Is this a tank vent problem??

[DON-Z-26ZX]

I've been dealing with this same issue all summer long....99 454 mag mpi, some days it just runs absouletly perfect, then the next day I can be running & it will just fall off back to idle. The engine won't die, it will just drop back to idle, then stumble like it is running out of fuel. Sometimes I can let is sit for a min or two & all is good, however this past weekend it seemed to get worse. I've gone thru the entire fuel system, new regulator, pump, even the cooler is new, filter. I've replaced every sensor, except the TPS....it tested perfect. I've had the ECM reflashed, & of course a full tune-up, there are no codes. I've also checked all my grounds & they are tight & no corrision. There is just nothing consistent when it happens, I don't know when it happens, it just happens. It really doesn't make any sense at all to me, it goes against all troubleshooting methods.
One thing I have noticed, when fueling, & the tank gets close to full, I have fuel blow out the vent. I'm wondering if there is some fuel remaining in the vent line, & at times it will prevent the tank from venting properly.....I don't know if this is just a long shot, but I'm ready to try anyting. I contacted the tank manfacture & asked them about the pick up tube, I tried to remove it to check for any cracks, & I couldn't get it out all the way....they told me I can remove the screen off the bottom, & it will come right out, & it did....also, there is no anti-shipon valve.
I really am convinced that this is something "simple" I just have to find what "simple" is, it runs too good for this to be something major....

[MOP]

Simple test! Remove the gas cap then blow through the vent it should flow freely!

Phil

[mrfixxall]

I've been dealing with this same issue all summer long....99 454 mag mpi, some days it just runs absouletly perfect, then the next day I can be running & it will just fall off back to idle. The engine won't die, it will just drop back to idle, then stumble like it is running out of fuel. Sometimes I can let is sit for a min or two & all is good, however this past weekend it seemed to get worse. I've gone thru the entire fuel system, new regulator, pump, even the cooler is new, filter. I've replaced every sensor, except the TPS....it tested perfect. I've had the ECM reflashed, & of course a full tune-up, there are no codes. I've also checked all my grounds & they are tight & no corrision. There is just nothing consistent when it happens, I don't know when it happens, it just happens. It really doesn't make any sense at all to me, it goes against all troubleshooting methods.
One thing I have noticed, when fueling, & the tank gets close to full, I have fuel blow out the vent. I'm wondering if there is some fuel remaining in the vent line, & at times it will prevent the tank from venting properly.....I don't know if this is just a long shot, but I'm ready to try anyting. I contacted the tank manfacture & asked them about the pick up tube, I tried to remove it to check for any cracks, & I couldn't get it out all the way....they told me I can remove the screen off the bottom, & it will come right out, & it did....also, there is no anti-shipon valve.
I really am convinced that this is something "simple" I just have to find what "simple" is, it runs too good for this to be something major....

Have you omed out the injectors? ok heres what you do,,try to get at all the injectors you may have to remove the intake plenum...disconnect all the injectors and measure the resistance between the two treminals in the injector..i dont know what the resistance should be mabe around 12.8 omes,,if the injectors vary lets say 2 to 3 omes each then the lowest one iis bad....what will happed is the engine will run fine until it gets warm then the injector thats bad will over heat the quad driver in the pcm and shut down..do you have access at a scanner? read the map sensor readings, if it is below 128 HG at idle then its probably a bad injector..

also if you use cheep fuel filters ive seen the injectors get plugged with small paper particals..whyle you have the intake off and if the injectors are ok remove the whole fuel rail remove the clip that holds the injector to the rail and pull them out of the rail but watch the o ring on the end of the injector(somtimes they get stuck in the rail ) now look into the center of the injector where the fuel goes in the injector,,theirs a little screen in their that gets plugged with crap just take a can of carb spray and hose it out then blow the screen with some air pressure to make sure you got the screen clean..

[Forrest]

If your boat has a tank built by RDS, then most likely the fuel pickup has a screen. Moreover, if you have a fuel pickup screen then there is a good chance that it is clogged with trash. It doesn't take much trash to cause the condition that you describe.

Always get rid of the pickup screen and let the spin-on filter catch the trash. I would start there.