Response LXI with Monsoon 335 Runs rough won’t go over 20 mph. Weak power.

[Jedskier]

Hello,

I hope someone can help troubleshoot before the summer is over, our summers are short here in Massachusetts.

I have a 2003 response lxi with a monsoon 335. 

Engine starts up ok. Idle is decent sounding. Moving forward, there is loss of power. Opening up throttle will only get up to about 2,000 rpms and 20 mph maximum. And it is slow getting there. When I rev it in neutral. It will go to high rpms, but when I pull back the throttle to neutral it sometimes stalls. The air intake gives a hissing sound more than normal when changing to forward, or throttle coming back down to neutral.

here is what I’ve checked so far: fuel pressure is 40 at neutral and 48 when trying to move forward. Changed fuel filter. Put additives in fuel, star tron, stab il, sea foam. Changed MAP sensor, ITC sensor, water temp sensor. Unplugged oil pressure sensor (forward going to gauge) and pointing port side. Runs same with either disconnected. 

Oil pressure reads 20 when idle, goes to 40 when underway. Temperature gauge reads 160. 

Checked timing, it’s 20. Changed spark plugs, cap and rotor. 

A few years ago the alarm started sounding under the dash. Sounding all the time. The engine was running perfect and gauges were reading normal. So I disconnected the alarm. It ran for a few years after that running perfect. Until now.

 

 

[justgary]

The description sounds like it is starving for fuel.  Could be clogged injectors.  Could be an intake leak.  Does the 2003 have the big intake plenum and the throttle body over in the corner, or a regular looking intake manifold with the throttle body in the center?

It might be worth the effort to get a can of ether and spray it around the base of the throttle body and edges of the manifold/plenum while you are trying to accelerate the boat.  If the power suddenly jumps, you probably have a leak near where you were spraying.  Be careful so you don't get thrown out of the boat or into a pulley....

 

[tvano]

the ecm will limit rpm to somewhere near 3k if it thinks it should be in limp home mode.

iirc, temperature is one input that can cause limited rpm.  have you checked temperature sending unit(s)?

hoping the crew will chime in and list other stuff n things that will cause ecm to limit rpm.

note that the engine should run smoothly but limit rpm in limp home mode.

[Eagleboy99]

3k would be about 20 mph.

[justgary]

More like 30 in a Response. 

[rbert]

I had the same problem exactly, after over thinking the problem I went back to basics.  changed distributor cap and rotor,( they showed corosion), spark plugs (all fouled), ignition module and knock sensor and connector(connector had rusted off) and it runs like a top.  I suspect the ignition module was the main culprit but cant be sure.  

A tune up basically.   

[electricjohn]

I agree with ign module.

[Jedskier]

Update—- I sent the ecm to OBD Diagnostics in California, they found that the ecm is no good. It also showed a high current in the fuel injection code. They think I should be able to plug in the new computer and ready to go, but suggested before I do that, to test the ohms coming from the fuel injection bank. Incase it’s too high and could blow the new computer. Should be between 12 and 14 ohms. Any pointers on how to test this?

 

[Jedskier]

Boat all set! I tested the resistance in the fuel injectors, measures 12.5 ohms. Which is within range of 12-14, So put new computer in and started up and runs perfect. Thank you to those who replied with suggestions! 

 

 Update—- I sent the ecm to OBD Diagnostics in California, they found that the ecm is no good. It also showed a high current in the fuel injection code. They think I should be able to plug in the new computer and ready to go, but suggested before I do that, to test the ohms coming from the fuel injection bank. Incase it’s too high and could blow the new computer. Should be between 12 and 14 ohms. Any pointers on how to test this?