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Mate
Posts: 0
Registered: ‎08-23-2018

175 etc 2010 Motor Changes RPM, Rough at 1500 RPM

Issue: Motor loses RPM without touching throttle then may or may not recover on its own  - Does not stall or throw codes but RPM varies even at idle. Always starts right up. Never overheated. When it runs good it is  flawless good gas consumption. Speed WOT 28 - 30 knts on 20 ft Sea Ox Walkaround. Prop 14 3/4 X 17 SS (5200 RPM) originally had 15x15 but cavitated 

 

Symptoms: Boat runs at 28kt @ 5200 RPM then randomly (instantly) loses 500 or more RPM and decreases speed. Difficult to accelerate between 1800 and 2500 RPM stutters and hesitates badly. Seems to be getting progressivley worse doing RPM drop at low speeds now.

 

Replaced the following with all new parts: Coils, TPS sensor, Fuel Pump, cleaned VST filter numerous times, new plugs (indexed) / wires, Exhaust relief valve, thermostats / housing, checked fly wheel (magnets intact – No rust) / 55-volt constant voltage output (computer confirmed), volt meter indicates 14.2 V output, checked and cleaned all wire grounds, replaced head gaskets, all new gas lines from tank to motor (E10 rating), 10 micron fuel / water separator (no water or sediment), new gas tank, checked vent line, water pump every 2 years.

 

Tech used computer to do EEM / Engine diagnostics on the water test. Turned off each cylinder one at time (500 RPM) difference. #4 cylinder only made 250 RPM difference. Naturally there were no codes. Engine hours  1400 -1500 most at idle or 4200 RPM

 

Model Number: E175DPXIIB

Serial Number: 05291875

Manufactured date: 07/2010

 

Sorry about earlier confusion

Any help is appreciated thank you

 

Blood N Guts

Captain
Posts: 61
Registered: ‎07-10-2017

Re: 175 etc 2010 Motor Changes RPM, Rough at 1500 RPM

First of all, awesome to see so many hours on your motor.  Obviously gets used!

 

You're RPMs seem to be too low at WOT.  Target RPMs should be at the top of the range with a light loadYou said the 15p prop cavitated, but that's generally a condition of height, not pitch. Not saying the prop is causing your variable rpms, but overtime it can put undue stress on the motor.  

 

Were all those parts replaced at the same time or over a period of time?

 

Good luck.

2017 Tidewater 1910 Baymax
Evinrude 150HO (M: E150HGXABH S/N: 05500627H MFDate: 6/17)
Admiral
Posts: 7,495
Registered: ‎07-14-2011

Re: 175 etc 2010 Motor Changes RPM, Rough at 1500 RPM

Is 5200 the highest rpm it will go at full throttle or was that just a speed and rpm statement?

 

 

 


"There is never just one thing wrong with a boat";
                    -- Travis McGee, main character in a book series by John D. McDonald 


 



***************

The factory recommends that a properly trained technician service your Johnson or Evinrude outboard motor. Should you elect to perform repairs yourself, use caution, common sense, and observe safety procedures in the vicinity of flammable liquids, around moving parts, near high-temperature components, and working with electrical or ignition systems.

The information offered here is only general in nature and should not be construed as complete factory approved procedures, techniques, or specifications. Always use the proper service manual for your motor, up-to-date service literature, the correct tools, and have an understanding of how to proceed with troubleshooting and repair methods. If you are unsure or uncomfortable with a procedure, a situation, or a technique, enlist the services of a factory trained technician.


Captain
Posts: 285
Registered: ‎08-20-2017

Re: 175 etc 2010 Motor Changes RPM, Rough at 1500 RPM

Speed WOT 28 - 30 knts on 20 ft Sea Ox Walkaround. Prop 14 3/4 X 17 SS (5200 RPM) originally had 15x15 but cavitated

This reads as though your not rpm is 5200 indicating that you are over propped thus causing higher loads on the engine. Also on most hulls 1800-2500 rpm is not on plane yet therefore plowing through the water causing a high load.
A possible cause of surging/rpm drop under high load conditions could be fuel starvation due to a fuel restriction or air in the fuel. A test with a vacuum gauge and clear tubing inserted into the fuel line at the engine connection should be performed. Another option is to try running on a 6 gallon portable tank with a 3/8" Barb connection (no quick connect on tank).

"15 pitch cavitated". Could be engine height or transducer too close to the engine. Also there can be great differences in the " bite" of various 15 pitch props. Sometimes deckboats are set up with pontoon style props which have big ears and very little cup to the blades to give good boat control and reverse thrust, where a v type planning hull would use a double or tripple cupped long narrow blade to give higher bite and speed.