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8.1L falls off at 3000 RPM?

D

Dockholiday

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I have a 2005 Silverton 340 w/ twin 8.1L crusader 496 engines. They have fresh spark plugs, new fuel filters (but not the little inline ones) and low hours. Stbd engine falls off at about 3,000 rpm. It is strong up to this point w/ both throttles about equal to one another as you run it up. Then the port motor keeps going and the stbd acts like it won't take more fuel. It is not loading up and smoking, I can't tell that it is missing either. It acts like the throttle just stops advancing - very strange. Then after you run for a while during the day, it might take off and run perfectly. I have no idea what could be causing this issue. I just installed new plugs and nothing changed. Has anyone ever had an issue w/ these engines like this? Could it be something w/ a bad fuel injector? I get no check engine lights at the dash either. Thanks.
 
it is likely to be fuel starved...vent for the tank (if separate tank for each engine) could be clogged, anti-syphon valve could be clogged, or the screen on the bottom of the pickup tube is getting covered with crud.
 
I was afraid fuel starvation could be the issue. There is a very small inline screen right at the block which is hard plumbed in to the fuel system. I did not replace this screen because of the difficulty it presents to dismantle. If I don't get any other possible scenarios, I'm going to have to figure out how to take all of it apart so that I can service this filter. Thanks for the comment.
 
probably unscrews...too many different variations without looking. could also be a pump issue.

I'd get a fuel pressure gauge hooked up for a start. You need to see what happens to the pressure in the rail, under load, at the higher RPMs.
 
Had a similar issue with my 8.2 MPI engines, it has a "pancake" screen fuel filter before the Racor filter. The screen was totally clogged with crud, I could only get about 2500 rpm from the engine. Cleaned up the screen and that was the end of the problem.
 
I bet that is it. Same configuration and the screen filter is just ahead of the Racor. Looks like I'll tackle that dude and keep my fingers crossed. Again, thanks for the help from everyone. I know what must be done now - if it works i'll let you know.
 
Are you sure the secondaries are opening? Pull off the flame arrester and look down the carb with it running wide open (with someone else running the boat of course) they may be binding.
 
Have someone add a bit of choke with the external linkage when this happens, If the motor picks up, then falls on it's face, you have a fuel starvation problem. If it doesn't do a thing, start looking at ignition problems (wires, coil, etc.)

Jeff
 
Yes, I should do the pressure gauge on the rail. I have one filter that I would bet is the culprit though. I'm going to have to figure out how to change it sooner or later - the plan is to start with that first. Then if that does not fix it I'll pressure check to be sure it's not a fuel problem. The boat is 7 years old, so the filter needs to be changed.
 
It's "Doh!" but you're right: I missed that.

Be careful if it's fuel stavation; you could burn a piston. Also, seeing that a MPFI setup, one dead injector could lean out a cylinder and cause your lack of power. That would show on the plugs, however, which would simplify your troubleshooting ordeal.

Jeff
 
If you have the same kind of "pancake" arrangement it looks alot more intimidating than it really is to clean. Hence why I went three years without doing anything to them and then had the starvation issue occur. Again if the same as mine, there is a single bolt in the center, shut off the fuel line at the tank, get some rags, or container to catch the small amount of gas that will come out, take the bolt out and then pull apart, the screen can the be removed, cleaned and put back, bolt back together, make sure gasket is seated correctly and that's it. Dont have to remove any fuel lines or anything. Takes about 10 minutes once you do it. Of course on my engines the port side takes longer because the filter sits outboard and it takes some yoga moves to get to it.
 
I hope mine is that easy, sure messed w my head when I looked at it before. I do have the same port side issue as well. That should be interesting.
 
Also, depending on which version of the 8.1 you've got, there may be a "fuel cell." Mine in forward starboard. It contains pumps and a paper element fuel filter.

Also, the suggestion about a fuel pressure gauge is good. it's easy. There is a port for it already plumbed. Get the specs. If, under load, its not reading what it should, you've got a fuel delivery problem prior to the high pressure rail.

Good luck,
Bruce Clarkson
 
I've been chasing a similar issue for two years. Can come up on plane once, but if I have to come down for any reason, I'll never get back on plane. When I try to get back on plane, at ~2200 RPM (about the time the second injector kicks in on the 454 XLi), the port engine falls over. I tap the throttle down and she catches up and goes back to 2000 RPMs. After multiple tries, she falls over at ~2200 every time. But if I shut her down for an hour or so, she'll do fine until I try to come up on plane a second time after the rest. It was this sporadic running that had me scratching my head; how could it be a fuel issue if it always works once. Last year I never ran fast and it was therefore never an issue, but this year I've had to run fast a few times and the problem is still there. My mechanic informed me that before I spend hundreds if not "B.O.A.T" dollars with them, try the 115 micron pancake filter. Damn if it didn't work. Crazy puzzle is finally solved. He also said that Crusader does not even use the 85 micron filter any more. I clean the filter at least twice a year, and could see through it, but I guess it wasn't enough. Could also be the pump is old and worn as she has 1025 hours on her.
 
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Yes, I have the fuel cells, I've replaced the o-rings and paper element on both engines, still the same issue. That is why I need to get the primary filter ahead of the fuel cells 'right' - then there will be no excuses. I do need to hook up the gauge on the fuel rail, I'm sure that tells a story. The primary has never been changed and it needs some attention, so I'm still focused on that as priority one. I'm out for a couple weeks, so I still have not had the time to change it to see if this is the fix or not. Many Thanks.
 
This is a picture of my dilema. The pre filter is to the far right - as you see, there is a street L coming out of the filter housing, then a valve, then the hose w/ fitting from the tank (incoming fuel). It looks to me like the hose will have to come off in front of the valve (lot of good the valve does) then screw out the valve body and fittings from the street L before I can unscrew this filter housing to install the new element. Is this the only way to do it?

IMG-20120613-00071.jpg
 
That was likely the doing of the riggers at Silverton that did the install....definitily done without much thought to maitainance if the pieces are as you described. can't tell from the pic exact choice of the fittings used. you may be able to loosen the fitting on the end of the hose and remove everything "upstream" of the 90 EL at the prefilter's inlet. Better to byte the bullet now and get it right that defer it until the next time...so much easier to fix anything in the slip than miles from home with the thunderstorm bearing down on you.
 
What is a Schrader valve? Is that the anti-siphon valve? I'm hoping when I take all this apart that the thing will work and not try to keep pulling fuel? It's going to be messy, but I will have a way to plug if off when I disconnect.
 
It's a small test fitting that resembles an auto tire stem (where the air goes into a tire). Usually there's a cap over the end for safety and to keep dirt out. Every EFI engine I've seen has one somewhere.

Jeff
 
I have an MPI, the schrader valve is on the fuel rail on the opposite side that the regulator is on, on my engines it is on the left side when facing the front of the engine, look under the intake manifold. It is about mid point on the rail and is covered by a small cap.
 
I have an 89 phoenix 27' with 5.7 crusaders. port side makes it to 3000 and strains to go anymore.no smoke, no miss,starts fine, idles well. I put a carb kit in it. no change. This thread has been very helpful. Thanks.
 
The problem is fixed! Primary filter on both engines very dirty and clogged. I will post pics of the fix later. Added a couple unions to the plumbing so that the filters can be changed easier in the future.
 
Here is my attempt at correcting the plumbing issue I was experiencing (see photo above and compare to this pic). Now that I have re plumbed and added a brass union, I will be able to close the valve, break the union, and unscrew the filter body to install a new cartridge. BTW, the filter had never been replaced on either engine and now everything runs fine. My only concern is the brass union that I installed into the system - hopefully this is a 'safe' way to remedy the issue. I did this configuration on both engines. Thanks for the help in getting this situation corrected.

IMG-20120630-00102.jpg
 
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