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So I need some help, actually the service technicians at Tommy’s and I both need help. I have a 2017 Axis A24 with the PCM 409 in it with 575 hours on it. Recently I have been having engine trouble as the motor has been running really rough at idle and in gar under power. It has been running below optimum performance and has a significant loss of power, wont even throttle over 4000RPM under heavy load. It has been throwing a MIL code with a service engine alert constantly and only way to clear the code is to reset the batteries only to have the code reappear. It is all under warranty, so I took it to Tommy’s for the service department to diagnose the service engine alert and they told me today that there is a cylinder misfire on cylinders 5 and 6 with the occasional 4. The misfire is constant but here is the problem, they cannot for the life of them identify what is causing it. They have ruled out everything with the ECM, fuel system and ignition system. They did tell me though that they have recently identified this EXACT situation with about 6 other PMC 409s regardless of year or hours on the other motors. They are so stumped about these boats that all have the same issues and same scenarios that they are calling in a PCM engineer to come and completely break down one of the engines to diagnose what is wrong mechanically. Tommy’s actually asked me if I could check the forums to see if anyone else has seen these issues. Any thoughts?

Edited by SJRwake
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I am sure they checked it, but I had a similar issue on my M5 @ 16 hours. Turned out it was the plug wires on #7 and #8. The dealer had to call Malibu to figure that one out.

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I am sure they have, but they need to reach out to PCM if they have no idea what’s causing the problem. I guarantee PCM will figure it out. 

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When there are constant misfire alarms it is common to perform a compression test to ensure all cylinders are capable of making similar power.  If the engine is mechanically sound and the compression is within specification, identifying other issues that can cause misfires can be initially identified with an injector kill test.  Repairs of any internal mechanical problems will likely be delt with at PCM.

An injector kill test using diacom can quickly identify cylinders that may not be making power.  It is normally done under load around 2000-3000 RPM.  Any cylinder that does not drop in RPM the same amount would be suspect.

Swapping components like spark plugs, ignition coils, or fuel injectors from a suspect cylinder to a good cylinder can help to find a faulty component.  If a previously good cylinder becomes suspect during the injector kill test after swapping a component, then the component that was moved to that cylinder is the likely cause.  If the original suspect cylinder does not perform better after swapping the components, then there is likely an issue with the wiring or connectors that go to the components on that cylinder.  Testing can be done to the circuits to find the problem.

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32 minutes ago, csleaver said:

When there are constant misfire alarms it is common to perform a compression test to ensure all cylinders are capable of making similar power.  If the engine is mechanically sound and the compression is within specification, identifying other issues that can cause misfires can be initially identified with an injector kill test.  Repairs of any internal mechanical problems will likely be delt with at PCM.

An injector kill test using diacom can quickly identify cylinders that may not be making power.  It is normally done under load around 2000-3000 RPM.  Any cylinder that does not drop in RPM the same amount would be suspect.

Swapping components like spark plugs, ignition coils, or fuel injectors from a suspect cylinder to a good cylinder can help to find a faulty component.  If a previously good cylinder becomes suspect during the injector kill test after swapping a component, then the component that was moved to that cylinder is the likely cause.  If the original suspect cylinder does not perform better after swapping the components, then there is likely an issue with the wiring or connectors that go to the components on that cylinder.  Testing can be done to the circuits to find the problem.

They did perform a compression test and all cylinders are holding optimally at about 185psi solid. I suspect it might be the distributor cap/rotor. I just changed all plugs about a month ago.

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31 minutes ago, SJRwake said:

I suspect it might be the distributor cap/rotor.

I surely hope that Tommy's isn't stumped by that....

32 minutes ago, SJRwake said:

I just changed all plugs about a month ago.

Did the problem start after you changed the plugs?

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4 hours ago, SJRwake said:

They did perform a compression test and all cylinders are holding optimally at about 185psi solid. I suspect it might be the distributor cap/rotor. I just changed all plugs about a month ago.

A pcm 409 has a distributor cap?

 

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Interesting, I have a PCM 409 in my 2019 23 LSV and had a misfire earlier this season.  I had about 120 hours on the boat at the time and they just completed a software update and a tune up.  The boat also ran really rough at low speeds and when ballasted, although I didn't notice any notable lack of power.  They brought the boat in, did some testing and determined it was running down one cylinder.  Took the boat out the next weekend and it was still throwing the same code and having the same problem.  They took it back and tested and tested, including  a compression test that showed up all good.  They tested it on water for several hours and it has been totally fine ever since.  I have probably 20-30 hours on it since.  But it almost sounds like a software issue or something...

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4 hours ago, justgary said:

I surely hope that Tommy's isn't stumped by that....

Did the problem start after you changed the plugs?

Yes but not immediately after I changed them, the dealership said that they changed the plugs again to be sure.

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1 minute ago, cmargosi said:

Interesting, I have a PCM 409 in my 2019 23 LSV and had a misfire earlier this season.  I had about 120 hours on the boat at the time and they just completed a software update and a tune up.  The boat also ran really rough at low speeds and when ballasted, although I didn't notice any notable lack of power.  They brought the boat in, did some testing and determined it was running down one cylinder.  Took the boat out the next weekend and it was still throwing the same code and having the same problem.  They took it back and tested and tested, including  a compression test that showed up all good.  They tested it on water for several hours and it has been totally fine ever since.  I have probably 20-30 hours on it since.  But it almost sounds like a software issue or something...

That sounds very similar to mine. It runs rough on idle and in gear but will run ok wide open on the throttle as long as the boat is not under heavy load with weight. If it is loaded then it will max out at 4000rpm and cant get on plain. Compression came back solid with all cylinders being at 185psi and holding. They said that they have only seen this problem on 409s and not the 450s which to mean sounds like a tuning issue since they are the exact same mechanically except for different tunes.

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Interesting that it happened to both your boat and mine right after a change of plugs, as well....

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I'm not sure what they did to mine, but my dealer / service center in Munson Marine in Volo, IL.  You might tell the guys at Tommy's to call Mary Jo, who runs the service department, maybe she can help out.

 

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I honestly don't know what plugs they put in the boat, I had the tune up done by the service center.  But it would seem logical that changing plugs is part of the tune up.

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