Engine issues. 1994 175 Merc XRI

8/4/15 @ 3:25 AM
ORIGINAL POST
Brody McWilliams
BMac_Fishing
USER since 5/7/15
Okay so I'm reaching out now. I'll explain what all has happened and how I'm speculating on what to do to see if anyone else has any different ideas. Okay so starting out this engine is used a lot I have used premium and normal gas. Always use Lucas oil ethanol treatment with a splash of quikleen every now and then. Engine probably gets at minimum 5 hours a week. So it starts: go to LaCrosse Wisconsin for college event. First day of practice about 10 hours on the water, quite a bit of idling too. Engine good. tournament day: put some gas from local gas station in boat, partner put a little bit too much ethanol treatment in it, didn't think much issue here... start day with a pretty short run, everything going good. About half way through day go for a bit longer run, run about 5 minutes then set down take off again and got to about 5000 ish rpms. (Granted boat normally ran at about 5200 with way prop and height is, needs fixed too, not the issue though) .. ¥once we got near 5k rpms it all of a sudden just lost rpms and speed to about 4k. Ran a bit more thinking it Wil kick back up it didn't. It bogged down a little bit more to around 3k rpms so I shut down and took off again, hole shot rpms stay right at 3.1k. Once on plane it once again got only to about 4k rpms. Long story short it is doing this still very erratically and random. At times it will get to full rpms, then all of a sudden it seems boggy again, not quite back down to 3k but 4kish, not as bad but still doing it, this was after putting 9 more gallons in to see if it was diluted. I plan on draining rest of gas tomorrow and putting full tank premium no ethanol in it with some seafoam tomorrow. Steps taken: checked primer bulb, pumped while running no help. Replaced all plugs and checked plug wires, all good there. replaced fuel filter, old fuel filter a tiny bit grimy and water sensor broke though. Pumped gas through into cup to see if water, no water at the time. Gas came through easily to so I don't suspect anything wrong with fuel lines. Have sense ran it and still kinda bogging down randomly, just not near as bad. I never had it drop off plane or shut down like most cases just not getting full rpms. Have also changed prop and hub to see if difference,no difference. Has not been overified revving. Just lost of top rpms at random. Anyone experience this or have any guesses? I'm also a broke college kid so can't be blowing money cleaning everything and tuning them by professionals. My thoughts of what it may be: Bad fuel, completely draining and putting in tomorrow to see if it solves it. Also will run seafoam with new gas to hopefully clean any junk that may have possibly built up. Next most likely things that I have read that sounds similar to my problem TPS loose or messed up, not effecting my idling though... maybe some minor short only getting triggered randomly? Stator.... unlikely since I am able to get full rpms every now and then. It just seems way more random than most the common problems so I'm hoping it is just fuel. Thanks for any help in advance! PS: checked compression on all cylinders, all at about 115 psi so good there too.
Edited on 8/4/15 3:27 AM
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Displaying 1 to 8 of 8 Posts
9/8/15 @ 6:31 AM
reeldrag83
reeldrag83
USER since 12/20/12
Agree spark issue.

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9/7/15 @ 8:42 PM
Trailblazer13
Trailblazer13
USER since 3/3/13
Hey my boat did this to me tonight on the water...just cruising along then bam drops 400rpms.....sat for a while fishing then back cruising I went then bam lose 400rpms....I'm trying to get a hold of a mobile mechanic to fix. I'll keep my eye on this to see what you find out....sounds like a pricy fix can't wait to sleep on the couch lol

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8/5/15 @ 5:43 PM
Plmlk
Plmlk
MEMBER since 12/18/07
Switchbox = Power pack / Tomato = Tomahto

Same deal, Rifleman and myself are on the same page - sounds like a spark issue!

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8/4/15 @ 6:46 PM
Rifleman1962
Rifleman1962
USER since 4/16/11
Plmlk.Is right that this is not fuel related and more spark related .I owned this motor and work on them. If you have Good Compression and without testing with a D.V.A meter. Sounds like your Switch Boxes are going out. You will have to replace them in a pair. Mercury or any Marina will tell you that or Me. If not replaced with 2 new Switch boxes. The old one will take out the one new Switch box, that you just replaced. You can get them after market. Pm me if any other ??????.

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8/4/15 @ 6:31 PM
Plmlk
Plmlk
MEMBER since 12/18/07
Also, I forgot to mention, I don't suspect bad fuel. As if you had bad fuel, your engine would run poorly all the time, not intermittently and random like you described.

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8/4/15 @ 6:29 PM
Plmlk
Plmlk
MEMBER since 12/18/07
How did the spark plugs look? You ruled out some of the basic fuel delivery problems that I would have suspected. It almost sounds like your power pack is intermittently failing, and dropping out one or two of your cylinders. That happened with my 150 horse power Evinrude intruder about 10 years ago. Long story short it was the voltage regulator that caused a power pack to go bad. I ended up replacing the power pack and the voltage regulator, and then the engine ran fine. The next time it does this for any length of time, pull out your plugs and look at them closely. If one of the cylinders is being dragged along for the ride, you should be able to see that in your spark plug. It is tough to diagnose without being there, but from your description, the power pack is at the top of my suspect list... Best wishes

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8/4/15 @ 5:30 AM
SnakeSter
SnakeSter
MEMBER since 7/9/12
Is the engine always at operating temp when it happens?

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