96 spx 717 starts but dies after a few seconds. restarts but same happens

[bmongrain]

Couple of questions for the more experienced mechanics .
1- what are the signs of the mpem going bad?
2- sounds like a fuel issue to me , just had carbs rebuilt ....possible fuel lines? they are the old grey ones.
3- whats the symptoms of a kill switch malfunctioning? and is this circuit normally open or closed?
thanks guys
bill

 

[B_PWC]

Is the shutoff time very specific? Say every 15 seconds, exactly? That could be a sign of the MPEM.

Do you have an inline fuel filter? Any light green translucent goo in the filter or on the spark plugs? If the gas lines are original I would replace them regardless if they are causing the problem; because they will cause an issue eventually. Also check the fuel selector switch to make sure it is clear of goo.

I had the same issue with my 92 xp and the problem was the pickup lines inside the tank eroded and cracks in the line. So it only sucked air. It would run for about 3 seconds then die because of lack of fuel.

You can always test the kill switch with a multi-meter....

 

[bmongrain]

Thanks for your post today.
Engines starts and dies within 2 to 3 seconds . being a 96 spx 717 i thought it has just a start kill switch. But just for fun I tried the DESS self diagnostic test . Short beep long beep after five pushes on the start button. put the laynard back on and push start and get the code of two short beeps. code reads mpem cannot read digital code of lanyard or bad wiring in lanyard. this unit is sporting an old overton's lanyard generic multi fit (lots of caps and clips). so is it possible that it has dess and i didnt know or would i get the same codes for a bad regular kill switch.

 

[B_PWC]

I see you have another post regarding this issue.

For those that are following this thread or will read it in the future can you confirm it was the MPEM?

 

[Rotor13B]

Try cleaning the inside of the lanyard cap with an pencil eraser. the metal contacts can get dirty and not give a good connection.

 

[Bills86e]

1996 SPX has a DESS capeable mpem, but is non-dess stock. Someone would have had to change the saftey switch and have the mpem programmed to activate a DESS slot.

My guess is if you pull the return fuel line off the PTO carb, no gas will come out when you attempt starting. (fuel delivery problem).

 

[bmongrain]

thanks bill will check that tonight but dont think its the problem. i have disconnected the black with red stripe wire coming out of my mpem. restarted and it runs fine... like a top. so i replaced mpem and nothing changed. maybe a bad rectifier? it kills power to guage first then motor stalls . battery new connections tight