350 mag sounds like it's missing, but runs great..

[mjfink]

Got a new boat with a 2006 350 Mag (MPI) with B3 and, in general, it's running great. At idle the boat sounds perfect. Comes up on a plane easily and not giving me any indication of something being wrong.

However, when on a plane (at high speed only) there's a sound that I think sounds like "missing". RPMs don't seem to move and the boat doesn't seem to surge (or drop). This boat is new to me, so, for all I know, it's always been like this.

I'm wondering if I'm hearing the exhaust broach the water and that's what I'm thinking is a miss? It just doesn't seem to SOUND (not feel, it feels fine) smooth when it's on a plane. Now, I realize, this is a very general and non-specific description, but does anyone else have some insight to share about this engine ("mine sounds like that too")?

Thanks for any help!

 

[Bondo]

Re: 350 mag sounds like it's missing, but runs great..

Got a new boat with a 2006 350 Mag (MPI) with B3 and, in general, it's running great. At idle the boat sounds perfect. Comes up on a plane easily and not giving me any indication of something being wrong.

However, when on a plane (at high speed only) there's a sound that I think sounds like "missing". RPMs don't seem to move and the boat doesn't seem to surge (or drop). This boat is new to me, so, for all I know, it's always been like this.

I'm wondering if I'm hearing the exhaust broach the water and that's what I'm thinking is a miss? It just doesn't seem to SOUND (not feel, it feels fine) smooth when it's on a plane. Now, I realize, this is a very general and non-specific description, but does anyone else have some insight to share about this engine ("mine sounds like that too")?

Thanks for any help!

Ayuh,... My waGuess is it's goin' Lean at Wot,.... Could be Detonation happenin'.....

Check the fuel filter for water, 'n put on a new 1, then try it....

 

[mjfink]

Re: 350 mag sounds like it's missing, but runs great..

Bond-o,


Excuse my ignorance, but does the 2006 MPI motor use the same "spin on" filters that my older TKS used? I still have 2 of them floating around, so I could try that pretty easily. The Quicksilver filters I have look just like an oil filter (they are cheap, like 10 bucks each).

My engine serial number is: OW370643

 

[brandon110]

Re: 350 mag sounds like it's missing, but runs great..

Check the distrubitor cap for build up on the contacts. if there is some at high speeds it can miss that cylinderor cross fire to the next cylinder inline if that is path of least resistance.

 

[mjfink]

Re: 350 mag sounds like it's missing, but runs great..

Cap was just done (and it was like this before the cap was done as well). Plug wires haven't been done yet, so that's a possibility. Would they fail to deliver enough spark only at higher engine speed (could that happen)?

Spoke to my mechanic and he said could be TPS or CPS...

More than anything, I'm wondering if I'm just getting used to the boat. The RPMs aren't really jumping around when this happens. I wonder if this could just be a "normal" feeling on this boat.

Check the distrubitor cap for build up on the contacts. if there is some at high speeds it can miss that cylinderor cross fire to the next cylinder inline if that is path of least resistance.

 

[dubs283]

Re: 350 mag sounds like it's missing, but runs great..

Spoke to my mechanic and he said could be TPS or CPS...

no way to tell that without using a cds or ddt

TPS maybe, ive seen that on outboards at high rpm but with noticable runnabilty issues

CPS, 99.9999999% its not that, they either work or they dont and you would know if it wasn't working

the only way to tell if you are having a higher rpm issue without noticable runnabilty issues is to run with a cds connected or a recorder and playback in a cds program and watch for any abnormal data list/graph items

 

[brandon110]

Re: 350 mag sounds like it's missing, but runs great..

the wires on those motors with my experiance rarely go bad. If it was your cps you wouldnt have a tach signal. if your tps failed you would get a engine alarm. unless it failed in range which could happen. I have seen on some of these the coil go bad. there is a wire harness that goes from i belive your coil to the module right next to it that has a pink wire and i belive a black wire in it. on the pink wire there is a 7 OHM resistor check it i have only heard of one going bad but the running issue it had was a high speed skip

 

[mjfink]

Re: 350 mag sounds like it's missing, but runs great..

Man.. The boat I just sold (to buy this boat) had a coil problem. I feel cursed.

Tach is fine (and, even when I feel the "cutting out", seems to remain at the same RPMs).

Should I just follow the Merc instructions for troubleshooting the coil as the next most likely step?

the wires on those motors with my experiance rarely go bad. If it was your cps you wouldnt have a tach signal. if your tps failed you would get a engine alarm. unless it failed in range which could happen. I have seen on some of these the coil go bad. there is a wire harness that goes from i belive your coil to the module right next to it that has a pink wire and i belive a black wire in it. on the pink wire there is a 7 OHM resistor check it i have only heard of one going bad but the running issue it had was a high speed skip

 

[brandon110]

Re: 350 mag sounds like it's missing, but runs great..

Yea id test the coil. but first did you try ne spark plugs?

 

[mjfink]

Re: 350 mag sounds like it's missing, but runs great..

Yea id test the coil. but first did you try ne spark plugs?

Yup, plugs are new. Wires aren't new, so I suppose that could be it as well. I don't think it's fuel delivery because the engine runs so well at lower RPMs and it never "dies", it's just "stuttering". It doesn't even feel like it's losing power, so I'm thinking I've just got a cylinder that's missing occasionally (and if it's the coil, it would just be a random cylinder that's missing).