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wedge

Malibu VLX Strange throttle and RPM issue - Troubleshooting Direction Requested

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wedge

Bear with me, I am still learning.....

Just de-winterized the boat, replaced fluids before storage, replaced raw water pump impeller.  Put about 3 hours on it, and it was running fine.  Now the highest rpm I can get is at about the 12 o'clock mark on the throttle, any farther than that, RPMs dip.  If I return to 12 o'clock, rpms go back up.  The engine idles and starts fine, which most of the posts I have read either idle rough, or cap out at an rpm.  Besides this issue engine sounds fine for 15 years old.  I have added 12 or so gallons of fresh fuel to the boat.  I would like to avoid taking it to the mechanic, any suggestions for what I can look at to identify the problem?

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RTS

What RPM are you showing before it starts to dip?

 

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wedge

I can check that tomorrow, when it was happening I didn't think to note that when it was happening.  I'll add it when I test tomorrow.  A friend of mine suggested limp mode too.  I have a little leak in the raw water pump, thought it wasn't a big deal.  

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oldjeep

I assume it has a mechanical throttle cable - have you checked what is happening at the throttle body when the throttle moves past 12:00 ?

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wedge

Yes it is a mechanical throttle.  No but that is exactly the kind of help I'm looking for.  I will get the RPM level and see if the throttle body is opening up when I go past 12 o clock and post my findings tomorrow.  Any opinions on the leak in the water pump?  I'm thinking ill just replace anyway, but want to identify this issue as well.  Any way to tell if the engine really is in limp mode?

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ski40mph

This time of year in cold states we get condensation in the gas. I always have to empty/change my water separating fuel filter. Where are you?

If you can get it on plane, check to see if waters coming out the exhaust. If it is, I wouldn't worry about the raw pump leak for now.

Indmar engine? Raw water pump on the crank?

 

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ski40mph

How much gas was in the tank when you winterized?

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Bozboat

it could be old gas

it could be a fuel pressure problem

it could be time to have the fuel injectors cleaned

The cap and rotor may need changing.

Get a fuel pressure gauge on it and see what that says at key up, at idle, and at WOT (may not be possible)

From Bakes Resource Page:  Pressure at Key-up 43-45, PSI Idle 35-38 PSI, WOT 43-45 PSI

Edited by Bozboat

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minnmarker
46 minutes ago, wedge said:

Yes it is a mechanical throttle.  No but that is exactly the kind of help I'm looking for.  I will get the RPM level and see if the throttle body is opening up when I go past 12 o clock and post my findings tomorrow.  Any opinions on the leak in the water pump?  I'm thinking ill just replace anyway, but want to identify this issue as well.  Any way to tell if the engine really is in limp mode?

I think OJ was suggesting you take the flame arrestor off and, with the engine off, look at the butterfly valve in the intake to see if it moves to full open when the throttle is pushed all the way forward.

If that all looks OK then you probably have a fuel supply issue.

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wedge

To add to that too, my buddy said he thought the fuel pump sounded loud.  It wasn't any different than last year that I could tell, but he had the exact same boat a few years ago.  I really appreciate the help here.  Quick question, for gas is it better to add more gas, or run this gas out until its almost empty?  I've got a buddy with every tool under the sun, I will check fuel pressure tomorrow too.  How can I check fuel injectors?  Also, how do I know when the cap and rotor need changing?  For the last 2 there, I haven't done any research on what those are yet.  

 

 I really appreciate the help here, and I will report back tomorrow night.

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Bozboat
Just now, wedge said:

To add to that too, my buddy said he thought the fuel pump sounded loud.  It wasn't any different than last year that I could tell, but he had the exact same boat a few years ago.  I really appreciate the help here.  Quick question, for gas is it better to add more gas, or run this gas out until its almost empty?  I've got a buddy with every tool under the sun, I will check fuel pressure tomorrow too.  How can I check fuel injectors?  Also, how do I know when the cap and rotor need changing?  For the last 2 there, I haven't done any research on what those are yet.  

 

 I really appreciate the help here, and I will report back tomorrow night.

Take a screwdriver and release the two screws on the rotor, look inside the cap.  If the contact points look corroded, (similar to battery corrosion) replace the cap.  be careful not to get the wires out of order.   The rotor will be on the distributor, replace if it looks corroded.

Next, I would check the fuel pressure. The results will help decide what next to do.   You may also need to replace the fuel filters and use a Q tip to wipe out the screen on the bottom of the fuel pump.

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wedge

I freaking love this site!  Definitely buying a T-shirt to support the cause.  I've never seen an online community so helpful.

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wedge

Just to close the loop on this one.  It was either the cap and rotor or the fuel filter.  Replaced both before I bought a new fuel pump, that did the trick.  At a recommendation from a friend, i left a quarter tank of gas instead of 3/4, I think that fouled up the filter as it was pushing enough gas through before.  Thank you everyone for your help!

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