# 4 Stroke Merc still won't run !!!



## SSST (Jun 9, 2011)

Ok, I've had this boat in 2 Mercury dealers and 3 months later I'm in the exact place where I started, minus $1200. This is a 2004 Merc 115 4stroke and the problem is it bogs at 2k rpms and will not run any higher. Both shops said they ran it in the tank before giving it the ok, but when I put it in the water and hammer it, same ole ****. It's basically starving for fuel, I really think the problem is gonna end up being something so simple, but yet I don't have a clue what it could be. The injectors are fine, the hoses are all new, the water/fuel separator is new, all new plugs, and probably some things I'm forgetting. The gas tank was cleaned out also. This motor has very low hrs, it basically sat for the last 2 yrs, I bought it for a bargain or so I thought. Looking for any suggestions I can try before dragging it back to the shop again.


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## TrueblueTexican (Aug 29, 2005)

*Get the mechanic*

To take a ride with you -- still sounds like a fuel problem - likely still junk in the system -- that Merc is a Suzuki in disguise - I would suspect the high pressure pump is your culprit - there are TWO pumps on that motor - a mechanical boost pump that runs off the cam shaft and the high pressure pump located under the intake manifold.

I bought the same motor which sat with frickin ethanol in the system, when the water separated out and got to the high pressure pump, it grew algae in the system and had to get a NEW high pressure pump - after that ran like a top --


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## SSST (Jun 9, 2011)

Supposedly that pump is fine, but who knows.


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## LEDERMARINE (Apr 27, 2012)

Did either shop read it with diag software? If so I would check fuel pressure with gauge under load, either on a dyno or on the water.


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## Silver60 (May 12, 2010)

I would check the filter in the injector pump and have the injectors removed and professionally cleaned. Sounds like a ethanol issue


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## SSST (Jun 9, 2011)

Injectors were cleaned twice. Everybody is leaning toward the high pressure pump, makes me wonder if it was ever checked the right way. I don't think either shop hooked it up to a computer, I think they both thought they had the problem figured out. How much does a high pressure pump cost and can a guy with a little mechanical sense install one? If it's not too much, i'll just buy one and give it a try.


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## TrueblueTexican (Aug 29, 2005)

*Its labor intensive*



SSST said:


> Injectors were cleaned twice. Everybody is leaning toward the high pressure pump, makes me wonder if it was ever checked the right way. I don't think either shop hooked it up to a computer, I think they both thought they had the problem figured out. How much does a high pressure pump cost and can a guy with a little mechanical sense install one? If it's not too much, i'll just buy one and give it a try.


The pump isn't too bad , but you have to pull the intake manifold to get to it- take it out -

I'd bet 100 bucks a new one will solve the issues - to get my system cleaned, cleaned injectors, replace manifold gasket, new pump + labor was a 900 dollar bill --

It all started due to a 30 gallon tank half full and then the idiot dealer I bought it from not draining the tank in storage, THEN attempting to start a motor on 2 YEAR OLD FUEL --

First sniff off the tank and the high pressure pump was toast - the fuel had turned mostly to acid from sitting -


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## Silver60 (May 12, 2010)

I had a 115 Yamaha did the same thing there was a small screen inside the VST pump where the pump sucked the fuel ,it was slightly filled with gunk from the ethanol BS would idle fine and run up to about 1800 rpms then just fall on its face and back fire and try to Die


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## SSST (Jun 9, 2011)

This one idles great, runs about 2200 great, never misses a beat at 7.4 mph, lol. You hammer it and just bogs, come up with the throttle and it levels off and purrs fine. To me it's just getting so much fuel and past a certain point it just starves.


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## Silver60 (May 12, 2010)

What year model is it?


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## TrueblueTexican (Aug 29, 2005)

*Find a new shop*

That also services Suzuki and likely they will get you running - from your description its the High Pressure pump --


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## Silver60 (May 12, 2010)

http://www.boats.net/parts/search/Merc2/Mercury/115%20EFI%20%284-STROKE%29/0T801000%20THRU%201B226999/Fuel%20Injection%20Pump/parts.html[/IMG]
Part 14 is the filter In your VST might be the same pump that's on a yamaha since your power head is a yamaha


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## SSST (Jun 9, 2011)

Silver60 said:


> What year model is it?


2004, the guy I bought it from said it was made by Yamaha, I kinda just thought whatever, but apparently he knew what he was talking about.


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## Smackdaddy53 (Nov 4, 2011)

Have you made sure the fuel line is not getting pinched or kinked somewhere? My buddies Yamaha 70 4 stroke was starving for fuel only when turning and took to to the dealer several times and he finally traced it back himself. He found the fuel hose getting restricted because there was not enough slack between the motor and deck fitting and the hose finally got weak enough to make the motor sputter. It could be a similar issue.


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## Silver60 (May 12, 2010)

I don t know if it would help you it may not be the same fuel set up but here is a video on you tube but you can clearly see how the filter can cause problems watching the video
Watch "Yamaha F115 FS VST Filter Change Out" on YouTube
Yamaha F115 FS VST Filter Change Out: [MEDIA=youtube]gY2RFaahio4[[/MEDIA]


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## JED (Nov 14, 2004)

Take it to Mac at Chris's Marine. He will set you straight.


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## SeaY'all (Jul 14, 2011)

just out of curiosity, isnt there a vent on the fuel tank assembly? If it is only happening when you "hammer down" maybe the fuel restriction is at the assembly. Im not a mechanic but, I have heard of this problem before.


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## GulfCoast1102 (Dec 30, 2013)

If neither mechanic shop was willing to put the boat in the water NOT A TANK, and run it under load, you need to find a better mechanic!

Motors will NEVER run the same on a water hose with muffs, or run in a tank, as they will while pushing the boat across the water.

It sounds like some other folks have some experience with issues similar to yours, so hopefully you can figure the issue out yourself. I can't help you on your motor. All the motors i've ever owned have been old, clunky, 2-strokers with carbs. However, some things don't change. 

Just bugs me to hear of a mechanic who won't bother to properly put the motor under load and test it.


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## SSST (Jun 9, 2011)

SeaY'all said:


> just out of curiosity, isnt there a vent on the fuel tank assembly? If it is only happening when you "hammer down" maybe the fuel restriction is at the assembly. Im not a mechanic but, I have heard of this problem before.


One of the first things i did was bypass everything going to the motor, i just went straight from a 6 gallon tank, so i'm pretty sure the problem is somewhere between where the fuel line connects to the injectors, seems like it wouldn't be this hard to diagnose.


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## SSST (Jun 9, 2011)

GulfCoast1102 said:


> If neither mechanic shop was willing to put the boat in the water NOT A TANK, and run it under load, you need to find a better mechanic!
> 
> Motors will NEVER run the same on a water hose with muffs, or run in a tank, as they will while pushing the boat across the water.
> 
> ...


I'd take an old beat up 2 stroker right now, first 4 stroke i ever owned, and it won't be for long if i can just make it run, lol. Both dealers insisted running it in the tank was a sufficient test. May take it back to the last dealer, at least he's willing to work with me, first dealer was like tough luck!


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## GulfCoast1102 (Dec 30, 2013)

SSST said:


> I'd take an old beat up 2 stroker right now, first 4 stroke i ever owned, and it won't be for long if i can just make it run, lol. Both dealers insisted running it in the tank was a sufficient test. May take it back to the last dealer, at least he's willing to work with me, first dealer was like tough luck!


That statement is DEAD WRONG, and it is a sign of a mechanic who isn't interested in doing what it takes to diagnose the problem.

Further, were the mechanics (either of them) able to see the motor behaving as you have stated? If not, it lends further credence to my statement that a tank test isn't sufficient.

The motor simply will not load up and run the same when it isn't pushing the boat.

It makes about as much sense as starting your truck up in the driveway, leaving it in park, and insisting that the transmission doesn't have any problems. There is no way of knowing (short of obvious, major failure) whether you have a problem or not.

Load test, load test, load test!


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## mattfox (Jun 6, 2014)

This may be a dumb question, but its not way over propped is it?

Did it used to run fine?


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## SSST (Jun 9, 2011)

No, it ran fine.


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## Ramujet (May 10, 2006)

exact same issue with Yamaha 4 stroke 115, was the inlet screen on the intake of the high pressure fuel pump


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## LEDERMARINE (Apr 27, 2012)

X2 on load test. Try to use a shop with a dyno. We have one here in Freeport.


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## TrueblueTexican (Aug 29, 2005)

*Merc/Yamaha/Suzuki*

Just to be clear, pre Verado - Merc's 90-HP and 115-HP four-stroke engines were designed and manufactured by Yamaha. Mercury bought the power heads from Yamaha as an assembled part, and bolted it onto their midsection and gear case. These engines were not in the co-development and co-manufacturing agreement.

The block casting is sent to Japan , boring is done in a Suzuki heavy industries plant, the internals supplied by Mercury, assembly in Japan and block mated to Merc LU's - now that they are building Verados (parts sent to China for assembly and shipped back) they have ceased partnership with Yamaha.

Your 2004 engine is a mutt - head is a Yamaha, LU is Mercury, but basic design and fuel system in very similar to Suzuki --

Ain't globalism fun !!!!

You are a "victim" of CARB requirements, the Federal Government E gas, and globalism - as have many of us who were formerly black on back die hards have become -

Ethanol fuels have become a shops best friend - you would think most of them could diagnose Fuel Injection ethanol related problems by now --


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## EvansMarine (Jun 7, 2010)

It's a simple test to run fuel pressures under a load , also I have seen your issue over and over, many shops try and reuse the intake manifold gasket, will not work! Also dumb butts will mess with security torquex screws on butterfly's and get the intake vacuum out of sync. Yes YDS software should be hooked up regardless but these motors are several manufactures put together. Your motor actually uses yamaha YDS software to run diagnostics . But knowing the motors and lessons learned, if you have 34-38psi not dropping steady, then more than likely fuel pump or VST filter, if it's up and down, your not keeping up with load supply demand and you need to look for low pressure pump issue, fuel lines and or clamp leaks' venting of tank' fuel anti syphon valve, primer bulb and so forth ! You need to find a shop that knows your motor and get references of customers they have performed fuel related repairs on and call them.

Good luck


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## SSST (Jun 9, 2011)

Hmm, if this motor usesYamaha software then maybe Kresta's will actually take it in. I called them and they said no Mercs, but maybe this is worth a call. I trust those guys, they have never let me down. If not, looks like i'll be dragging it to one of you guys near Houston. I think it's over my capabilities. Thanks for all the responses.


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## BullyARed (Jun 19, 2010)

GulfCoast1102 said:


> If neither mechanic shop was willing to put the boat in the water NOT A TANK, and run it under load, you need to find a better mechanic!
> 
> Motors will NEVER run the same on a water hose with muffs, or run in a tank, as they will while pushing the boat across the water.
> 
> ...


I had a 85HP Suzuki 2-stroke and it had a similar problem. It idled great and couldn't make it over 2500RPM on the lake. I took it to the dealer and picked it up a week later. They said they cleaned the carbs, gave it a tune up, ran a tank test, and it worked fine. That's would be $300 sir! Took the boat home and the same sh!t wasn't fixed. Did some research and replaced the thermal sensor. The boat ran perfect!


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## EvansMarine (Jun 7, 2010)

First check fuel pressure on the fuel rail. You can buy a fuel injection drew on gauge at auto parts, back boat down on the ramp , put in gear, and see if gauge stay steady, and upwards 34psi. If that all good I would expect air leak on intake manifold, or someone messed with the butterfly sync. The only way to tell that is with a quad vacuum gauge kit like from k&l tool. If fuel pressures drop and raise back and forth it's fuel supply issues from tank to low pressure pump.


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## SSST (Jun 9, 2011)

EvansMarine said:


> First check fuel pressure on the fuel rail. You can buy a fuel injection drew on gauge at auto parts, back boat down on the ramp , put in gear, and see if gauge stay steady, and upwards 34psi. If that all good I would expect air leak on intake manifold, or someone messed with the butterfly sync. The only way to tell that is with a quad vacuum gauge kit like from k&l tool. If fuel pressures drop and raise back and forth it's fuel supply issues from tank to low pressure pump.


Better yet, where is Evan's Maine located?


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## EvansMarine (Jun 7, 2010)

We are in bacliff, tx about 2 miles south of Kemah. We have a 6week back log right now. But if we can't fix it, you don't pay. If we fix and you have problems with what we repaired in 3 months we warranty. We give 3 month standard warranty on all our labor, and manufacture warranty on all parts if purchased from us.


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## Ramujet (May 10, 2006)

yes , remove the high pressure fuel pump, clean the inlet screen on the bottom ( inside the bowl), reinstall it, and go. It will be that simple...


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## SSST (Jun 9, 2011)

Turned out to be the throttle position sensor, mechanic said he just kinda got lucky, computer showed it working, but he put a different one on it and that was the problem. He was glad to see me drag it off.


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## chumy (Jul 13, 2012)

SSST said:


> Turned out to be the throttle position sensor, mechanic said he just kinda got lucky, computer showed it working, but he put a different one on it and that was the problem. He was glad to see me drag it off.


Them dang TPS sensors, tap them with a hammer and sometimes they start working again. A vibrating outboard is a harsh enviroment for a potentiometer.
Automobiles are no different
Glad you fixed it.


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## SSST (Jun 9, 2011)

Lots of headaches for a $100 part, been in shops since May.


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## EvansMarine (Jun 7, 2010)

SSST said:


> Lots of headaches for a $100 part, been in shops since May.


Glad you got it fixed!


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## SSST (Jun 9, 2011)

EvansMarine said:


> Glad you got it fixed!


Thanks, i ran it hard yesterday, it'll turn 6k rpms and runs upper 40's, kinda surprised me. Turns out, this 2004 motor had 29 hrs on it, less than 3 hrs a year!


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## cva34 (Dec 22, 2008)

them kind make for sleepless nites for you and mechanic...GLAD Ya Got it!!!


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## Dnlstvns (Jul 1, 2013)

Tps sensor had me going nuts like u were on a yamaha 2 stroke. 3 mechanics couldn't fix it. Got a manual and it took me about hour to figure it out. You would think a descent mechanic would catch that but oh we'll. cost me 500$ for fuel pump and 500$ for carb cleaning. 


Sent from my iPhone using Tapatalk


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## SSST (Jun 9, 2011)

He said it never showed up on the diagnostics while running it on the computer, he thought it had to be trash in the system somewhere. I used to be a car mechanic, i understand the frustration on this type of deal.


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