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Little mid season fuel system clean


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I had posted in another topic that I felt like my Monsoon was a little down on power this year. I already went through the ignition side of the house (which needed to be done badly) so I moved on to the fuel side today ( I ran it out of fuel a few weeks ago which didn't help). I replaced my IACV since I have been fighting this weird surging at idle in docking situations, in and out of gear / reverse etc... I replaced the fuel filter and blew out the intake screen on the fuel pump. I cleaned my throttle body as best as I could and then cleaned what I thought was going to be the MAF sensor. This is what I found when I pulled it out, is this a plenum pressure sensor or something? It doesn't look like a MAF to me? Anyway I cleaned it off with MAF sensor cleaner...

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All that gunk was pretty much covering the hole. Awesome. It runs WAY better now. I barley have to touch the throttle to get the thing on plane which was where I was noticing the most trouble. After seeing that junk come out of the intake plenum I am thinking that this fall I'll really tear it apart and clean everything. Send out my injectors etc...

For those of you who are wondering where the idle air control valve is its right on the side of the TB next to the TPS:

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Here it is removed:

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Also, if your looking to replace yours, the Borg Warner part # is 31023. I ended up getting a Standard which crossed to an AC147T. It was like $53 bucks from my local parts store.

Few questions going forward:

When I do my big service this fall will I need a gasket for the intake plenum? Can I remove the TB completely to really clean it good? Is there anything else I should do other than clean the TB, plenum and injectors? I thought about pulling that all apart today but not knowing if I needed a gasket I figured I'd wait.

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If your work already doesn't fix the issue you may want to disconnect the batteries completely so you reset the ECU. I thought I read somewhere when I was doing the work on mine that resetting the ECU after doing a TPS replacement was necessary so that it could re-learn.

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If your work already doesn't fix the issue you may want to disconnect the batteries completely so you reset the ECU. I thought I read somewhere when I was doing the work on mine that resetting the ECU after doing a TPS replacement was necessary so that it could re-learn.

I thought of that as well. I didn't replace the TPS (although the dude at the parts store told me I could just replace it without the whole re-learn thing). If I end up replacing it I'll have to do some more research

where was the clogged mystery sensor located?

Front of the plenum right behind the distributor cap.

Looks like MAP (Manifold Absolute Pressure) sensor. I dont think your boat has a MAF (Mass Air Flow) sensor.

After a little more googling I think you're right.

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If you pull the plenum and need a gasket, it is going to be a Malibu/Indmar part being that plenum was developed specifically for the Malibu Monsoon engine. Personally, I doubt pulling the plenum will do anything for you. If you want it cleaned, just run a can or two of Sea Foam in your gas. Making sure everything on the intake side of the engine is torqued to specs will also insure a smooth idle and out of the hole performance. The MAP sensor is perhaps the most critical component on the Monsoon engine.

Edit The 2003 Monsoon engine is known for its idle problems, called idle flair. Updating your ECM to the latest software version is supposed to fix that.

Smooth water man may know much more about that.

Edited by electricjohn
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