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95 response help needed

Malibu newbie

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I have the mrecruiser 265 HP EFI motor. Just bought the boat a month ago after it had set up for almost 4 years. took it out the first time and it wouldnt hold steady rpms...you could gun it and it would come out of the whole good but once it got up to speed it would fall off about 1k rpms, you could bring the throttle back and feel the motor pick back up. changed the cap, rotor and plugs (the cap was really corroded) thought that would fix my grimlin but when I took it out this past Sat. did about the same thing.

Between the three times I have taken it out, I have run almost a full tank of supreme throught it along with a can of Seafoam. at the end of the day Sat i could get a steady 3200 rpms at about 36 mph and it would hold that at full throttle, but i know the boat should run faster and higher rpms than that. I am starting to think it may be a fuel delivery problem...maybe pressure related. But I am open to all suggestions. The boat starts fine, idles fine and runs mid throttle fine.

Thanks in advance

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Could be lots of things, but it would be good & inexpensive to change out the fuel filter(s). That engine/boat combo should top out in the mid to upper 40s & turn 4400-4800 RPM.

It could also be a prop issue in that you're over propped - making the problem worse.

What prop is on the boat now? It should be stamped on the hub of the prop.

Previous owner could have changed it out to lower the RPMs at a certain speed to attempt to help with fuel consumption.

Start with the fuel filter(s) & let us know about the prop.

Edit - clarified.

Edited by wienrdog
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Sounds like the fuel filter. I had a similar problem and a new filter fixed it.


it has a new seperator filter on it...will get the numbers off the prop in a few and post back

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Do you have access to a fuel pressure gauge? Would be nice to see what that is doing.

How does the motor idle?

If that pans out then you move onto the sensors, TPS, MAP, and IAC.


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These guys are all pointing in the right direction. I have the same motor and similar issues last season / end of the prior season. Mine ended up being the pump itself, sparatic pressure. Long story short, it was none of the cheap fixes (Filters, bad gas, plugs/wires/cap) I tried prior to biting the bullet on a new pump. The reaction of the boat to throttle is 100% identical to what I delt with. Out of the hole, the boat was still an animal. Once on plane the boat would lose RPM from 3/4 to full almost bogging (too much air), pull back on the throttle and boat would pick up again to about 3600 RPMs. This motor should run around 4900.

Just curious but wouldn't the prop be a constant problem? Bog throughout the enotre RPM range? Not race to speed and drop off?

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ok guys..prop says 13X13L also stamped is "mr Minus by Dymex" guess I will try the fuel pressure thing today and go from there.

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3200 rpms at about 36 mph- That sounds off. You may want to check your speedo because in that boat with a 13x13 non CNC prop you should be close to equal RPM's and speed.

36MPH around 3450 - 3600 RPM's

But that's not your root issue.

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The prop should be right for the boat & it would be a constant problem. 36MPH @ 3200 RPM seemed off. An over prop would make the situation seem worse.

You sure that separator filter is the only filter in the line? There is usually a silver canister in-line filter just off the gas tank. Perhaps the previous owner replaced it with the separator filter.

Did you check the screen on the inlet side of the fuel pump (another location where there may be debris accumulated).

Best to rule out the less expensive problems before replacing the pricey fuel pump.

The schrader valve should be after the fuel pump or on one of the injection rails. (But I'm not sure where on that engine).

Edit - clarification.

Edited by wienrdog
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the first trip out I figured there was water in the gas and it needed to be run. I only had about 1/8 of a tank of the original gas left in the tank that I couldn't get out. but even with almost a full tank of super, a can of seafoam (which is supposed to let the water burn) and new plugs, cap and rotor, the problem still persists...it is definitly better than the first outing, but still there. I traced the fuel lines from the tank forward and it seems the only filter is the one at the fuel pump assembly that is a filter/seperator.

The only other thing I didn't mention is when I first got the boat, it wouldn't run unless you sprayed carb cleaner in the trottle body. I found out that on top of the tank there is a 90 with a check ball in it. When we went to remove the fitting it broke and realized that the ball was stuck. I replaced it witha fitting I had lying around that was the same size without a checkball in it.I spoke ot a guy that works at a Malibu dealership and he said dont worry about the check ball.

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Sometimes a fuel pump can troubleshot on the fly with fuel tank fill levels. If it runs better full v. empty, that is an indicator of a problem with the pump. More effective on a carbed engine though.

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The prop should be right for the boat & it would be a constant problem.

You sure that separator filter is the only filter in the line?

Best to rule out the less expensive problems before replacing the pricey fuel pump.

I agree 13 x 13 should be stock prop.

My setup (same motor) had no filter (just seperator) stock from factory.

I wouldn't jump to spending the money on a new fuel pump, but I would stop looking for a the cheap fixes and get the pressure checked! Wasted a lot of last summer on narrowing the cheap fixes out of the equation. Also spent more then the fuel pump would have been with replacing minor parts.

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working on getting pressure guage hooked up, I have yet to find a schrader valve so it looks like I will be plumbing an inlet in. it looks like it will be raining for the rest of the week here, so should have plenty of time to get the guage hooked in and maybe know something later in the week.

Thanks everyone for your help..I dont mind changing little things...at least I know they have been done :)

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Ok, here's a wild one for you: Run the boat with the gas cap off and see if anything changes. If so, you have a problem with your gas tank vent line.

I have read many places, but don't see mentioned here, something about a screen in the fuel line at the pump. Maybe pull the connection there, see if there is a screen, and clean it up if clogged.

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ok guys...will have to get a fitting for the fuel rail to use the fuel pressure guage, I will try to do it today if I can get away from work. we tested the TPS last night and it has almost 5v at idle then at WOT it drops to .69v, this seems backwards from every car I have messed with. Now I realize marine stuff is different, but is this the right reading for the sensor? Also, didn't find any screens in the fuel pressure lines coming out of the pump or into the TB.

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Not sure from your statement if you looked at all the fuel connections or just from lines from the fuel pump to the TB...

The screen we were talking about is in the fuel pump inlet where the low pressure line from the tank attaches to the pump. It's not in the line, but part of the pump.

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i pulled the connections from the lift pump into the electric pump and didn't see a screen, then checked from the pump to the tb and still no screen (didnt expect it to be there)

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Update: I went to the river yesterday (Sun) and fuel pressure was rock solid at 30 lbs even when the boat stumbled. I changed the coil while there, and boat acted the same. I even undid the fuel cap and no change. once back on the trailer, we went by the auto parts store to check on the plug wires i ordered and had the ignition module checked and it failed. So, I bought a new one and replaced it. I will try it again this afternoon if I get off in time...fingers are crossed :)

Sorry guys...had this in the wrong section.

Edited by Malibu newbie
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  • 2 weeks later...

well here is an update incase anyone experiences the same probs. I pulled the boat all the way to Austin to Ace Marine on lake Austin. It was worth the whole 3 hour trip!! the guys there are Awesome! finally found a nicked wire that feeds the PCM power and they rebuilt the throttle body and cleaned the injectors and presto....4500 RPM's all day :) the boat idles better and doesn't stumble when placed into gear. If anyone is in the Austin area and needs quality work done, I highly recommend these guys. Thanks for all the help.

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