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454 330 hp Crusader will not hold rpm under load

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contender31

Regular Contributor
I recently bought a 33 foot Tiara Open with 2-454 330 hp crusaders with 1300 hrs, I ran the boat for several hours,then 1 day I was cruising at 3200 rpm and the rpm gauge on the starboard engine started fluctuating between 1k and 3 k and the engine would not carry the load of the cruise rpm. I brought it back to port and decided to change out the fuel filters on the hunch they were old and dirty. When I took them apart I noticed that the paint/coating on the inside of the filter basket was peeling off. I took the excess off, changed out the filters and o-rings with new ones. I took it out for a sea trial and the same problem exists. The engine will hold rpm in nuetral but will not under load - it appears like it wants to go but will hesitate and drops back down to 1 K rpm. I can run the boat all day long at idle but it will not carry the load on increased rpm. The temp gauge is constant at 150 degrees, the only thing I noticed unusual was the psi gauge was erratic periodically and then stabilized at 40. Any ideas /suggestions - new to inboards but fairly mechanically minded. Question - if the o-rings in the filter cartridge were not seated correctly - could that potentially be the problem?

Thanks
 
Not sure of the model year of your motors but i just went through a similar situation with my 2000 454 MPI's. Mine have a second black plastic "pancake" style filter next to the water/fuel filter. The pancake filter has a metal screen in it and mine was over 50% filled with sediment and "gunk." After cleaning the filter case and screen completely, the motors have been able to hold rpm at all times again.

i am by no means a mechanic and hopefully if anyone else has more knowledge they will jump in here.
 
Sounds to me like fuel starcation as well. Careful: that can eat a piston in no time. Change all of the filters to begin with--including any after the pump. If that doesn't do it the carb will need to be opened and cleaned. Again, don't let this continue or else!

Jeff
 
fastjeff said:
Sounds to me like fuel starcation as well. Careful: that can eat a piston in no time. Change all of the filters to begin with--including any after the pump. If that doesn't do it the carb will need to be opened and cleaned. Again, don't let this continue or else!

Jeff
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Thanks I changed the filters in both cannisters just after the fuel tank, are there others?
 
Thanks I changed the filters in both cannisters just after the fuel tank, are there others?
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It would help narrow things down if you can provide the year (+/-).

Yes, leaking o-rings will cause loss of suction if they are installed before the fuel pump.

The older quadrajets have screened filters at the fuel inlets.

Make sure the fuel shutoff valve is 100% open, too.
 
the year of the engines are 1990 - they have the older 4 barrel carbs non fuel injetced. The filters are between the tanks and the fuel pump I believe. I haven't gone as far as locating the fuel pump. Are you aware of the location of the fuel pump?
 
Contender,

You may have a problem with the vent on the gas tank. To test this just try running with the fill cap removed. You may also have a dirty/partially clogged anti-siphon valve which is located at the top of the fuel pickup tube on the tank. They can be removed and then cleaned by pressing in on the small steel ball while spaying with carb cleaner.

Good luck!

Erich
 
The filters have the Raco filters that are inserted into a round metal filter cylinder that has a lid that has a clamp that when tightened seals the lid to the filter base. There are 2 o rings - one that seats inside the chamber of the cylinder and one that seals the top of the lid to the cylinder base. I hope this helps explain the filter type??
 
The PSI gauge appears to be erratic, normally the pressure is constant at 40 but the pressure gauge girates between 15-40 and after awhile it settles in at 40. This I noticed yesterday during my voyage. As I mentioned the engine will run at idle under load until appr. 1500 rpm and once I attempt to take it higher it will not hold the higher rpm, out of gear it will maintain any rpm.
 
You can rule out the antisiphon valve by shutting off that tank valve and opening the crossover. If the problem disappears, your siphon valve is the problem(or bad gas in that tank). I guess it still could be a clogged vent but that is easily ruled out by opening the fill cap as described by erich.
 
..."Thanks I changed the filters in both cannisters just after the fuel tank, are there others? "

There should be a fine filter after the pump and before (or in) the carb.

Jeff
 
fastjeff I will trace the fuel feed hose to the carb and I should be able to find the additional filter. The other idea I had was hook the other engine fuel line to the problem engine and see if it acts the same. Do you think pouring carb cleaner in the carb to be a good idea?
thanks for your help
 
contender31 said:
sammi I only have one tank in the boat
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Well, that rules out the vent and bad gas! If the line is clogged it is probably at the screen at the carb so changing fuel lines I don't think will help isolate the problem. If you find the screen plugged you might just as well change the other one as the other engine pulls from that tank as well. I didn't know Tiara's had only 1 tank. My 31 has 2.
 
Pouring carb cleaner in the carb is not going to help. If it is the carb, a through cleaning (disassembly) is needed.

Once you rule out fuel flow as being the problem, look around the spark plug wires (when were they changed last?) by the oil pressure sender to see that they are in good shape. Also check that all electrical connections are clean and tight.
 
rich_p said:
Pouring carb cleaner in the carb is not going to help. If it is the carb, a through cleaning (disassembly) is needed.

Once you rule out fuel flow as being the problem, look around the spark plug wires (when were they changed last?) by the oil pressure sender to see that they are in good shape. Also check that all electrical connections are clean and tight.
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Thanks will do, I believe it will lead me there as the engine problems started prior to my changing out the in line fuel filters. I was told to start the engine at night to see if there is any arcing coming from any of the wiring. Dies that work and isolate the wire issues?
 
sammi said:
Well, that rules out the vent and bad gas! If the line is clogged it is probably at the screen at the carb so changing fuel lines I don't think will help isolate the problem. If you find the screen plugged you might just as well change the other one as the other engine pulls from that tank as well. I didn't know Tiara's had only 1 tank. My 31 has 2.
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Thanks will do - yes my 33 foot has 1 large tank - 295 gallon
 
If the carb is a stock Q-jet, the little wire screen is at the fuel-in port. You need to remove the steel fuel feed line and remove the flare fitting. Use flare wrenches.

You likely need a new oil pressure sender, although those push-on connectors at the rear of the guage are suspect also.
 
The fuel pump is on the RH side, down by the forward mount, on the in-line installs.

if you are gonna check the carb's inlet filter, two itmes to note: 1) like Diver_Dave said, use a GOOD flare wrench on the 5/8" nut (You'll need a 1" open end, too) and 2) while the tube is free, it wouldn't hurt to check the fuel pump's pressure delivered to the carb.

You should also check the "sight tube". It runs from the fuel pump to a fitting on the carb, located right above the fuel inlet. The factory provides a translucent yellow Tygon hose that will turn brown and brittle as it ages. This hose should be EMPTY. If it has fuel in it, the fuel pump diaphragm has failed and the entire pump needs to be replaced. If the hose isn't as described above, it, too, should be replaced.
 
sammi said:
Well, that rules out the vent and bad gas! If the line is clogged it is probably at the screen at the carb so changing fuel lines I don't think will help isolate the problem. If you find the screen plugged you might just as well change the other one as the other engine pulls from that tank as well. I didn't know Tiara's had only 1 tank. My 31 has 2.
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Thanks for all your help I will keep you all posted as I go through the procedures you reccommend.
 
Yes but now I have a cooling issue:mad: now i have no water flow and steam out of the port engine exhaust aand I canged the impellers a week ago. Never ending task keeping these old Crusaders working:mad: Time to plant flowers in the engine compartment:confused:
 
fastjeff said:
Good work!

Jeff
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Yes but now I have a cooling issue:mad: now i have no water flow and steam out of the port engine exhaust aand I canged the impellers a week ago. Never ending task keeping these old Crusaders working:mad: Time to plant flowers in the engine compartment:confused:
 
contender31 said:
Yes but now I have a cooling issue:mad: now i have no water flow and steam out of the port engine exhaust aand I canged the impellers a week ago. Never ending task keeping these old Crusaders working:mad: Time to plant flowers in the engine compartment:confused:
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fastjeff said:
Good work!

Jeff
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I think the problem with cooling is the u cooler, i think it is plugged from debris from the old impeller when a fan belt that blew out and overheated the same engine a month ago. Do you know if these can be cleaned manually or do they have to go to a shop to be cleaned? thanks
 
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