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High speed hesitation 1989 9.9 4 stroke

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  • High speed hesitation 1989 9.9 4 stroke

    at crusiung speed for years this motor would intermittently fall back to idle speed for a few seconds, then surge back up. Usually would start happening afer 5-10 mintues and then repeat at 5 minute intervals.No problems starting, idles fine. This year it got worse. I finally fixed it:
    First I noticed that the green oil pressure light was blinking off when this happened. The engine computer(CDI) on this motor forces it back to an idle if it thinks Oil pressure is low. So first I bypassed the oil pressure sensor by disconnecting the wire from it. No change! Then I disconnected the red/yellow wire going from the CDI processor unit pink pigtail wire to the oil sensor. No change. However, if I grounded the pink pig tail wire, exactly the same symtom occurred. So I concluded that the pink pigtail is frayed and grounding out somewhere. So, I dismounted the CDI from its bracket and inspected the wire bundle coming out of it by unwrapping the plastic wrap protecting it. Everything looked fine but there was some crud built up.. So I sprayed everything with electrial parts cleaner. then coated the pink pigtail wire with liquid electrical tape to clog any microscopic holes in the insulation. then rewrapped the bundle, but left the pink pigtail wire outside the bundle. Eureka! problem solved. And it runs better than it did 20 years ago when I bought it! There must have been a tiny crack in the pink pig tail insulation that was shorting to ground through some crud that was buidling up in the wiring bundle.

  • #2
    Revs limiter or low oil pressure

    That is one way to look at it. But based on the wiring diagram, the oil pressure sensor is the only input wired into pink. I ssume it also cuts back revs if it overheats, so there must be another input for the temp sensor.
    Older high tech engines have been messin with my head for years. After 10 years the sensors or sensor circuits get flakey and mess up the operation of an engine that is perfectly fine mechanically. Makes you wonder if all the electronic crap is worth it. If you are into physics, it is Heisenberg's uncertainty principal coming into play: "you cannot observe something without in some way changing it". The sensors are the observers.