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2003 merc ob efi won't start when hot

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Beaubm01

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My 2003 motor starts right up and runs great. After shutting down and then trying to start an hour later, it starts, runs for a few seconds then begins to idle very rough and then shut down. If I wait a couple of hours it will start and run fine. I have found that if I remove the bottom of the water seperator and then reinstall it will start immediately 100% of the time without waiting for the cool down. Why would that cure the problem? Does that quickly release pressure on the fuel line? Is this vapor lock? Can this be caused by the fuel pump or the injectors? Any help would be appreciated.


ps...Ive replaced my fuel line with the bulb and the filter in the water seperator


Thanks in advance for the help
 
If you are running from a "built in tank" it could be a sticky anti-siphon valve on the tank itself (have seen your symptoms where that was the issue).

If you do have a built in tank try running off of a portable tank. If that cures the problem, replace the anti-siphon valve...
 
galamb said:
If you are running from a "built in tank" it could be a sticky anti-siphon valve on the tank itself (have seen your symptoms where that was the issue).

If you do have a built in tank try running off of a portable tank. If that cures the problem, replace the anti-siphon valve...
Click to expand...

Thanks for the response. Unfortunately, I am connected to a 6 Gallon Plastic tank with quick disconnect. Do those have anti-siphon valve?
 
Thanks for the response. Unfortunately, I am connected to a 6 Gallon Plastic tank with quick disconnect. Do those have anti-siphon valve?
 
No, no anti-siphon valve on a portable, just the tank vent - which is definitely open, correct?

What horsepower is the motor???
 
With no anti siphon valve on a portable tank and the vent screw open on the tank, the Mystery continues. The proble is obviously a fuel problem. I just don't understand what would cause the vapor lock and why removing the filter bowl would cure it. Something I did try was run the engine and then I removed the gas line from the engine before the hot soak. Before starting I rehooked the gas line. It still wouldn't start unless I removed the water seperator bowl. Looking for any helpful ideas....
 
Loosen the fill cap on the tank. That will tell you if the vent is plugged. Have you been running gasohol? Fuel lines may be swollen internally.
 
No gasahol...I removed the vent screw and made sure it was clear. Also already removed the gas cap and tried that. So to date I've:

1. Checked the vent on the tank and that was fine and clear.
2. Loosened the gas cap
3. Replaced the gas line and bulb ( cut the old one open and it was not deteriorated at all)
4. Checked the screen on the pick-up tube
5. Replace the filter in the water seperator
6. Disconnected the fuel line from the engine before the hot soak and reconnected just before starting.
7. Inspected the gas lines for any pinching, etc...

None of the above helped. I'm not that skilled of a mechanic, but not bad. Something appears to be either causing a vacuum that is broken when I loosen the water separator cup. Also, I did not mention this before but there is not much fuel in the seperator cup when I remove it. Should there be? I am really stumped.
 
I am going to throw a theory out there for ya, maybe someone else can share some experience here since I generally don't work on 4 strokes, particularly the EFI models.

Anyhow, as I understand the system on these, the high pressure fuel pump feeds your injectors, but any "left over" fuel is fed through the pressure regulator (part of the VST), then through the fuel cooler (since the temp increased when it was pressurized) and then it's scavenged back to be fed through again.

What if the pressure regulator is toast? I'm thinking it would leave a whole lot of pressurized fuel on the wrong side of the regulator (but not enough to fully feed the motor) and that could prevent the low pressure pump from getting sufficient fuel to the motor.

Again, don't work on these but sounds plausible - maybe??
 
galamb said:
I am going to throw a theory out there for ya, maybe someone else can share some experience here since I generally don't work on 4 strokes, particularly the EFI models.

Anyhow, as I understand the system on these, the high pressure fuel pump feeds your injectors, but any "left over" fuel is fed through the pressure regulator (part of the VST), then through the fuel cooler (since the temp increased when it was pressurized) and then it's scavenged back to be fed through again.

What if the pressure regulator is toast? I'm thinking it would leave a whole lot of pressurized fuel on the wrong side of the regulator (but not enough to fully feed the motor) and that could prevent the low pressure pump from getting sufficient fuel to the motor.

Again, don't work on these but sounds plausible - maybe??
Click to expand...

thanks for this suggestion. I see where the pressure regulator is. If I pull it out is there a way to test it?
 
graham, having similar problems with a friends 60 hp efi .where is the anti-siphon valve located on the tank. all i see is a tube for the pickup and the gauge sending unit. it's on a 2007 bass tracker
 
Read thread above. If it is a plastic portable tank there is no anti siphon. Make sure the vent is open and clear. Mine are fine but I'm still having the problem. I'm going take a look at
my pressure regulator when I can. Still looking for ideas.
 
dtoole - The anti-siphon is usually the "connector" between the tank itself and the fuel line (hose) on a built in tank. It often looks like a simple fitting (straight or L shaped) and, if functioning properly, will only let the fuel flow from tank to engine and not back the other way.

Beaubm01 - yes, the regulator can be tested. I have an excellent pdf file for complete testing of all aspects of the fuel system, including trouble shooting etc. Fire me an email [email protected] (make the subject EFI 40 - I sometimes get many emails and am getting old enough that I can't always keep track of all the requests :)) and I'll send it to you.
 
Thanks for the PDF. I've spent some time reading it and am working on borrowing a fuel pressure tester guage. Won't be back to the boat for a couple of weeks but will update when I have a chance to run through my checklist - mike
 
graham , could you post that pdf to the forum ? i am trying to understand the "workings " of the efi system . and how to troubleshoot .
 
Beaubm01 said:
My 2003 motor starts right up and runs great. After shutting down and then trying to start an hour later, it starts, runs for a few seconds then begins to idle very rough and then shut down. If I wait a couple of hours it will start and run fine. I have found that if I remove the bottom of the water seperator and then reinstall it will start immediately 100% of the time without waiting for the cool down. Why would that cure the problem? Does that quickly release pressure on the fuel line? Is this vapor lock? Can this be caused by the fuel pump or the injectors? Any help would be appreciated.


ps...Ive replaced my fuel line with the bulb and the filter in the water seperator


Thanks in advance for the help
Click to expand...

What was the solution to this?
 
beeze455 said:
What was the solution to this?
Click to expand...

I have a 2003 Mercury 60 Bigfoot engine as well. I go out to start it first time and it runs like a champ. Once it is warm and you shut it off, it fires, but as soon as you give it the gas, it dies.
The arrogant and expensive marina said it was the low pressure fuel pump. I purchased one and replaced it.. and it STILL does it. Any ideas?
Some say there is a screen on the bottom of the high pressure fuel pump that is clogged. But if that was the case, why would it run like a champ when cold?
Any ideas would be helpful.
 
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