454 pinned at 3k rpm at WOT

[Jwing128]

Hoping some one can help me out here I'm frustrated beyond belief. 97' sundancer 290 with a single (unfortunately) 454 w/ bravo 1. Serial number OK004015. I was having an issue after the second start of the day where when trying to accelerate over 2000 rpm engine would bog down and die. Decided to swap out the fuel pump and throw on a new edelbrock 1410 carb. Then started to think I needed to replace the exhaust so I might as well have it done at the same time. The manifolds were so old and rusty the bolt heads broke off in the heads. Had the heads pulled and reconditioned.

We finally got it back together with new :
-manifolds risers
- fuel pump
- impeller housing kit
- spark plugs and wires
- edelbrock 1410 carb
- heads reconditioned

Took it out yesterday for the first time. Starts right up, idles okay but fluctuates from 750 rpm to 1100 every once in awhile. Under load yesterday at WOT the tach was pinned at 3k and the bow was straight up. Wouldn't get on plane and just stuck at 3k barely moving. It's not a prop issue because nothing has changed with the prop and when we bought it 7 months ago I had it running at 4400 around 25 knots. Checked that the plug wires aren't crossed this morning and revs over 4k in neutral. Driving me nuts after all the time and money spent. There may be a small amount of buildup on the hull but I wouldn't think drastic enough to result in this. Any thoughts or suggestions would be greatly appreciated.

Sent from my SM-P600 using Tapatalk

 

[dvx216]

sounds to me you need to find out what your fuel pressure is and that would eliminate your fuel system.Go to auto zone and rent their fuel pressure kit.Not mentioned but have you changed your fuel filter.Also anti syphon valve at tank and check pickup tube in tank and make sure your tanks vent is not plugged and easy way to do this is run the boat with gas cap cracked loose if your problem goes away its your vent.

 

[Thornton69]

Hoping some one can help me out here I'm frustrated beyond belief. 97' sundancer 290 with a single (unfortunately) 454 w/ bravo 1. Serial number OK004015. I was having an issue after the second start of the day where when trying to accelerate over 2000 rpm engine would bog down and die. Decided to swap out the fuel pump and throw on a new edelbrock 1410 carb. Then started to think I needed to replace the exhaust so I might as well have it done at the same time. The manifolds were so old and rusty the bolt heads broke off in the heads. Had the heads pulled and reconditioned.

We finally got it back together with new :
-manifolds risers
- fuel pump
- impeller housing kit
- spark plugs and wires
- edelbrock 1410 carb
- heads reconditioned

Took it out yesterday for the first time. Starts right up, idles okay but fluctuates from 750 rpm to 1100 every once in awhile. Under load yesterday at WOT the tach was pinned at 3k and the bow was straight up. Wouldn't get on plane and just stuck at 3k barely moving. It's not a prop issue because nothing has changed with the prop and when we bought it 7 months ago I had it running at 4400 around 25 knots. Checked that the plug wires aren't crossed this morning and revs over 4k in neutral. Driving me nuts after all the time and money spent. There may be a small amount of buildup on the hull but I wouldn't think drastic enough to result in this. Any thoughts or suggestions would be greatly appreciated.

Sent from my SM-P600 using Tapatalk

Were you able to identify what your original problem was or was all this work and parts done hoping for the best? Have you done anything with your fuel supply system (tank, lines and water separator)? Have you tried supplying fuel from a second source?
25 knts @ 4400 sounds like it is giving it's all to hold it up. If your boat is heavy for what you have for available power, then you will be surprised with the difference a clean bottom will make. Correct trim of outdrive and tabs as well can make the difference of getting up or not if available power is limited.
Fluctuating idle sounds like a possible vacuum leak or incorrectly tuned carb. Have you checked manifold vacuum and tested for leaks?
Since all the work was done, have you checked compression? Hydraulic lifters can easily be set incorrectly.
Did you confirm correct plug gap and check your timing at full advance?

 

[dwna1a]

Does this engine have a ignition control moduale (thunderbolt ICM)

 

[Jwing128]

sounds to me you need to find out what your fuel pressure is and that would eliminate your fuel system.Go to auto zone and rent their fuel pressure kit.Not mentioned but have you changed your fuel filter.Also anti syphon valve at tank and check pickup tube in tank and make sure your tanks vent is not plugged and easy way to do this is run the boat with gas cap cracked loose if your problem goes away its your vent.

Fuel filter was changed 4 months ago. Thanks for the suggestions I'll check the fuel pressure and anti siphon. People keep tell me they think it's buildup on the bottom but I just can't imagine that much power degradation from a few months in the water.

Sent from my SM-P600 using Tapatalk

 

[Jwing128]

Were you able to identify what your original problem was or was all this work and parts done hoping for the best? Have you done anything with your fuel supply system (tank, lines and water separator)? Have you tried supplying fuel from a second source?
25 knts @ 4400 sounds like it is giving it's all to hold it up. If your boat is heavy for what you have for available power, then you will be surprised with the difference a clean bottom will make. Correct trim of outdrive and tabs as well can make the difference of getting up or not if available power is limited.
Fluctuating idle sounds like a possible vacuum leak or incorrectly tuned carb. Have you checked manifold vacuum and tested for leaks?
Since all the work was done, have you checked compression? Hydraulic lifters can easily be set incorrectly.
Did you confirm correct plug gap and check your timing at full advance?

My first attempt at fixing the initial issue was a new fuel pump, which started the snowball into exhaust, carb, coil, heads inadvertently. I can say the initial problem appears to be fixed however I can't say which service did. It's a heavy boat and seriously under powered, but not THIS under powered. I haven't done anything with the fuel supply system but that should be my next task, fuel supply and pressure check. Mechanic is coming this week to check the timing and compression. I know I need the bottom cleaned and repainted but it's a pricey service and I'd hate to do it first only to end up with no improvement and it end up being a simple fuel delivery or ignition issue. I'll start with troubleshooting those first and let you guys know the results.

Sent from my SM-P600 using Tapatalk

 

[Jwing128]

Does this engine have a ignition control moduale (thunderbolt ICM)

That's a good question I know other people have had similar issues with the ignition modules. How can I tell or where would it be located?

Sent from my SM-P600 using Tapatalk

 

[hottoddie]

Don't underestimate how much a growth can accumulate on a boats bottom in a few months, especially if the boat is not used on a regular basis. Growth on the drive and prop will make the problem even more dramatic.

 

[dwna1a]

I'm stuck here recovering from heart surgery. According to all I've read you do have a ICM. Let me see what I can fined tonight

Im one of those who had this issue

 

[Jwing128]

I'm stuck here recovering from heart surgery. According to all I've read you do have a ICM. Let me see what I can fined tonight

Im one of those who had this issue

Heart surgery wow. Really appreciate it. Let me know what you find.

Sent from my SM-P600 using Tapatalk

 

[Jwing128]

Don't underestimate how much a growth can accumulate on a boats bottom in a few months, especially if the boat is not used on a regular basis. Growth on the drive and prop will make the problem even more dramatic.

It's used 3/4 times per month. Definitely need to have the drive, prop, bottom scraped and painted. After a few minutes at almost WOT I could feel the boat vibrates a little. WOT @3k pushing 10 knots with a slight vibration is super frustrating after the time and money spent lately. As they say, Break Out Another Thousand. .

Sent from my SM-P600 using Tapatalk

 

[hottoddie]

Clean the prop and drive unit and you will see a dramatic improvement. Make sure you clean out the drive unit water intake or you will be overheating.

 

[NorCal Boater]

This may be a stupid question but with all of the work you had done....are you sure the throttle is opening all the way? You changed the carb and even tho you may think the throttle handle is pushed all the way forward maybe there is still some left on the carb.

Shawn

 

[sr330daguy]

This may be a stupid question but with all of the work you had done....are you sure the throttle is opening all the way? You changed the carb and even tho you may think the throttle handle is pushed all the way forward maybe there is still some left on the carb.

Shawn

Also make sure the secondary's are opening. If memory serves me ,I think they may be locked out until the choke is completely open.

 

[CliffA]

you may have a dead cylinder due to a bad spark plug or plug wire......that can cause you to loose 1,000 rpm....just went through this with my boat....I had a bad fuel injector on the starboard engine that kept the engine from revving past 4,200 when the WOT for my engines is 5,200.....

the vibration you are feeling at WOT may actually be the engine misfiring due to the dead cylinder......

cliff

 

[dwna1a]

Before I start, forgive my spelling. Double check all of the previous work. Go online and look up the timing system for a Merc 454, this way you will know the look of the part. My ICM is mounted to the raiser and its wires run back to the distributer. The ICM can be tested and is a pricey part. It sounds as if this is the problem from what you've written. Once the unit heats up it shuts the motor down, starts and runs until the rpms increase past 2000 then bogs down. Once the unit cools down it will do the same thing over again. The ICM controls the advance of the engine once you push the motor past that 2000 mark.

Once you you figure out that the ICM is bad sit back and think (I wish I had) do you replace the ICM or replace the system. In my case I replaced the ICM and bought a spare. It's cheaper to replace the system, but that's your call.

If if you go with replacing the system and your a great gear head you can save money by doing it yourself. If not hire the job out and not to just to the guy on the corner. I use one shop to do all the work on my twins they are Merc mechanics. Don't forget you messing with the timing, one little move in the wrong direction and she will run like crap.

 

[Skybolt]

Do yourself a favor and do a compression check before you do another thing. Then make sure all eight plugs are firing, your coil could be the culprit if you have good compression.

When you said the manifolds are that old, water could have leaked in the exhaust. A simple compression test will tell you a whole lot. Good luck.

 

[rcknecht]

Don't underestimate how much a growth can accumulate on a boats bottom in a few months, especially if the boat is not used on a regular basis. Growth on the drive and prop will make the problem even more dramatic.

I had this happen to me with growth on my props...

 

[dwna1a]

I also see you replaced the raisers. Check the wiring and plug leading to the ICM, it may just be loose.

 

[Jwing128]

I'm going to check the carb and throttle cable when I get home tonight. Having a diver come on Friday to scrape the bottom and my mechanic come to check the timing. If I understand correctly I can check for a bad plug or wire by removing a wire at the distributor cap and checking for a drop in RPM's, do one at a time until you remove one that doesn't result in a drop. Really appreciate the input, hopefully will narrow it down by process of elimination.