Speed sensor problems

[Sturgeon Sticker]

I have a 1998 135 HP MERCURY OPTIMAX outboard and I keep having trouble with the speed sensors. I have had it worked on three different times and they can't seem to figure out what the problem is. It usually goes off when I am running around 4000 RPM for about 10-15 minutes and the buzzer goes off and immediately the motor RPM drops to about 900. I let up on the throttleand come to a stop and the buzzer quits and then I can take off again with no problem. Does anybody else have that similar problem with the same motor. Would appreciate any info.

Thanks

[Starfish]

Doesn't necessarily sound like a speed sensor to me... maybe oil pump or temperature sensor (perhaps actually overheating)? Is there a reason you think it's a speed sensor?

[luckyr]

I think starfish may be on to something. My brother in law had a simlar problem with his oil level sensor wire grounding out. The dealer had nipped off the sensor wire under the cowling and bypassed it from the tank to the in dash buzzer, the one under the cowling would bounce around and ground ever once in a while. His was a Yamaha though. Good luck

[Sturgeon Sticker]

the last time I had it in for adjustment and they had it hooked up to the computer it showed how many times the speed sensor had gone off. They called Mercury and they thought that it might be the idle linkage when you shift it in neutral. So they changed the linkage. It used to go off when I would start the motor but since they changed the linkage it doesn't do that anymore it just does it when you are under power after a few minites like I discussed the first time.
Thanks for the info: