Crusader 6.0 L Losing Power Under Load

I have been having this issue for about two weeks now. The boat is a Pursuit Express with two 6.0 L Crusaders. While under way the starboard engine begins to lose RPMs (couple hundred to several hundred rpms) while the port engine runs fine. This first showed when running at high rpms (3000 or so) and pulling the throttle back to under 1500 rpms and it seemed ok. Replaced the plugs, but the problem still is there. Just had the boat out this afternoon and now the problem is occurring under 1500 rpms.

If I take the engine out of gear and run the rpms up to over 2000, everything seems ok. So it is under load that the problem shows itself.

I will change the fuel filter, but I am not sure that is the cause of the problem since it runs fine when out of gear.

If you have any ideas, I would really appreciate it.

Thanks for any help.

Jim W.

Sounds like a possible fuel issue. Do you have separate tanks for each engine? If so do you have valves to run both engines on the port tank? Could be bad gas in the starboard tank or a clogged vent line. Try it with the fill cap removed. Check/clean the anti-siphon valve.

Thanks Erich. There are separate tanks, and no easy way to run both engines from one tank. Always fuel both tanks at the same marina so bad gas in the starboard tank probably not the cause, but I can't rule it out completely. I like the idea of running with the fuel cap removed, I will give it a try. Not sure I have an anti-syphon valve, I will research that. Thanks again!

jim,

I believe all boats with gasoline engines are required to have anti-siphon valves. They are usually located at the top of the pickup tube just before the fuel line to the engine or filter or whatever is downstream. They have a spring loaded SS ball that prevents fuel from siphoning into the bilge in case of a fuel line break/leak somewhere that is lower than the level of the fuel in the tank. Check those fuel filters and or separators. The amount of fuel required in gear is more than in neutral so the "at the dock" test doesn't really mean much.

Erich

Erich sent you down a viable path...

I would add checking the o-ring on the fill port's cap to make sure it isn't cracked. The other item you need to get is a fuel pressure gauge. You need to check the fuel pressure under load, at cruise and WOT. If the pump isn't making adequate pressure, the injectors can't deliver the appropriate amount of fuel and you will experience the loss of rpm/loss of power syndrome.

And another thought. There may be air getting sucked into the fuel line somewhere through a very small leak in a fitting or hose that is not big enough to leak fuel but does allow air to get sucked in. A possible test is to temporarily replace the fuel line from the tank to the engine.

First, thanks everyone for your help. Today, I ran the boat and the loss of power only happened a couple of times (fixing itself , but I doubt it). What I did do, is to fuel up the boat and checked the vent while fueling. Put my hand over the vent port and could feel and hear the vent working properly, so the vent is not stopped up.


I put a new O-ring on the gas cap and tightened it down securely. It did stumble slightly after doing this but then I removed the cap completely and the engine seemed to run fine even with the cap removed.


Next on the list is to replace the filter and see what happens. I do have anti-syphon valves on the tanks and I will replace them. I am beginning to suspect the the anti-syphon valve. Maybe got gunked up with lack of off season use, and now clearing itself with more use now??


I will keep you all posted. Again, thanks for the help.


Jim W.

I believe that you have an injected engine with a MEFI controller. (If not ignore the following....) All of the suggestions you have heard are sound, but what you should first do if determine the model of you controller (likely an MEFI 4) and get a diagnostic manual for it. If you look they are available for free on the internet. You will find over 300 pages (print double sided!) of invaluable information on how your engines work, along with diagnostic procedures on most problems, including yours.

Since, as you have been advised, fuel starvation is the most likely candidate, you start with the filters, which is always a good thing to do anyway. If that change does not cure it, you should next check fuel pressure, underway, to see if it falls off when the problem occurs. The manual will give you the correct pressures. The best (cheapest) source for a gauge is to borrow one from a friendly auto parts store that has tools for loan or rent. Failing that, buy a cheap one at Harbor Freight or on the net. I got a $30 one at Harbor Freight, on sale for $10. Of course the actual gauge part leaked gasoline (cheap tools are not always any good) so I had to buy, for $10, a good quality 0-100psi head that is readily available. Since the rest of the kit is just a hose with a female Schraeder valve connector (larger than the one on a tire gauge) another possibility is to go to a shop that fixes air conditioners and get a hose and fitting used to fill them with refrigerant. That fitting is the correct size.

If your tests show falling pressure when the issue occurs, then you can focus on that. Start with the easy stuff (anti-syphon valve) and move on the the hard stuff (fuel pumps). Another thing that is a possibility is some clogged injectors. They really should be pulled and sent out for testing and cleaning every few years, unless you boat is operated four seasons. They crud up if not used. Cost of bench testing and ultrasonic cleaning is around $10 to $15 each. And keep in mind that if it is fuel starvation, lean engines run hot and burnt valves can happen if you do prolonged running in this condition.

If you have good fuel pressure, and your injectors are flowing to spec, then you need to move on to the many other possibilities you will find in the manual. Most of them require a scanner (must be marine, automotive types will not work) so unless you borrow or buy one you will need to find a competent, well equipped engine mechanic.

Good Luck.

Just a couple of other thoughts. PM me if you cannot find the diagnostic manual. It is really essential. You said you were going to replace the (fuel) filter. There should be two filters, the replaceable one and an earlier one somewhere in the system that is to be cleaned, not replaced. Also do not forget the best diagnostic tool we have with twin engines, that is part swapping. If your pressure tests show a falloff you can always swap the fuel pumps (one at a time) and see if the problem moves. If it is not fuel pressure and you do not have access to a scanner you can swap some other suspects such as the manifold air pressure (MAP) sensor, or the crankshaft position sensor (if your manual says you have one). If erratic they could cause your problem and they are a quick swap. Finally, you should pull the distributer cap and inspect carefully for corrosion. That could cause your problem.

Good Luck.

New fuel filters solved the problem.
Thanks for all the help.

Such a simple fix for what seemed like a more complex problem. Glad to hear all is well again.