370DA owners – Are resonators installed in your exhaust hoses?

[kap2]

1998 370DA, 7.4L MPI MIE L29 Gen VI engine, v-drive, standard “log” style thru hull exhaust...

I’m in the process of replacing manifolds, 3” risers & elbows and have read the Merc Service Bulletin 2001-13 where it describes water being drawn backward into the exhaust passage during engine idling. The bulletin claims that using the Exhaust Resonator Kit, 860222A1, in the exhaust hoses will help stop the ‘tuning’ affect that is causing the backward draw of the cooling water.

Currently, the resonators are not installed and I was wondering if other 370DA’s have them installed and if they can be used in this system. Or is there another fix that would resolve the issue like a different exhaust set up?

Thanks!

 

[Sea Ray Mark]

Resognater didn't work for me, had to go with 6" risers and new exhaust system to fix the problem. I complained to sea ray about it a few times and they sent me a new exhaust system but don't think they would do that any more.

 

[Sea Ray Mark]

Sorry, forgot to mention my former boat was a 1998 370DA

 

[kap2]

Mark, thanks for the reply. Do you recall what type of exhaust you installed?

 

[kap2]

bump

 

[Sea Ray Mark]

It was the 380DA style system which has a drum type muffler.

 

[rondds]

I haven't heard much about problems with 370DAs and ingestion. That problem seemed to arise with early ('99,00,01) 380DAs with 7.4s (also 340DAs & 410DAs of same vintage and same engines). The exhaust system was redesigned in incorporate water-lift mufflers and the problem was pretty much eliminated with the advent of the 8.1s.

 

[Knot It]

I also think it was primarily in the higher hp (380hp Horizon's) as apposed to the 310hp 7.4's.

 

[rondds]

Yes. Gen VI I believe. Had something to do with valve overlap that GM set up with those engines.

 

[Sea Ray Mark]

As far as I know the problem only existed in the 380hp Horizon motors because they increased the duration of the cam that helped the horsepower output but created a condition were the intake valve would begin to open before the exhaust valve was fully closed. This created a pulsing in the exhaust that caused some of the exhaust water to slowly creep back up into the manifold at idle. When this happens you'll begin to notice a sheen on the water from unburnt fuel but the engines will be idling fine since the computer will compensate for the cylinders that aren't firing. If you rev the engines you will notice a distinct stumble which will confirm you're running on less then 8 cylinders. If you hold them at high idle of 2000rpm or so for several seconds they will clear out and start firing again. The other issue I've heard of was caused by the long exhaust hose runs from the elbow back to the log style muffler. These sections didn't have enough pitch on them and in some cases if the operator back off the throttle very quickly while on plane the exhaust water would rush back up the hose and the engine would ingest a big mouthful of water. I hope this helps, Mark

 

[rondds]

That's exactly my understanding of it. You put it so eloquently Mark!

 

[kap2]

Thanks for the feedback!

I have a 1998 370DA, 7.4L with 3" riser spacers and the original "log" style muffler and no in hose resonators. I just removed the manifolds, risers and elbows and found a small amount of water in the exhaust ports of the manifold. There weren't any signs of leaking at the riser or elbow joint. I'm thinking this maybe due to the "reversion" action that can happen during long periods of idling (Service Bulletin 2001-13). What is the best way to resolve this issue?

1. higher riser extensions - 6"?
2. "water lift" style exhaust system?
3. add the in hose resonator?

 

[rondds]

I'd think the BEST way is choice 2. above, but I'm sure that's the most expensive route.

 

[74Alfa]

Great info in this thread. I'm a 380DA owner and just purchased two new 454 long blocks (Gen VI, 380 HP) for a re-power. I'm assuming I have the water-lift type exhaust since there's a large upright can in the middle of each system but I'm not sure if there's a resonator in the tubes yet...