Acceleration stumble when cold

[H2oskier13]

I have a 13 Reaponse TXI with the Monsoon 350 SS engine. When accelerating cold to pull a a skier up the engine rpm drops momentarily and then picks back up. This only ever happens when it’s cold on the first run of the day. It has never acted up any other time. With no skier and cold I can make it happen once on the first pull but cannot make it happen again even if I immediately stop and go again. 

Any ideas?

Edited May 5, 2018 by H2oskier13

[skurfer]

When is the last time you cleaned your flame arrestor and the flap underneath? Also, when is the last time you changed your fuel filter, cap/rotor/spark plugs?

[H2oskier13]

I’m not sure what you mean by flame arrestor, I have an air filter and it is clean. As for plugs, cap, rotor and fuel filter they are all original. If there was a problem with one of those items I would expect the stumble to happen more often than only when it is cold on its initial acceleration run. 

[Woodski]

@H2oskier13:  When the intake tract is cold, the fuel has trouble atomizing with the cold air so I would look towards the fuel system - a dirty injector would shoot a less atomized mixture compared to a clean one which would lead to a stumble condition.  You might want to have the injectors cleaned.  Do you warm up your engine before that first pull or start you ski run only after idling to the start point?  As your ignition parts age, it will take more voltage to create a good spark, so corrosion on the cap and worn plugs (increasing the gap) will contribute to cold operation issues.

[electricjohn]

Loose hose or vacuum leak on the intake system contribute to hesitation.

[JasonK]

Do a tune-up. It's due for one.

[lake4life]

@H2oskier13 I know this is an old thread but my 2013 Monsoon 350 SS is doing the exact same thing as you describe in your first post.  Where you able to resolve this?

[justgary]

2 hours ago, lake4life said:

@H2oskier13 I know this is an old thread but my 2013 Monsoon 350 SS is doing the exact same thing as you describe in your first post.  Where you able to resolve this?

So many things could cause this.  Have you done any of the maintenance that was suggested?  Tune-up is first, for sure.

I would:

• Do a complete tune-up including plug wires
• Clean the inside of the throttle body with carb spray, including the IAC port in the side wall
• Clean the spark arrestor with carb spray or soap and water (off the boat)
• Check the ECM engine temperature sender with an ohm meter to make sure it is working correctly

[lake4life]

3 hours ago, justgary said:

So many things could cause this.  Have you done any of the maintenance that was suggested?  Tune-up is first, for sure.

I would:

• Do a complete tune-up including plug wires
• Clean the inside of the throttle body with carb spray, including the IAC port in the side wall
• Clean the spark arrestor with carb spray or soap and water (off the boat)
• Check the ECM engine temperature sender with an ohm meter to make sure it is working correctly

Thanks for the suggestions.  So far I changed plugs, plug wires, cap, rotor, cleaned out the spark arrestor.

I'll check out the ECM engine temperature sender when I get a chance.

Other suspects already on my list are fuel filter and injector cleaning.

Only does it when it's cold for the first couple accelerations, then purrs for the rest of the day no matter how long it sits off.  Also, doesn't do it all the time when cold.  Seems to have to sit for a least a couple days.

Edited June 7, 2023 by lake4life

[justgary]

8 hours ago, lake4life said:

Thanks for the suggestions.  So far I changed plugs, plug wires, cap, rotor, cleaned out the spark arrestor.

I'll check out the ECM engine temperature sender when I get a chance.

Other suspects already on my list are fuel filter and injector cleaning.

Only does it when it's cold for the first couple accelerations, then purrs for the rest of the day no matter how long it sits off.  Also, doesn't do it all the time when cold.  Seems to have to sit for a least a couple days.

It is probably worth putting a fuel pressure gauge on it and watching it when it stumbles.  The pressure should be constant with key on, at idle, and at wide open throttle.  Maybe the pump is lazy for the first few minutes and not giving enough pressure, which would lean the mixture.  When the engine warms it will run closed loop and allow the integrators to enrich the mixture a bit.

My thought about the temperature sender is that the ECM really has to enrich the fuel mixture when it is cold to get enough fuel into the cylinders, as @Woodski mentioned.  If the ECM thinks the engine is even a few degrees warmer, it may lean the mixture too much.  Once the engine warms a bit it wouldn't really matter that much, and definitely not at all after the ECM switches to closed loop operation.