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2012 VTX Engine Problems


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New member to the crew here and first time boat owner here, looking for some general guidance and wanting to learn as much about my boat as possible. Just bought a used 2012 Malibu VTX. 350 Monsoon with 360 hrs.

 

Thus far, it ran great for the first 2-3 weeks. But then suddenly started having engine troubles (be prepared for a lengthy post here…) The first time it happened, I could feel little surges when moving at idle speed. As soon as I tried to accelerate, the boat started shaking so violently that I didn’t even try to get it faster than about 8mph before backing off the throttle. I then shut it off to check if something was wrapped around the prop, etc. Nothing was there and by the time I got back into the boat and started it up, the boat turned started normally and began running nice and smoothly for the rest of the day.

 

Fast forward 3 weeks (had to get the trailer repaired due to a melted bearing…) I finally got a chance to drop it back in the lake. It started up smooth. However, as soon as I throttled up, I could tell the engine wasn’t running properly. Sounded like a sort of mistimed chugging sound (misfiring?). I’ve had several people recommend putting some seafoam in the gas to perhaps clean out whatever may be sitting in the tank/injectors/etc. Turned the boat back on and the boat barely started. I let it idle a bit to warm up before pulling away from the dock. To my dismay, when I throttled up, the engine sputtered and then stalled. It took two additional sputtering and stalling cycles to get back to the dock before taking it out of the water to living to float another day.

 

Incidentally, the k&n filter looks like it’s kind of crushed a bit against the backseat back (to the point that the metal cap on the end of it is partially popped off). I don’t know if it’s related to the problem, but definitely seems like it should be replaced since it’s appears damaged. Anyone know the correct part that will fit in that space?

 

There aren’t any active alerts showing on the maliview screens, so I’m left guessing. I’m certainly not opposed to taking it into a dealer to get it repaired, just hoping to avoid the rest of the season being shot if it’s something that my mechanically inclined friend might be able to assist me with repairing. 

 

Any words of wisdom welcome, even if it’s just saying “yeah… take it to a qualified mechanic”

 

Thanks for the help in advance!

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Unless the spark plugs look brand new, I would start with a full tune up.  It sounds like you probably have a spark misfire, so a new cap and rotor, plugs, and even new plug wires may help a lot.  Since the boat is new to you, starting out with new expendable parts puts you in a position to know what you have and how old the parts are.

It might also be worth your time to get a can of carb cleaner (catalyst compatible) and clean the inside of the throttle body.  It might be a pain to get to it so you can see what you are doing, but the edge of the butterfly and the side orifices should all be clean.  Open the throttle to make sure you can get down the throat and along the walls.

If these two things don't fix it, come back and we'll try to help some more.

Welcome to the crew!

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Fuel quality is at the top of the list however Sea Foam will not fix any fuel problem you may have and can make it worse, if it does anything at all.

Do you have a fuel pressure gauge?

https://www.harborfreight.com/basic-fuel-injection-service-kit-64939.html

 

You can do a couple things with this. Get a fuel sample from the fuel rail into a clear container and let it sit. Any water at the bottom?  How does the fuel smell?  Is the fuel system holding pressure when it’s miss firing?

I agree with Gary that it’s probable due for a tune up unless you have proof the PO had it done.  Use the proper Champion plugs.  Use a distributor cap with brass contacts, not aluminum.  I’d hold off on the wires until you can prove you have a bad one. They almost never fail these days. 

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4 minutes ago, robtr8 said:

They almost never fail these days. 

Hard fail, true.  But they do gain resistance as they age, making the spark weaker.  If the OP's wires are nine years old, it is time to consider a change.  I didn't hesitate to change mine when I bought my used boat.  It had a slight miss at idle that cleaned up nicely with a full tune up and throttle body cleaning.

Diagnosing issues without fresh expendables and a clean intake can be very frustrating and expensive.

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Thank you for the ideas to start with! The dealership I bought the boat from said they had changed the oil and plugs, but I’m thinking I need to check the plugs myself just to be confident. (I’ll also be contacting them tomorrow to find out exactly what they did when they “tuned it up”. 
 

Either way, sounds like I have a busy boat maintenance week ahead of me with performing the suggested maintenances and running tests in addition to cleaning out the oily residue and grime from the bilge and around the engine itself. It keeps looking like an oil slick coming out of my bilge when it pumps out the rainwater. 

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3 hours ago, robtr8 said:

Fuel quality is at the top of the list however Sea Foam will not fix any fuel problem you may have and can make it worse, if it does anything at all.

 

18 minutes ago, SpartanVTX said:

It keeps looking like an oil slick coming out of my bilge when it pumps out the rainwater. 

I was going to ask where the boat is stored, but it seems you kind of answered it for me.  In addition to the tune up advice, I would put a few bottles of Heet in there just in case there is water in your fuel.

28202-iso-heet-enhanced-750x500-min.png

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So far, the weather has really only allowed me the time to check the spark plugs, which look to be brand new. However, the one thing I noticed is that the it looks like I would need to take the plenum off in order to get to the distributor cap and rotor. I see there are 6 bolts on the top. Is there anything I should be careful of when removing that to get to the cap/rotor? Any gaskets I need to be prepared to replace, etc?

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On 8/22/2021 at 10:56 AM, robtr8 said:

 Use the proper Champion plugs.  Use a distributor cap with brass contacts, not aluminum.  I’d hold off on the wires until you can prove you have a bad one. They almost never fail these days. 

Champion?  The manual calls for AC Iridium (41-101) 

Edited by oldjeep
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9 hours ago, SpartanVTX said:

So far, the weather has really only allowed me the time to check the spark plugs, which look to be brand new. However, the one thing I noticed is that the it looks like I would need to take the plenum off in order to get to the distributor cap and rotor. I see there are 6 bolts on the top. Is there anything I should be careful of when removing that to get to the cap/rotor? Any gaskets I need to be prepared to replace, etc?

Yes - you have to take those 6 bolts off to tilt the plenum out of the way - easier if you disconnect the harness at the throttle body, then you can remove it completely.  You should not need to replace the gasket it comes off clean and reseals.  I've had to do this a couple times on my 2012 VTX.

The distributor cap would be my first bet.  The pylon drains right onto it and the contacts inside get really corroded if you still have the stock type cap with aluminum contacts.

I replaced my cap rotor with brass contact Accell stuff

cap - 120141

rotor - 130141

WP_20160610_16_46_47_Pro.jpg.d98920125c44c7e5d7e4454c560975e8.jpg

Edited by oldjeep
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Should also mention since you have a 2012 VTX.  If you ever start getting random misfire codes - talk to your dealer about getting the ECM software updated.  There is a misfire calibration for the 2012-? engines that takes care of some overly sensitive misfire detection.  Drove me crazy for years chasing it.

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3 hours ago, oldjeep said:

Champion?  The manual calls for AC Iridium (41-101) 

Yes, AC Delco, sorry.  Just not NGK’s.

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2 hours ago, oldjeep said:

Yes - you have to take those 6 bolts off to tilt the plenum out of the way - easier if you disconnect the harness at the throttle body, then you can remove it completely.  You should not need to replace the gasket it comes off clean and reseals.  I've had to do this a couple times on my 2012 VTX.

Thanks for this! I’ll admit that I’m a total novice on these things (trying to learn as much as I can without causing myself more problems haha).  I understand the general concepts, but well aware of when I’m into an area I don’t understand yet! I wouldn’t even know where to begin to look if I screw up the gasket and need to replace it. 
 

I just ordered the cap and rotor to have on hand when I ultimately pull the plenum off to check things.
 

Incidentally, the flame arrestor looks to be kind of jammed in there as well, maybe it’s not actually the correct one? (Trying to figure out how to post a picture of that now…)

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2 minutes ago, SpartanVTX said:

Thanks for this! I’ll admit that I’m a total novice on these things (trying to learn as much as I can without causing myself more problems haha).  I understand the general concepts, but well aware of when I’m into an area I don’t understand yet! I wouldn’t even know where to begin to look if I screw up the gasket and need to replace it. 
 

I just ordered the cap and rotor to have on hand when I ultimately pull the plenum off to check things.
 

Incidentally, the flame arrestor looks to be kind of jammed in there as well, maybe it’s not actually the correct one? (Trying to figure out how to post a picture of that now…)

The K&N filter is a pretty tight fit where it sits.  Should be a cone shaped filter.  Just leave it on the throttle body.  There is no reason to remove anything but the 6 bolts and the wiring to the throttle body (and maybe one other sensor on the plenum)

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Normal for the K&N to barely fit on my direct drive Monsoon 340. It's slightly crushed by the engine box. Sounds like yours is the same, so don't worry about it. But feel the bottom of it for too much oily residue. If it's dirty and oily, then clean it. No need to replace it. K&N's are re-usable.

Don't strip the holes that hold the distributor cap on. It must happen a lot, because the distributor caps come with a set of screws with different threads, in case you do strip them (the thread holes in the distributor base are plastic).

I use a magnetic bit driver and a piece of tape to hold the screw to the bit, until I get the threads started. It's easy to lose a screw on mine because there's no way to place the screw in the hole.

 

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  • 2 weeks later...

Had started to take a look at all the different things mentioned hear when my neighbor mentioned that he had a strange problem with his boat involving the MAP sensor in his boat getting wet from condensation. Well, we removed the sensor and sure enough it was wet. After blowing it out with compressed air and making sure it was dry, we dropped it in the lake to see how things went. It had a rough start up, but then started running smoothly again. 
 

I then made sure to burn through all the gas that was in the tank before putting some new rec fuel in. So far, it has been running smoothly since we dried the sensor and got the potentially bad gas out of the system. Fingers crossed, that particular issue is behind me.

Thanks for all the assistance! I’m sure I’ll be back asking more newbie questions next year!

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Interesting.  I hope it is fixed.

Pressure sensors generally don't like compressed air because the diaphragm either stretches or punctures with too much pressure.  Sounds like it is still working, though.

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