Failing throttle guardian

[Tim75]

Hello all.
Mercury 240 EFI. Challenger 2000.

Out today, engine stalled 3 times today, restarted easily.
Checked for water in fuel filters, vapor separator. Spark plugs oily, (too many no wake zones), compression 145-150 on all six. Checked TPS--OK.
Does anyone know the symptoms of a failing throttle guardian? Do they fail under heat, intermittent, or just dead? What happens to the engine when it does fail? I know these are commonly disconnected, but my wires are all crimped. I hesitate to cut wires not sure which to cut. Anything to disconnect at the engine?

Do either of the 2 electronic boxes on the top of the engine block ever fail?

Thanks.

 

[Dr Honda]

When the guardian starts to fail... it's intermittent... and does strange things. I disconnected mine before I even had the engine back in my boat. (I bought it with a bad engine)

The fast, easy thing to do, is to just disconnect it, and see how it goes.

I'm sure the boxes on the engine can fail... although, I haven't heard of anyone talking about them.

When you have an issue like this... where it dies, but restarts... I would be looking for a fray, or lose wire. Also... make sure the lanyard is still OK. If the rubber boot is getting lose... then that could cause a quick kill.

 

[Tim75]

Merc 240 EFI engine-
OK-- after testing the throttle guardian by revving to 3000and getting the TG to egage, reducing rpm, I found the dark DARK blue w/ yellow trace wire on top of starboard cyl. head. Shock hazard! Pulled apart the bullet connector and engine smoothed out perfectly. BUT the kill switch no longer worked. (The seadoo kill switch was replaced with a Merc unit $22 when I found the dealers charge $28 for that rubber cap and string.)

At the helm, next to the fuse block is the 2" x 4" guardian. As Doc H. has said, one snip and it is disconnected. At the local drive-in test stand on the trailer (aka tiny boat ramp on a canal), engine started quicker and ran smoother. However, on a test run, the engine still surges a lot and stalled once.

Is there anything else to disconnect on the TG?

 

[Dr Honda]

The TG wouldn't cause surging. it would feel like the key was turning on and off.

If you have a surge... you may want to check for a restriction in the fuel system, and the pressure at the regulator. As I recall... it should be around 36 psi.

 

[Dr Honda]

I was reading over the manual... and a surge at 4000 RPM can also be caused by a switch box going bad. But... I'm thinking your's is fuel.

 

[Tim75]

Trust the Doctor.
Checked lift pump & spin-on filters. Both OK. I started checking wires for breaks/corrosion. One wire on the vapor sep. pump was being held only by the rubber boot. It would run OK on the trailer, but bouncing in the water gave an intermittent connection. No pump=no go. Replaced both wire connectors (crimped & soldered), tested in the water and ran perfectly. I love repairs that only cost 20 cents. 5800 RPM, 48 MPH.