Logo
FULL SITE MENU

4.3 MPI - Won't run unless on auxilliary tank

D

darlington_john

Member
Ok, carryover from a previous thread. 2007 4.3 MPI 220hp that ran fine last year prior to winterizing. Started it this year and it ran fo 5 minutes and then cut out. Would restart but only a few times at rough idle and then die. I assumed it was either not getting fuel or there was water in fuel. So far I have done this to rule out bad fuel - ran the tank on an auxilliary tank where I tied it in to the system just before the fuel filter. Ran it for 0 - 15 minutes (on muffs) and it ran great.

Drained the main tank dry pumping out from the gas line which ties into the fuel filter. Reinstalled the gas line, put in 10 gallons of 89 mid-grade and started the engine again. It ran for 5 minutes (on muffs) and then started cutting out like it did before. Now I'm thinking that it is not getting any fuel from the main tank to the motor. Started lifting the floor to have a look at the tank - this boat has 50 hours on it. Looks clean.

So, it ran last year, now it doesn't on the main tank. Anti-siphon valve stuck???? I'm at a loss right now as it has to be the line from the tank to the filter. I can't see how it runs great on the auxilliary tank.
 
Check the main tank's vent line. Pull the anti-siphon valve and see if it's stuck...lube it w/WD-40 to get it loose.
 
i have had the fuel take the suction tube that screws into the tank and turn it into a rubbery tube that collapses on itself. bad fuel, the syphon valves stick, and its all fuel related, get corn liquor out of fuel.
 
Verified what was stated above with a local marine shop - they said the same thing. Anti-siphon valve or a collapsed tube. I can rule out the collapsed tube as I pumped the tank dry through the main line which comes out of the tank. Damn ethanol garbage.....
 
john, i would still pull the tube and inspect it, i pumped my tank with no problems, but as soon as it was running it would collapse, your pulling the anti syphon, why not pull the pickup tube as your right there and feel it.
 
Will do that - damn anti-siphon valve fitting broke off when I was taking it off the tank tonight. Guess I'll be picking up some PB Buster and get the fill line off the tank.
 
check for air leaks in the line somewhere, they can be very small, as for ethanol it has been in your fuels for over 10-15 years, and if fuel flows through your line to empty the tank it isn't the problem. not to mention that all your fuel hose manufactures have been making ethanol compatible hoses for years, and we used it as dry gas for 70 years.
 
chris, hate to tell ya but not in the concentration nor the chemical makeup that we are getting today, and any black hose made before 2008 i wouldnt trust with the crap there calling fuel today. if we had been getting gas like this for all this time, why havent we seen the breakdown of the inside of the rubber hose like we are seeing now, why are the needle and seats getting gummed with black flake, why is a rigid pickup tube turning to a flacid piece of crap?????????? you cant tell me this fuel is the same as what was 10 yrs ago, and you are using wood (rubbing) alch to dry out fuel, corn liquor should stay in my stomach not my gas tank.
 
check for air leaks in the line somewhere, they can be very small, as for ethanol it has been in your fuels for over 10-15 years, and if fuel flows through your line to empty the tank it isn't the problem. not to mention that all your fuel hose manufactures have been making ethanol compatible hoses for years, and we used it as dry gas for 70 years.
 
This is driving me nuts right now. So I changed out the anti-siphon valve and the fuel pickup line as well and it still won't run off the main tank. To date the fuel tank was pumped, a new filter was installed, and new fuel was added. All of the lines are original and they all look like new. I pulled the floor up to expose the entire tank and all the fittings all looked solid. Checked out the cap and it looked in good shape - no debris in the screen on the vent line either (or at fuel pickup). Put the portable tank back on and it ran perfect again. Switched back to the main tank and it died once all fuel that was in line ran out. Is it possible that the fuel pump doesn't have sufficient pressure to draw from the main tank?? There is 10 gallons of fuel in the tank currently - I wonder if I have one of those problem tanks that must be near full to run.
 
one thing left to try before you try a fuel pump. remove the line at the fuel sep and remove the line at the tank.
use a "catch can" and try blowing from the tank to the motor. then reverse the process and go from the engine to the tank.
I had one that you could blow air into the tank but not draw fuel. the hose was rotted internally and left a rubber flap to block the fuel flow.
 
entirely possible, what type of fuel pump do you have, and can you get the aux tank as low or lower than the main tank, as a way of testing the pickup ability of the pump
 
Bt Doctur - I pumped all of my fuel out of the tank through that line (connected a line to that line and used a primer bulb to draw all the fuel out) and that line is only about 2' long and looks in excellent condition. I also cut off about 3" from one end of the line when I installed the new AS valve and it was in great shape. I will pull it off and have a look to rule that out.

I believe that the fuel pump is electronic as it runs for a few seconds when the ignition is turned on. I couldn't get the auxilliary tank lower than the main tank as the fuel hose wasn't long enough to get me into the cuddy.
 
Had a few with blocked vent lines. This one is often overlooked. Spiders love to build nests in there. Back blow the vent line. OR to test for it, leave the gas cap off.Just for the test !!
Moondrifter
 
Back
Top