[jay]

Team,

This is my first post and what an awesome site full of knowledgeable owners and technicians.  I have thoroughly enjoyed the info and intel I have been able to gather here.

Here goes my first post,I have a 1997 Tiara Open powered with 7.4 crusaders.  She was SOLID!  I would have motored to the west coast in her during the first 5 months of ownership. 

Then she ran hot trolling and blew out a cutlass bearing on the same trip. With all that said, historically I have broken down a few times due to over heating on both engines and limped in on one screw.  She hated trolling.  She hated idle........ 
 
Since then,  I have replaced the water pumps,  risers, coils, all belts, heat exchangers, cutlass bearings, replaced onboard charging system, new windless, and so on port and starboard.  All fluids, lights and such over the last year.  

NOW THIS....The boat temp and attitude are running good except for, on the Port side between 2000 - 2800 RPM's, the rpm gauge is bouncing from 1500 to 2800 rpms , but i don't hear a change in engine noise.  when i reach 3000 the gauge stops bouncing and holds steady. This wasn't happening before the riser, heat exchanger and coil were replaced though I can't see how they would contribute. 

This has been since day 1 as new owner.......At idle the starboard exhaust has a manly roar, while from the port side it is much more tamed.  While both engines fire right up, the Port side fires and sounds like my F150 and the starboard demands attention with a thundering rumble.  

Also the starboard motor pegs out at 4400 rpm and has a manly roar from the exhaust.  Now recently as the port side gets to about 3800 RPMs and as i give it more throttle, the rpm gauge creeps backwards like the engine is being bogged down.  The throttle gauges are not inline or parallel to run the same RPM's. 

I run or cruise everywhere ar 3200 and the boat runs perfectly, but she will not allow me to open her up like before.

Not to be long winded, but i wanted to give as much detail as possible.  Now i will wait patiently for the experts to diagnose.  All help is greatly appreciated.  I'm limitedly mechanically inclined at best.

Thank you in advance for your consideration and time.

JC

[sbw1]

My 454s used to get out of sync with different RPMS when the spark plug wires needed replacing. If we ran the boat with the engine hatch raised, you could see blue sparks coming from the wires. Changing the wires always cured the problem.

[Matta0413]

As mentioned above, Plugs and wires is a good place to start.

[jclark003]

If your engine has a knock sensor, a misfire in the engine can cause it to roll back the timing, giving you a lazy engine that will not reach full RPM under load. As previously posted changing plugs and or wires may clear things up. Also Your port tach bouncing around with no noticeable change in engine pitch points to a possible coil or tach issue. swapping the tachs from the good engine or the tach leads followed by the coil may help isolate things. The falling off at high end could be Restricted fuel delivery from a plugged filter, stuck anti-siphon valve or weak fuel pump.

Good luck and keep us posted

[Uhehner]

I agree with the above diagnosis. One more question. Are both props the same size P & D and can you spin the prop shaft by hand. If not you need an engine alignment. You say you changed the risers. Did you also do the elbows? When did you clean out the thru-hull valves? Critters love to live there and reduce the water flow. Also check the fuel tank vents. If they are plugged open the fuel fill caps and listen for a hiss.
A good mechanic should be able to adjust your throttle handles to within a 1/4" of each other. Lastly, a low water flow will cause the exhaust to be loud.
Capt. George

[RMS]

Have you checked/cleaned/replaced the U-coolers?  Pencil zinc residue in the U-coolers can obstruct water flow.  Also, there are three fuel filters per engine.  You can clean the primary 'hockey puck' filter.  The others should be changed.  Your current situation sounds like a fuel restriction.

[Uhehner]

I agree with the above diagnosis. One more question. Are both props the same size P & D and can you spin the prop shaft by hand. If not you need an engine alignment. You say you changed the risers. Did you also do the elbows? When did you clean out the thru-hull valves? Critters love to live there and reduce the water flow. Also check the fuel tank vents. If they are plugged open the fuel fill caps and listen for a hiss.
A good mechanic should be able to adjust your throttle handles to within a 1/4" of each other. Lastly, a low water flow will cause the exhaust to be loud.
Capt. George

One more thing to check besides the old zincs blocking the coolers is pieces of water pump vanes blocking the flow. Sometimes a back flush washes them out. 
Capt. George

[jay]

•  
  Team
  
• Thank you so much for your insight and time.  My mechanic states, feels, believes, that I have a bad cylinder and need a complete rebuild.  No even one of mentioned this as a possibility on here.  Any chance that could be the reason.  
  
• I asked him for a compression check but it hasn't been done yet.  
  
• With a bad cylinder or pistons or whatever what would be my tell tell signs
  

Thoughts

[jclark003]

A dead cylinder can certainly result in a lazy engine unable to hit max rpm. However it's hard for me to see it causing a roll back in RPM on the top end or a bouncing tach unless there are multiple issues with that engine (entirely possible).

Without a compression test done I'm not sure how your mechanic diagnosed a dead hole much less concluded a complete rebuild. Also poor compression often relates to valve issues rather than piston problems and pulling one head isn't nearly as involved as a major overhaul.

ive seen a lot of seemingly large problems be the result of something small and cheap. Make sure you throw a set of plugs and wires at it as previous posts have suggested and then go from there. Swap parts with your good engine if you aren't sure and want to test things. Definitely compression test the engine before going inside.

Best of luck and keep us informed.

[jrblough@mtu.edu]

I had a similar issue on a 89' 3300 open that I had with the Crusader 454's in it. The tachometer would just stop moving just below 3000 rpm or would bounce around. Was a dirty contact on the tach gauge itself....I could hear that the engine was running fine and continued increasing in rpm when I pushed the throttles forward... the tach just didn't work.