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03 Monsoon 335 Stalls Under Surging Idle


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Hello All,

 

Let me start with saying I have read at least 10 different threads on here for similar issues as mine but it seemed like none matched up perfectly so here I am. I also just bought my boat up today and wanted some insight before troubleshooting and/or taking to my mechanic. 
 

My issue: I start the boat, after about 10 seconds my idle will go from ~800 up to 1500. Now there are two scenarios: 1) if I engage throttle when still in the 800 rpm idle, I have no stalling issues but I can’t get above 4,000 rpm. I also think there is a lot of vibration / excess motor noise (it doesn’t sound like a smooth RPM band if that makes sense). The exhaust also smells very rich. 
 

2) if I engage throttle at the high idle (1500 RPM) the engine begins to stall immediately and even if I back off the engine rpm dives and eventually stalls. Once it stalls, I can restart the engine and the low->high idle process begins every time. 
 

The seller’s local marina checked codes and got both side A and B injectors. Now I’m not familiar with codes on this engine so if that sounds askew, bare with me for the time being. He also ordered injectors and reimbursed for 3 hours labor which his shop said was the rate for injectors - does 3 hours sound right? It surprised me that it was that low. 
 

From reading other threads, here’s what I’ve gathered to check:

IAC

TPI

Throttle body/plate for gumming, etc

Plugs for a rich / problematic cylinder

Fuel filter (and lines)

Water temp sensor that the ECM uses

Ignition Control Module

03 ECM Reflash

 

Based on my surging idle AND my unable to get past 4,000 RPM, any insight on how to prioritize that list and anything I’m missing? 
 

Only 270 hours on the boat/engine so it has sat a fair amount of its life but I’m told the issue started two weeks ago. 
 

Thanks in advance all, very excited to join the Malibu family. 

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The other thing I would add/correct is in the high idle state I can engage throttle enough to move forward (at a very high idle which makes a no wake speed nonexistent) but anything beyond that stalls the engine. 

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Uggghhhhh.  Did you at least test the compression before you bought it?

It could be injectors, but it could also be a long list of other issues.

The low hanging fruit is a complete tune up first (including wires), plus the throttle body clean up.

Your best bet would be on building a MEFI cable and reading engine data yourself.  That way you don't just throw a bucket of parts at it.

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22 minutes ago, justgary said:

Uggghhhhh.  Did you at least test the compression before you bought it?

It could be injectors, but it could also be a long list of other issues.

The low hanging fruit is a complete tune up first (including wires), plus the throttle body clean up.

Your best bet would be on building a MEFI cable and reading engine data yourself.  That way you don't just throw a bucket of parts at it.

The pick up on this engine makes me thing compression isn’t a factor. Also I’ll add the ignition wires look good if not recently new. I’ll be spending tomorrow checking through my list of potential root causes just wanted to seek additional advice here first 

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There are no codes for fuel injectors on an 04 Monsoon engine. Check your fuel pressure. My plug wires are still original and trouble free, As are my injectors. One of the most looked at sensors by the ECM is the MAP sensor. The other, RPM's through distributor reference.

Edited by electricjohn
changed 03 to 04.
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9 minutes ago, electricjohn said:

My plug wires are still original and trouble free, As are my injectors.

That doesn't mean that @RBBecker's are good.  Primary wires degrade over time and shouldn't be ruled out as a trouble source.  Injectors are also subject to clogging/hanging open issues.  If I bought a boat with a malfunctioning motor, I would not hesitate to change the plug wires in addition to the other tune up items.

It isn't clear why the shop didn't just diagnose the issue and fix it, but that ship has sailed.  Reading data with a MEFI cable will tell him which sensors work and which ones don't.  Actually, all of the sensors can be verified with a volt meter, but reading the values from the ECM tells you that it knows the correct values *and* that the sensors work.  Changing sensors that work is a waste of time and money.

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1 hour ago, dtm8119 said:

That's a good point.  I guess I was assuming that the shop already did that, but I don't see any reason to trust anything they did or say since they didn't just fix the problem.

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On 9/19/2021 at 7:04 AM, electricjohn said:

There are no codes for fuel injectors on an 04 Monsoon engine. Check your fuel pressure. My plug wires are still original and trouble free, As are my injectors. One of the most looked at sensors by the ECM is the MAP sensor. The other RPM's through distributor reference.

I change my rotor, cap, wires and plugs every 5 years, impeller, fuel filter, every 2 years and all oils every year. 

Have you put a multi meter on your wires to check for resistance, do you change your rotor or cap once in awhile?

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7 hours ago, malibu2004 said:

I change my rotor, cap, wires and plugs every 5 years, impeller, fuel filter, every 2 years and all oils every year. 

Have you put a multi meter on your wires to check for resistance, do you change your rotor or cap once in awhile?

Rotor and cap are changed by visual inspection. Never metered the wires. If engine stops running perfectly, I'll change wires, perhaps.

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