Only 2400 rpm max under wot and load

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searayjay

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2001 Searay 240 5.0L mpi.only 250 hrs
Ran fine last weekend, this weekend, starts and idles fine but will only pull to 2400 rpm under load and a little rough running. 40 psi oil press, temp fine and volts normal as well.
I guess I will try new fuel filter or any other suspects?
Thanks
 
fuel filter and junk on the prop

any backfire at WOT?
 
Any recent work been done on it? Even recent "checking" on things? Low power and running lumpy, sounds like a spark plug wire off, or a couple cylinders reversed. 1-8-4-3-6-5-7-2 Carefully trace the firing order and be sure they're all on the right connections, and tight.
 
No recent work but I will check plugs and change fuel filter. Nothing on prop
 
I'd check cap & rotor for corrosion and scan the ignition to check for possible knock-related timing retard due to degraded fuel.

The marine scan device should also allow you to perform a "power balance test" by either shutting down 1 injector or 1 ignition spark pulse at a time sequentially so you can see if that does or does not reduce rpm by approx 1/8 . If it does not reduce rpm, that cylinder is likely not combusting, and it could be evident for more than 1 cylinder.

Scan device will also confirm the TPS position value is reaching 100%.

An inductive timing light with pickup attached to one plug wire after another would show which cylinders are getting ignition pulse from the distributor.

A fuel pressure gauge attached to the fuel rail Schrader valve will determine whether the pumps are supplying full proper pressure. If not there could also be a restriction upstream.
[FWIW- the fuel pressure spec for 2003 Crusader 5.0 L and 5.7 L MPI engines' HP pump output is 57-62 psi at W.O.T. ( & LP pump output spec all rpm is 4-7 psi. .) ]
 
Sound like shift interrupt switch loose it ground connection for ignition timing. Check continuity across terminals of shift interrupt switch and make sure you got a good reading when in neutral. For under $50, I'd just replace one if you don't find anything wrong on your engine.
 
quote:
Originally posted by DeeVee

Sound like shift interrupt switch loose it ground connection for ignition timing. Check continuity across terminals of shift interrupt switch and make sure you got a good reading when in neutral. For under $50, I'd just replace one if you don't find anything wrong on your engine.

Click to expand...


Good advice, but be careful at the parts counter. At least on earlier models, the Carbureted versions provided Ground by CLOSING the Interrupt Switch. All eight cylinders missed. But the EFI ones, with a PCM, OPENED a circuit and caused four cylinders to drop out.

MerC re-designed their Shift Plate when their microswitch supplier quit supplying. Went from a lever-looking switch to one that's more of a push-button. The new plates were sold marked "Carb" and "EFI" because they were shipped with the appropriate switch attached. Plates themselves are the same. I have one if somebody needs it, with the EFI version of the switch.

EDIT: Thinking about how the EFI engine drops cylinders to shift out of gear, I wonder WHICH cylinders... If it's FOUR, like I believe to be true, and those Four are every other one in the firing order, enough engine torque would be dropped to let it out of gear, but the engine'd be relatively smooth. Probably over thinking, just wondering...

More Overthinking... EFI engine could run on Four... So "What If" something is sticking and Shift Plate isn't staying in "Normal?" That Shift Plate should put Interrupt Switch out of it's "notch" when you come OUT of Gear, with the propeller UNDER LOAD. Should never move, coming OUT of Neutral into Forward or Reverse. Should never move on ANY shifting if the Prop isn't in Water providing a load on the Lower Shift Cable. Should move ONLY coming OUT of Fwd or OUT of Rev, IN the water.
 
Update, changed fuel filter and plugs, wires, rotor and cap were changed a couple yrs ago but only 20hrs of running. Shift interrupt seems to be working mechanically.
One more thing I recall, the seemed to jump up a few times(without engine rpm changing) after I pull ed back to idle or when out of gear and simpky revving engine. Since vibrating/ rough running under load and rpm only reaching 2400(about 1/2 of loaded redline) this seems to me to be electrical- tps or ecm or ignition sensor?
Just grasping?
 
I'm still thinking you have a shift interrupt switch problem, you can connect a two long jumper wires and ground them together when it's happens and see how the rpm reacts to it.
 
Given Deevee's suggestion and j-d's description of the interrupt system and the fact max attainable RPM are just under 1/2 of the spec for that engine , that certainly does bear looking into.
 
Ok, I'm going jumper the interrupt switch and splash it and see what happens and hope it is that simple!!
Thanks everyone
 
Could still be fuel or electrical. Try the separate fuel supply. Check fuel lines for loose connections or cracked fuel lines. Not enuff fuel getting in causes a lean condition and can backfire thru the carb.

If electrical, check all primary electrical connections...like coil connections and distributor plug connectors as well as connectors to ECM. Check distributor. make sure the toothy thingy passes evenly between the pick-ups. Make sure it's down and the 'teeth' aren't bent. when they stamp out the toothy things, sometimes it leaves a flake that may become loose.
 
Well, all looks good but haven't taken it to river. But I had a few questions. I checked codes and no stored faults, just beeps out a "12" which Im told is just reset. Also if guardian mode, why do I get no alarms? Other than the normal 2 beeps when you originally turn on ignition
 
I can't help with the codes, just wanted to mention that if you jumper the Interrupt Switch, and that gets the engine "hittin'on all eight" you probably will NOT be able to maneuver, shifting In/Out of Forward/Reverse. The engine's torque will keep the "undercut" shifter dog from releasing, and if you DO manage to get it out of one gear, it's likely to fly out of one gear all the way to the other. Pull out of Fwd, wind up in Rev, or vice versa.
 
I thought I knew where the shift interrupt switch was but there is no switch there. The plate is attached to port riser with 2 shift but no electrical wires. All the internet pics show what I have but I see no elect switch.
Also 4 plugs looked good and 4 looked covered with oil/gas slightly.
So I think something is cutting out spark on 4 cylinders like what is described by shift interrupt
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Uh... Er... An... Ok... Which Drive do you have? Only Alpha Drive has a Shift Interrupt. Any Bravo, B1, B2, B3... does NOT.
 
I remember seeing a number of the smaller Sea Ray's with B3. By that I mean the 21EC's like ours, and the smaller Sun Dancer's. Didn't think about it and you said "prop" not "props." This is sounding to me now, like you need a full scanner along with a fuel pressure tester.

Always remember, NEW parts can still GO or BE BAD.
 
Thanks j-d. I think you are right.
I need professional help and tools- computer scan and fuel press.
Thx
 
my bad, sorry. Shoulda ask for more info before jump in with.
 
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