Need help with new-to-me Merc 115, died and won't start

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rpt50

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Very disappointing--I just bought a pristine 2016 Ranger aluminum CC with a 115 Mercury Pro XS 4 stroke. Ran fine on pre purchase test, and ran fine when I did a 20 min lake test after bringing home. Two days later, on our first "real" trip, it started sputtering about a half mile from the ramp, and then died and would not start.

Here's what I checked when I got home:
1. Tank is about 1/4 or a little more full (I had just put in 5 gallons of ethanol free with stabilizer).
2. spark plugs clean and dry
3. there is an in-line filter in the fuel line right after the fuel line enters the cowling, and it is bone dry.
4. I can hear a fuel pump running when I turn the key, but apparently the fuel pump(s) on this motor are housed inside the lower cowling. I don't want to remove that yet until I get more advice on how to proceed.

What do you think I should do next? It seems like it might be the lift (low pressure) pump, but are there other things I should check before taking the lower cowling off? Thanks!
 
? Huh
#3. no fuel entering the cowling ...fix that first.. the "LIFT PUMP" cannot suck from the tank without a prime.. that's what the bulb is for
? you don't mention any PRIMER BULB...
 
Sea Antsy said:
? Huh
#3. no fuel entering the cowling ...fix that first.. the "LIFT PUMP" cannot suck from the tank without a prime.. that's what the bulb is for
? you don't mention any PRIMER BULB...
Click to expand...
So tell me more! There is no primer bulb like all the outboards I have had before, but I have had stern drives and direct drives (ski boats) for the last 14 years. What do you think I have to do to prime the system when there is no bulb? I was thinking that there might be a pump in the tank (there are wires going to the tank) like in FI cars? Thanks!
 
disconnect the input to the filter just inside the cowling and BLOW hard... ? can you hear/feel yourself makin bubbles in the tank???
Is there a screen on the pickup tube.. .
 
Sea Antsy said:
be careful doin any dumb krap that I tell ya about..
Click to expand...
Don't worry, I'm in my 60s and still racing motorcycles. I know all about doing dumb stuff and surviving...

I'll look more closely at the tank tomorrow. I think I can get my compressor blow gun in there to take the place of my lungs. Thanks!
 
There is a low pressure lift pump and a high pressure pump inside the FSM (the little remote fuel tank under the cowling) on those, both electric. Pump failures are somewhat common. The whole assembly is about $900 from Merc, but you can buy aftermarket (or even the OEM Walbro pumps) and essentially rebuild it although the process is tedious.

There is nothing in the fuel tank but a pickup tube and a level sending unit. Also, they are not designed to have a primer, use of one can flood the system and cause fault codes.

If the pumps are running then that rules out anything electrical for the most part. Although the pumps are wired in parallel so one can fail and the other will still run.

You can stick a primer on the end of the fuel feed line to see if fuel can be drawn from the tank, and also to start a siphon. A siphon test will tell you if there are any air leaks in the line, ruling out that part of the system.

Priming the system is usually done by cycling the key a few times and allowing the pumps to run continuously for a short while, the fuel system on those must be purged of air as well for it to run, there is no return from the fuel rail.
 
Last edited:
MrGiggles said:
There is a low pressure lift pump and a high pressure pump inside the FSM (the little remote fuel tank under the cowling) on those, both electric. Pump failures are somewhat common. The whole assembly is about $900 from Merc, but you can buy aftermarket (or even the OEM Walbro pumps) and essentially rebuild it although the process is tedious.

There is nothing in the fuel tank but a pickup tube and a level sending unit. Also, they are not designed to have a primer, use of one can flood the system and cause fault codes.

If the pumps are running then that rules out anything electrical for the most part. Although the pumps are wired in parallel so one can fail and the other will still run.

You can stick a primer on the end of the fuel feed line to see if fuel can be drawn from the tank, and also to start a siphon. A siphon test will tell you if there are any air leaks in the line, ruling out that part of the system.

Priming the system is usually done by cycling the key a few times and allowing the pumps to run continuously for a short while, the fuel system on those must be purged of air as well for it to run, there is no return from the fuel rail.
Click to expand...
Thank you! Great information! It sounds like my course of action should be:
1. try to see if I can get a siphon going to test the lines to the tank, and if that checks out, then
2. pull the FSM and decide if I want to rebuild or just buy the whole thing
Please let me know if I'm misunderstanding something here. Again, thank you.
 
rpt50 said:
Thank you! Great information! It sounds like my course of action should be:
1. try to see if I can get a siphon going to test the lines to the tank, and if that checks out, then
2. pull the FSM and decide if I want to rebuild or just buy the whole thing
Please let me know if I'm misunderstanding something here. Again, thank you.
Click to expand...

Pretty much. If you are able to draw fuel from the tank and it siphons well, yet you still have no pressure at the fuel rail, you know that the problem lies in the FSM.

There should also be another filter under the cowl somewhere. Worth checking but not likely your issue.
 
MrGiggles said:
Pretty much. If you are able to draw fuel from the tank and it siphons well, yet you still have no pressure at the fuel rail, you know that the problem lies in the FSM.

There should also be another filter under the cowl somewhere. Worth checking but not likely your issue.
Click to expand...

Wow, this is working out very positively! I was unable to draw a siphon from the tank using various pumps and syringes I've got laying around from motorcycle work, so I took Sea Antsy's suggestion to blow into the tank and listen for bubbles. But even with my compressor blow gun and using my neighbor's stethoscope, we couldn't hear any bubbles. Then we realized that the air was blowing out from where the lines enter the cowling. Apparently there must be a coupler or something in there that has broken or come apart. It's going to be 98 today and the boat is nowhere near shade, but tonight or tomorrow I'll get back at it. But it's looking like a much less expensive fix now! Thanks for the help!
 
Sea Antsy said:
disconnect the input to the filter just inside the cowling and BLOW hard... ? can you hear/feel yourself makin bubbles in the tank???
Is there a screen on the pickup tube.. .
Click to expand...
This was a critical suggestion (see post 12 above). Thanks again!
 
Does it have an On-demand valve or is this pre-EPA venting requiremnet, Ie straight run to the tank?

If the former, they fail and prevent fuel flow. I believe you use a screwdriver to bypass them. It was new to me with our 2022 150 Merc.
 
I would install a fuel bulb. From what you have described, I suspect that you have a leak in the fuel line and the low pressure pump is pulling in air instead of fuel.
 
OP here. Turned out to be a connector that broke that (unfortunately) is made out to plastic and is kind of hidden in that protective hose that exits the cowling with all the control cables (see post 12). The part is integrated with the fuel line to the filter under the cowl, and was about $35. I'm going to keep an extra on hand as it seems like that part is really stressed every time you tilt up the motor, or open the cover in the rear of the boat. Apparently no bulb is needed on these newer motors. It just took a couple of key turns and I could see the filter filling up with fuel. It started on the next turn and took maybe 15 seconds to clear out and run smooth.
 

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