1999 merc 225 efi back fire no start

[zx28]

I have a 1999 mercury 225 efi on a charger boat. I just recently rebuilt the motor because of two burnt pistons. I bored .030 over with new pistons and gaskets the usual "top end" rebuild. It still has the original crank and rods. I went to start today for the first time and it will hit once, twice, sometimes three times but won't fire up. It acts like it "wants" to start but it just cant quite "catch up". It backfires occasionally during cranking. It is getting spark and fuel to all cylinders. The spark is a little weak i guess but doesn't seem so weak it shouldn't crank. The plugs are ngk not the champion ql7cc or whatever the manual calls for. I am stumped and i dont know where to start to trouble shoot. Thank you in advance for your time and any advice you have.

 

[jerryjerry05]

Re: 1999 merc 225 efi back fire no start

First thing redo the compression test(for fun) then the spark with sparkies.
The fuel system.Get a fuel pump tester for the electric motor(you check for water)What's the reading? It needs to be within spec.You have a manual? If it's low or too high it will NOT run right.What's the serial #
Post your results.

Fill out the profile,you might be close to someone who can help.J

 

[zx28]

Re: 1999 merc 225 efi back fire no start

thanks for the info. I do have a manual but im not sure where to track down a fuel pump tester. The gas tank is half full and has been sitting outside in the weather for almost two months....before i bought it. I ve heard of ethanol "turning to water" or evaporating easily causing water in fuel. Can water in the gas cause the backfire. I guess the backfire worries me because on the efi tiiming is controlled by the ecu. I am going to try to get a tester and test my fuel pump. will post when i get some results. thanks and keep ideas coming please.

 

[zx28]

Re: 1999 merc 225 efi back fire no start

I checked fuel pump. Ive got about 35 psi at the check valve and i emptied the water seperator filter and filled it with fresh gas. Im pretty sure it is getting sufficient fuel and oil. Im afraid however that the weak spark im getting is causing the problem. Is there a way to determine if im right or not or what things may cause a weak spark. My manual says the stop circuit wire could be grounding out but ive inspected and it looks good to me. Any ideas

 

[jerryjerry05]

Re: 1999 merc 225 efi back fire no start

Spark tester.$6 at Auto Zone.Spark should measure 7/16"
Look at the stator for burned ends.It has 6 posts and sometimes one or more will burn..Check all connections.J