1999 Mercruiser 4.3 mcm gas issues?

[endurance]

Hi Guys, this motor Sat for 7 years. The injectors were bad. Had them serviced now there spraying ok. The fuel pump is working at start up and the motor runs on muffs. Took the BOAT out on the water. It starts and runs for a minute or so then dies out. Then if I try to start it right away.it won't start then if I wait a minute it starts and repeats the same process. Got it back home started it back up
ran for a bit. Rev it up responded normal. Bought it back to idle. 600-700rpm. Thing is when it idles it fluctuates it's not a constant steady idle. So I removed the spark Aresstor spray pattern was fine. Turned it off. Tried to start it and no fuel came out of the injectors. But every time I turned the key I could hear the fuel pump. So I thought the fuel/water separator might be empty removed it and it was half full. The pump previously had a lot of pressure going into the throttle body. I found that out by disconnecting the fuel line to the throttle body. That's how I discovered the injectors were
clogged. So need help in determining 1) why at idle it raises and drops. Why it ran on muffs continually but on the water stalls out. Any ideas in the right direction would be greatly appreciated.! Oh by the way one cylinder has low compression compared to the others. Thanks in advance for all your help I appreciate it

 

[Scott Danforth]

did you completely drain the goo that was left after 7 years and clean the tank and lines?

 

[alldodge]

I'm thinking fuel pump pressure issue or antisiphon valve.

When the boat sits on the trailer its at a different angle then in the water

 

[endurance]

Thanks for the response. You lost me on antisiphon valve what does it do and where is it located. In
regards to the fuel lines, from the water separator to the fuel pump I did not clean. But did run seafom and gas through the tank and pump out several times

 

[endurance]

Question at idle rpms go up and down fluctuates.
between 600- 700 rpm. When it gets closer to 600 rpms it starts to stall and then the motor stays on and goes back up to 700 rpm. Then the cycle. Repeats. Then when I give it throttle to about 1500-2000 rpm it runs smoothly.

 

[endurance]

in regards to cleaning the 7 year goo build up. When I disconnected the fuel line at the throttle body gas was free from any goo. I used a separate fuel container. To cycle gas through the new water/fuel separator and fuel pump

 

[endurance]

Could it be the oil pressure switch that sends the power to the fuel pump going bad. Guess I'm looking for other things to check to solve the problem thanks Guys for all of your input Greatly appreciated!

 

[endurance]

AllDodge how do you check the fuel pressure on the pump thanks for your input I appreciate it

 

[alldodge]

If the gas was 7 years old, filtering it will not make it good, but would get the goo out. If you just added more clean gas after filtering then you have a mess, just a cleaner one.

The antisiphon valve is connected to the fuel take and the fuel line connects to it. It looks like a barbed fitting but inside is a spring and ball. This is a check valve to keep gas from siphoning if the fuel line cracks/breaks.

The up/down idle issue can be from the gas and also from the IAC (Idle Air Control item 7) valve. This is part of the throttle body and can be removed and cleaned, but don't use carb cleaner or other harsh chemicals. Note the condition of the O ring.

http://www.mercruiserparts.com/bam/subassembly/31496/2692/170

 

[Scott Danforth]

you cant fix fuel that is a year old, much less 7 years old.

as SD pointed out, filtering only keeps out the chunky stuff. it cant rejuvenate fuel that has long since broken down.

drain the mess you have and go thru your entire fuel system.

 

[endurance]

Thanks Guys I appreciate all your input I failed to mention the tank was empty and had no gas in it prior to me adding fuel and seafoam mixture and cycling thru. AllDodge thanks for the heads up on the iac and the anti siphon much appreciated. Will check and post

 

[endurance]

AllDodge what do you recommend to clean the iac

 

[alldodge]

AllDodge what do you recommend to clean the iac

Remove, clean the tip and spring pf the IAC and the tip seat in the throttle body.

 

[endurance]

Thanks

 

[endurance]

AllDodge appreciate it will let you know how turns out