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2003 Mercury optimax 250 won't start

J

jstrickland28

New member
optimax 250 jet drive serial number: 0E416021 Turns over and fires but won't run. Checked air (80 psi) and fuel (90 psi) pressures. Replaced all three diaphrams on fuel rails. New high and low pressure fuel pump. New float and needle in vst and cleaned it out (didnt find any gunk or anything). New TSP and ignition switch. New merc spark plugs and checked with an inline spark plug checker that turns a light on when firing spark. I know this isn't the best way to test coils and spark plugs but its what I had. I also have fesh fuel. I have vessel view and it isn't throwing any faults. I hear all fuel pumps running when key on. Fully charged batteries 850 ccamps All mechanics in my area won't be able to look at it till October. Any other suggestions??? PLEASE HELP. Take it easy its my first post. I read through alot of threads to get to this point
 
yes sir. I worked on it a little more today and decided to start over so I pulled the new spark plugs out. I had 3 spark plugs that were covered in carbon and oil. They were wet when I pulled them out. I cleaned them and checked the gap on them and re installed. The motor fired up on the first crank. It idled great and I turned it over several times with the same result. Then about the 10 th time I went back to not starting until about the 8th crank. I haven't pulled the plugs again to see if they have fouled or whatever you would call it. The port side all had really gunked up plugs the starboard side were all clean.
 
Sounds like you need to pull the injectors, all 12 and have them professionally serviced. With out a scan tool it is hard to test the injectors. My money is on a stuck or dirty direct injectors. Other things to check are the reed valves.... And the reed plate in the compressor.
 
Would the clean plugs on the starboard side that looked normal have any issues with the injectors? I get that sending all of them in f or service is best option im just curious. The bank on the port side is where all the fouling was happening.
 
Questions.... When you hooked the fuel pressure gauge to the rail (assuming you have a non liquid filled mechanical gauge) did the needle jump back and forth rapidly between 80 & 100 PSI or was it rock steady at 90 PSI?

Cleaning the injectors is an important service on an Optimax. The direct(air) injectors are now North of $500 each. A stuck/clogged Direct injector will cause hard starting and idle issues along with fouled plugs.

Broken/missing reed valves will cause stall issues and rough idle. You can hear a broken reed if you listen close, You can also watch the intake air temp rise if you have diagnostic scan tool.

Broken Reed plate in the compressor will cause a stall condition.
 
Your are correct I am not using liquid filled gauges. The needle did bounce between 90 and 100. Is that because its not liquid filled? I will check the reeds tomorrow afternoon and let you know. Thank for the reply.
 
Should the fuel pressure maintain 90 when off? Both pressures seem to fall to around 60 and 50 after cranking. Every now and then the fuel pressurr will hold at 90 after cranking.
 
jstrickland28 said:
Your are correct I am not using liquid filled gauges. The needle did bounce between 90 and 100. Is that because its not liquid filled? I will check the reeds tomorrow afternoon and let you know. Thank for the reply.
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Both pressures will drop after shut down or when cranking is stopped.

Look at your gauge again, a non liquid filled gauge will bounce between 80 and 100 psi on a 90psi system not 90 and 100. Pull the injectors and take them for service. Check all reeds, change the plugs.

Make sure you red loctite all screws on the fuel rails.
 
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