Re: 1999 7.4 Mpi Vapor lock issue's
 

I am struggling with the same issue with my 7.4. Although I'm fighting 2 issues at the same time I think. One is the tendency to run hot thanks to the low water and amount of weeds in the lake. I sucked an impressive amount of seaweed into the system the other day and clogged the oil cooler off completely. I am planning to convert to a thru hull system over the winter this fall in order to hopefully mitigate this some. Running hot and heat soaking has caused it to vapor lock more than a few times when I let it heat soak. I'm going to try the check valve at the same time though. From other sources I've seen the reason we suffer from a vapor lock issue is the fuel rail is a dead head and once it is filled with vapor it has no where to go except through the injectors, which apparently struggle to purge it.

Re: 1999 7.4 Mpi Vapor lock issue's
 

Fuel injected will absolutely vapor lock. Ethanol SUCKS. It has a distinctly lower boiling point. I've been kicking around, besides the check valve, using a petcock valve like on an atv, to send vapors back to tank or to vent, so when locked, I set valve to easily vent vapors as close to injectors as possible away. Liquid doesn't compress, gas does. (Vapor) injectors like pressure to open, or in this case... Purge. Hope this makes sense. Fwiw. I'm a past refinery operator and dad is lab tech at same refinery for past 30ish years. Moral...ethanol SUCKS. O yeah, seafoam has helped, but not cured

Re: 1999 7.4 Mpi Vapor lock issue's
 

Best I can tell the problem is the fuel flows backwards toward fuel pump and settles in fuel cooler thus turning cooler into boiler. Hope this helps someone. Nothing worse than RUINING A SWEET BUZZ BECAUSE OF VAPOR LOCK! LOL!