt 5.

Buy the Merc kit and if you need it - I have it all.

And of course if this does not fix the issue changing to merc stuff then you will have to look closely at the distributor for the issue and the install of it.

It's not a Tbolt distributor.

Did Seirra have rotor problems on the AcDelco external coil distributor Merc uses in the MPIengines ?

they had rotor problems sorry had EST and T bolt in there to but I edited it and its gone in my post.

Still confusing how you answered.

Did Sierra have problems with the rotor they sold for the EST (GM /AcDelco external coil distributor) ?
If yes, what was the issue ?

I had a pair of 502 mpi distributors with new sierra rotors and they wouldn't push on all the way, the keyway in the rotor was bigger than the shaft keyway, they would sit on crooked and make the electrode hit the cap, so I got a couple AC Delco ones from MAPA and the fit fine, no more issues, some parts being manufactured today are crap

Lots of parts today are crappy...trying being in the auto repair biz. Suks !

the main issues with bad rotors and a number of them would break was the EST rotor - Sierra brands. They had other issues with other rotors as well. The problems have been solved. Do not forget NAPA and O Rielly's sell Sierra marine parts as well

EST SIerra branded rotors had huge problems with those during certain production runs.

Thanks for the replies!

Is there any possibility to use some kind of aftermarket distributor? For example MSD 8366 https://www.summitracing.com/int/par...8366/overview/