Mercury 115 FOURSTROKE Won't Start

Repair or modification of Boston Whaler boats, their engines, trailers, and gear
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Joined: Fri Apr 13, 2018 1:25 pm

Mercury 115 FOURSTROKE Won't Start

Postby BWbert » Fri Apr 13, 2018 1:28 pm

Goodday all--I'm Bert and I'm a big fan of Whalers. I am currently working on a Mercury 115 FOURSTROKE that won't start. Where I can post about the topic?
[BERT--I moved your post to the REPAIRS and MODIFICATION FORUM--jimh]

Thank you

Posts: 27
Joined: Fri Apr 13, 2018 1:25 pm

2008 Mercury 115 FOURSTROKE Cold Starting

Postby BWbert » Fri Apr 13, 2018 2:02 pm

I am currently working on a 2008 Mercury 115 FOURSTROKE engine, and we are having some big problems starting this engine. A scan of the engine told us that we needed to change the fuel pump. So we did. No luck. After a bit of time, we bypassed the safety lanyard switch, and we then noticed that coils and spark plugs were working just fine. We tested the fuel injectors, but they worked too.

We finally sprayed some starting fluid inside the air intake--it has no sponge around filter--and the engine fired right up.

What we noticed then was that the engine will start when warm but will not start when it is cold, even if you hook up a new battery.

Our thoughts are that the engine is either getting too much air or that somehow the injectors aren't activating at start up. We did test this injector theory by switching the ignition relay, but that did not help either.

Other than that:
--the fuel lines are too narrow
--the engine has too much oil inside

If this post seems a bit mixed, then please let me know. I will be as clear as I possibly can.

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Location: Michigan, Lower Peninsula

Re: Mercury 115 FOURSTROKE Won't Start

Postby jimh » Fri Apr 13, 2018 5:29 pm

You mentioned that you "scanned" the engine, and I guess you mean you connected some sort of terminal to a port on the engine controller and were able to read data from the engine. On that basis I am going to assume that this engine is fairly modern and controls its operation with some sort of microprocessor controller. Usually modern engines have sensors that inform the controller about the engine block temperature and the air temperature. When the engine controller sees that the air is cold and the engine block in cold, the controller usually changes the fuel-air mixture during engine start to help the engine get started more easily.

If all of the above suppositions are true, then perhaps the reason this engine does not like to start when cold is caused by:

--bad temperature sensor for the engine block
--bad temperature sensor for the air

The determinant for starting seems to be whether or not engine block is warm. That seems to suggest that perhaps the engine temperature sensor is malfunctioning. Check to see it the temperature sensor is actually connected; maybe a lead fell off. (Of course, if the engine is really smart, it would tell you that the temperature sensor value was out of range, and the service manual would suggest what to do.)

Posts: 27
Joined: Fri Apr 13, 2018 1:25 pm

Re: Found a solution

Postby BWbert » Sun Apr 22, 2018 8:01 pm

Hi Jimh,

Thankyou for the reply.
We did take the temperature sensor into consideration, but it was functioning just fine.

We finally decided to scan the engine again as a last ditch effort.
After some testing, the engine wouldn't start at all and we also saw that the CPS sensor wasn't giving an rpm reading when cranking the engine.

What we assumed is that the CPS sensor was slowly dying throughout the past 2 weeks.
Please take note that it was also missing its cap which meant its copper core was exposed.

The engine is running fine now thankfully.