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1988 Evinrude 175hp power loss

Z

ztnark

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I have a 1988 Evinrude 175hp outboard on a 19' Starcraft Stinger Ski Boat. It has run flawlessly for me for years. However this summer it started acting up on me and has been very frustrating trying to diagnose the problem. It starts and idles roughly at first. Then after accelerating and getting up on plane, it will suddenly cut out and go to half power. The rpm's will drop to 3000 and it will barely move although the throttle is fully advanced. If I bring the throttle back to neutral and re-accelerate it, it will usually go to top speed again. Sometimes not. After this happens once or twice it may run the rest of the day without any problem. I changed the fuel filter and replaced the primer bulb which seemed to be cracked but it still persists. A friend of mine who is a boat mechanic looked at it and thinks its a faulty VRO pump. He said there is a low oil flow sensor on it that will shut the motor down to under 3000 rpms if the oil flow fails so the motor will not blow. He suggested I replace the VRO pump. I am not convinced this is the problem because I have been tending toward an ignition fault myself. Does anyone have any suggestion?
 
A low oil flow or no oil would not cause the engine to drop to 3000 rpm. It would however energize the warning horn system. Is your warning horn system functionable?

(Testing Warning Horn)
(J. Reeves)

On VRO equipped engines where the VRO automatic fuel/oil setup is still being used, make sure that all components are connected as required. This would include the VRO pump wiring harness itself, the oil tank wiring, the overheat sensor(s), and if so equipped.... the vacuum switch that is standard to many V6 & V8 engines.

If the VRO automatic setup has been eliminated and has been disconnected properly, and the fuel and oil is being premixed, make sure that the overheat sensors are still connected, and the vacuum switch if the engine is so equipped.

On engines prior to 1984 which have no VRO setup, ignore the instructions pertaining to the VRO components, etc above.

Turn the key to the ON position (Engine Not Running). Find the TAN wire at the cylinder head(s), then ground out the portion of that wire that is part of the engine wiring harness. If that Tan wire connector has the knife type connector where as it is exposed simply by sliding the rubber insulator back, it does not need to be disconnected.

Grounding that TAN wire should cause the horn to sound. If it does not, find out why as that's the only warning you'll receive should the engine overheat or have some portion of the VRO system fail, or have the engine encounter a fuel restriction if it is equipped with a vacuum switch.

(VRO Horn Warnings)
(J. Reeves)

NOTE: I retired around 1991/92. Possibly some of the later V4 engines and others may also incorporate a fuel vacuum switch that would enable a fuel restriction warning to sound as mentioned below, an unknown factor to myself.

1 - A steady constant beep = Overheating - The V/6 engines, possibly some others, have a fuel restriction warning which is also a steady constant beep.
2 - A beep every 20 or 40 seconds = oil level has dropped to 1/4 tank. (Late model engine = Every 40 seconds)
3 - A beep every other second = VRO failure, air leak in oil line, oil restriction, (anything that would result in a lack of oil being supplied to the engine).

NOTE - If the warning horn is the black plastic (overpriced) three wire type horn, the warning horn should beep once when the ignition key is turned to the ON position. If it does not, it is either faulty or someone has disconnected it (a stupid move!). At any rate, if it does not beep which indicates that the horn is non functional, find out why and do not run the engine until the problem is corrected.

If that engine incorporates what is called the S.L.O.W. feature, overheating would result in having one bank lose ignition, effectively dropping the rpms down to approximately 2500 rpms.

Trouble shoot....... Check compression, check igniton/spark which should jump a 7/16" gap with a strong blue lightning like flame, a real SNAP! The 7/16" gap is important.
 
Thank you Joe, I will check the warning horn connections because it does not seem to be working. It did early in the season but now that you mention it, I dont hear it when I turn the key to on as I used to
 
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