Mercruiser 3.0LX Shift Interrupt Function

[CPro]

Hey guys,

Thanks for the advice posted to my thread from yesterday. The long and short of the symptoms I've been experiencing is that the boat won't rev over 2500 while in gear & under load. It backfires, sputters, and will stall if you catch it wrong. I've replaced all the fuel filters, rebuilt the carb, and replaced all the ignition components except for the pickup coil (which tested fine).

One thing I noticed - the shift mechanism does not seem to be fully releasing the shift interrupt switch. The switch has a lever arm with a roller (which rides in a V shaped arm) which looks like it is intended to momentarily depresses/releases a microswitch as you shift from F to N to R. My shift mechanism doesn't seem to be doing much...it nudges the interrupt switch almost imperceptibly..there is definitely not much action imparted to the switch. Should this switch be moving noticeably? Is it possible that the switch is stuck "half on"; i.e., not enough to completely kill the engine but enough to retard timing or spark?

My latest train of thought is that the shift cables are bad and have the shift interrupt switch locked into an "almost on" position..and that this is causing problems.

thanks again & in advance for any thoughts you may have on this! Fishing season is here and I've been busting butt for a week trying to get out there...

Best,
Trev

 

[tystick]

Re: Mercruiser 3.0LX Shift Interrupt Function

sure sounds like a fuel issue - hows the pick up in tank?

 

[Bondo]

Re: Mercruiser 3.0LX Shift Interrupt Function

The Boat Has to be IN the water for the Switch to Work,...... At All........

You Still have a Fuel Delivery Issue............

 

[Don S]

Re: Mercruiser 3.0LX Shift Interrupt Function

The shift interrupt switch is just that, a switch, it's either on or off, no partial on. If it's engaged, the engine will not run, cause the spark is stopped.
If you still think it might be the switch, disconnect it and go for a run (ON the water), but you will have to hook it back up to pull it out of gear, or shut the engine off.
Here is a thread that may help you locate your problem assuming your problem is actually a fuel related problem.

http://forums.iboats.com/showthread.php?t=167561

 

[linkhorn]

Re: Mercruiser 3.0LX Shift Interrupt Function

I just experienced the same problem. The problem was solved by removing the anti siphon device at the top of the fuel tank. It was partially clogged, allowing the boat to run well at 3000 rpm but lose power above that.

It can also cause the boat to stall when shifting into gear.

If you have a fuel filter, go ahead and remove the anti siphon and also remove the screen at the end of the gas pick up tube. The fuel filter will pick up any disbris. Change your fuel filter twice a year now.

If you still have shifting problems you can adjust the interrupt switch by disconnecting the cable at the switch and using 1/4 turns adjust the cable until you get the right fit.

Jim

Hey guys,

Thanks for the advice posted to my thread from yesterday. The long and short of the symptoms I've been experiencing is that the boat won't rev over 2500 while in gear & under load. It backfires, sputters, and will stall if you catch it wrong. I've replaced all the fuel filters, rebuilt the carb, and replaced all the ignition components except for the pickup coil (which tested fine).

One thing I noticed - the shift mechanism does not seem to be fully releasing the shift interrupt switch. The switch has a lever arm with a roller (which rides in a V shaped arm) which looks like it is intended to momentarily depresses/releases a microswitch as you shift from F to N to R. My shift mechanism doesn't seem to be doing much...it nudges the interrupt switch almost imperceptibly..there is definitely not much action imparted to the switch. Should this switch be moving noticeably? Is it possible that the switch is stuck "half on"; i.e., not enough to completely kill the engine but enough to retard timing or spark?

My latest train of thought is that the shift cables are bad and have the shift interrupt switch locked into an "almost on" position..and that this is causing problems.

thanks again & in advance for any thoughts you may have on this! Fishing season is here and I've been busting butt for a week trying to get out there...

Best,
Trev