Smarty pants, I really could use your help! 350 Mag trouble SOLVED?? MAJOR UPDATE

Wildboating

Thanks everyone for all of your help along the way. 

212rowboat

I'm reaching...  it doesn't sound logical,  does it? 

Wildboating

It is the only thing I can believe at this time.  Looking forward to lifting hatch and see if if engine sounds under load like it was. 

Michael T

I agree there had to be more to it than that. However, a restricted exhaust can cause faults and possibly rpm reduction by the engine guardian mode?

212rowboat

i had a catalytic converter disintegrate once... not choke up over time, but straight up break apart catastrophically... I only ran the engine for a few miles when it happened, because believe it or not I pegged it instantly, though it was not something I'd encountered before... clog and fail, yes, but not go from fine to tossing chunks in a matter of minutes... turns out a massive amount of oil from a blown plenum gasket being ingested and dumping through the cylinders and into the exhaust is... uh... pretty **** a cat...

anyway... it gave me opportunity to see the drastic differences, not something that crept up on me gradually.  

it would run great up until I demanded load from it.  it would hit a wall at 3k or so, and it wasn't going to budge over that no matter what... it pulled fine up to that point.. the primaries on that rig were 3", which is sizable- maybe too much for the rest of the build, but I was building margin to grow when I chose those headers.  it has something to do with volume/velocity of flow- it's fine until it's not- interrupting the pulses and altering the direction allows it to push back on itself or creates (after a certain pressure is created) an area of high pressure the conveyer of pulses can't push through easily...

in another example- some fellas who boost without a wastegate or blow off valve, and who don't address exhaust size/dynamics, will experience a HUFF when they come off the skinny- it's not very noticable until you listen for it, and once you hear it you can't not hear it.  same concept... when the pressure relieves it huffs in one mighty push. some are so bad (think diesels with twin or compound turbos) sound like a hair dryer at idle- but later build enough pressure to clear the pipes- and all of this is without any obstruction but the exhaust itself..   

Black_Diamond

That rubber piece had to be an exhast flapper. 

212rowboat

Black_Diamond said:

That rubber piece had to be an exhast flapper. 

No doubt about it. 

aero3113

The restriction was your issue. I had it happen to me a couple of seasons ago.

raybo3

See I told you to swap the drives......LOL Glad you got it fixed must have been driving you nuts (no pun intended...LOL) Maybe the drive was installed wrong in the first place. Maybe the missing nut and bushing was causing the drive to "flex". Who knows but glad all is good. Now go and enjoy the boat for the rest of the season.

Michael T

Exactly!....exhaust flappers!

PartsMan

I'm pulling my boat in 2 hours. Hope to find my flappers in the exhaust too

Wildboating

@PartsMan. What makes you think yours are missing?  Low rpm?

reneechris14

3" piece must be  the flapper I swear you checked that before.but if it is fix go burn some fuel.yippee

PartsMan

@Wildboating - I have a water flow issue and I was missing 2 flappers.

Well I pulled the drive and no flappers. Used a camera and all is clear. I did find what appears to be a bracket, about 1" x 1/2". Dont think thats going to solve my problem, but haven't taken her for a run yet.

Michael T

Something must have been pretty hot to caramelize and eject those flappers. Maybe they were causing erratic behaviour and have now been blown out (hopefully)?

PartsMan

Their gone. Moving to the manifolds now ..........

Wildboating

Good luck @PartsMan I know the frustration all too well.

Wildboating

Do you have horizon closed cooling or standard raw water on your boat.  I assume you checked the impeller for your low water flow. 

Wildboating

Ok, still can't get over 3700 on starboard.  Last 35% of throttle isn't doing anything.  Ugh.  Guess it's time to actual hire a pro. 

Michael T

Agree!

Wildboating

Attempt number 1 with pro marine repair shop: found rotor cap was heavily corroded, replaced cap.  I took boat out and.... Not it.  Maybe ran slightly higher RPM, 3900-4000 starboard  / 4000-4100 port motor at wot.  But I rarely ever run boat by myself so the weight difference could possibly be the higher rpm.  22p, 1/8th fuel but full water and holding tank. Dumping tank tomorrow, hopefully they will figure it out soon. 

scan tool shows no power increase after 60% throttle still. 

Black_Diamond

Cap/rotor/wires/plugs. Both engines. 

212rowboat

heavily corroded cap?

corroded how?  

i learned a lesson this year from a mechanic who's been doing this for a long long time... what I had been puzzling on for hours, and hours after installing a brand spanking new cap and rotor over the same new spark plug wires i'd installed prior... 

it was ONE spark plug wire... I couldn't wrap my brain around it... he had to go all Barny on me to explain... I knew he was right because the engine was purring- but i couldn't explain why he was right... 

ONE wire causing sever resistance is all it takes, apparently- and the one in question, which i ultimately found, was brand new fresh out of the box high end 8mm... the other 7 were fine... the ONE wire resisted above a certain RPM (in my case about 2500rpm) and allowed spark to spray- and it sprayed until it found another place to ground- which happened to be the adjacent pins to adjacent cylinders.  the particular wire was wire 6, and the misfiring was following to 3 and 5 harshly, but upsetting the entire apple cart, so to speak, in such a way that it was as if it simply hit a wall- running great in RPM up to a point, and then abruptly falling off... 

I pulled the cap before this guy showed up, and found it to be upset- and figured I'd got a bad cap... so, a run to the parts store and return with a new cap----- five minutes later, the precise same thing... the spark spraying is hard-on caps and rotors.  I would have looked at it and thought "another bad cap".... it wasn't... this mechanic guy rolls up on his harley, with his helmet and backpack still on walks up beside the boat where me and another buddy are puzzling over this things and says (he's from New York) "yo, you'ze got a bahd wiyer"..... I'm thinking "nope, brand new MSD 8mm".... but he was right... 

I wager your issue is something similar.  it may be the same thing. 

Wildboating

Alswagg said:

I can't remember but have you performed a balance test while under load at WOT?   This can be done manually as well as electronicly with turning on and off each injector.  

We have not Al, however all injectors are new.  This balance test applies to the injectors correct?

Wildboating

Thanks 212!!  Very insightful and perfectly explained.   

Wildboating

The one thing that I can not get over, and I keep saying to the techs.  Listen to the engines!!!  The port motor sounds free and spins at a higher pitch.  The starboard sounds restricted, bound and at a deeper tone. 

212rowboat

huh... the sound....  

pull your CKPS out, wipe it down, and reinstall it being really careful about it's orientation... 

match the other one's orientation as closely as you can, just to see.  

sounds crazy? 

here

Michael T

I think Al is on to something the BTDC degrees, poor wire/cylinder......The timing light should be instructive.

Wildboating

Alswagg,  have not used a timing light however both motors cap at 24* via rinda scan tool.  Motors are 03's.  No new updates from "pro" dealer.  

Wildboating

Al, Cleveland is beautiful this time of the year