Merc 3.0 Vapor Lock

[searay_89]

Hi,<br />I have the following setup:<br />1989 Mercruiser 3.0L<br />Pertronix ignition<br />new (last season): carb, wires, coil, dist. cap, fuel filters, fuel line.<br /><br />I'm experiencing vapor lock after 45min to 1hr of operation. Can limp in but will not start if I shut it down. After cooling, boat starts and runs fine - dies after 45min again. This is clearly vapor lock to me. Different brands of fuel seem t impact this time somewhat. Running blower all the time seems to help a bit. Is there anything that I can add to the fuel to raise the fuel vaporization temperature?<br />A way to insultate the fuel line?<br />Other options?<br /><br />Thanks

 

[DaveM]

Re: Merc 3.0 Vapor Lock

You might try putting a bag of ice on the fuel line to confirm whether or not it is really vapor lock. The reason I say this is I once had an anti-siphon valve that would shut closed after the engine warmed up. Years later I had a fuel pump with corroded connectors that would fail after the engine was warm.

 

[searay_89]

Re: Merc 3.0 Vapor Lock

Thanks Juan -<br />But the fuel pump is mechanical - not electric, not even sure what the anti-siphon valve is or where it's located. I've changed everything (fuel and ignition) and this problem remains a constant. I never had this problem when I lived in Texas - now in the Northeast I've experienced it the last several seasons. I'm thinking that the gas companies are changing the fuel makeup - maybe adding more alcohol - and this creates the problem.

 

[vipzach]

Re: Merc 3.0 Vapor Lock

The anti-syphon valve is on the gas tank. The little fitting that screws into the elbow, where the fuel pump is fed from. If you look in it, you can see a little ball.

 

[tommays]

Re: Merc 3.0 Vapor Lock

i would be looking for a clog in the vent line to the tank you can open your filler neck cap and see if this clears it up<br /><br />instead of guessing you can tee in a vacume guage on the fuel pump inlet and see whats going on theres a spec here some were but if you start drawing more than 5in or so thats bad<br /><br />vapor lock usally only happens when you shut down and sit<br /><br />tommays

 

[searay_89]

Re: Merc 3.0 Vapor Lock

Thanks everyone -<br />Obviously much knowledge on this board - and that's why I'm here. The vent is clear and loosening the filler cap does not help. I did check the anti-siphon valve a couple of seasons back and it was clean and working - but I'll look at it again. Never thought this valve could have a thermal problem? I've engineered this problem to death and if I have to use brand A gas as opposed to brand X or Z then that's what I'll do - we have a short boating season here and with limited free time - I'd rather boat than chase this mysterious problem.

 

[tommays]

Re: Merc 3.0 Vapor Lock

are you sure you have spark when the motor dies ? many problems only happen when the motors hot<br /><br /><br />its not likely to be the gas<br /><br /><br />if you test vacume on the intake side and pressure on the outlet side you should find your problem<br /><br /><br />tommays

 

[ss9940]

Re: Merc 3.0 Vapor Lock

I had a similar problem... found out that i had no spark after shutting down - otherwise the engine would run great. The problem was the cable that is going from the distributor electronic module (assuming you have an EST ignition) to the ignition coil - there is a resistor integrated into that wire. After the engine got hot, the connection was gone - and the spark also. Found the error with an ohmmeter. Just a possibility you can easily check.

 

[searay_89]

Re: Merc 3.0 Vapor Lock

Complete history:<br /><br />Started having problems - replaced ignition with solid state - still there.<br />Checked fuel line , filters, replaced fuel pump diaphram - still there.<br />Replaced carb and fuel line - still problems.<br />Replaced coil, wires, cap - even went back to points & condenser - still problems.<br /><br />Several refuels in this process - all with the same brand.<br /><br />Filled up with EXXON instead of HESS - ran for 2 days without problem.<br /><br />Season over.<br /><br />This season - new alternator and battery - old alt was bad for a while. Running perfect.<br /><br />Filled up with EXXON. Problems come back on first day after 3/4 hour, but with cool down periods, still use most of new gas throughout the day.<br /><br />Fill up with SUNOCO on second day. Ran perfect all day - no hard starts no bogg under load. Ambient temp was higher on the second day.<br /><br />Not sure I can come to another conclusion except there is a problem with certains fuels and my system.