Losing fuelpressure
 

I have problem with my fuelpressure. I can run the engine for a while than the engine dies. Somtimes it´s hard to start again but it´s starts after a while. I messured the fuelpressure (on the fuelrail) while I was driving and just before the engine dies the pressure drops. I can hear both fuelpumps working but the pressure is bad. But after a while it´s back to normal. Whats wrong, where to start.
My engine is a 350 Magnum MPI -95

//Martin

Re: Losing fuelpressure
 

The first thing you need to figure out is whether the problem is in the engines fuel sysytem or the supply system. A ggod test for the suply system is a fuel vacumn test. install a T in the fuel line just before the fuel pump and attach a vacumn guase to it, it shouldn't go over about 2" of vacumn. If it does the first place to look is the anti siphon valves wich are right on the fuel tanks, it often just looks like a fitting but it has a check ball in it and they do get stuck. Actually the first thing I would do is check your water seperator and/or fuel filter. after you have eliminated the filters and supply sytem you can move on to the ehgine, does it hold pressure when the engine is not running ? cyvle the key switch to build pressure with the pressure guage on the rail. If the system leeks down you probably have a leaking injector, to find out wich one you can rpeform an injector balance test, but you will either need a scan tool or a home built precision timer box to do this. What you do is fire each injector for an exact amount of time and record how much pressure you lost, and see wich one is significantly diffrent. it is important not to preform the test more then once without starting the engine becuase you can put enough fuel into it to hydraloc it. If the problem is intermident another thing to check is the wring harness, with the engine ideling chake and wiggle the harness at the fuel pump and see if it stumbles, if so you probably just have a bad connector. Another common problem is for the screen in the inlet side of the pump to become clogged and block the pasage, boat builders love to use teflon tape on fuel lines and you are not suppost to do that, they make special sealers for fuel sytems. Hope this gets you going in the right direction.

Re: Losing fuelpressure
 

Hi
I try to lock into the anti siphon valves next time I go out to the boat.
The fuelfilters are new and the fuelpump is new but the VST is old and I have never cleaned it.
The engine keeps the pressure when it´s of.

//Martin

Re: Losing fuelpressure
 

If it has a VST and you have never cleaned it that's where to look. pull the cover off and you will find a screen filter in there that likes to get plugged. They should be serviced every 100hrs or once a year. The filter is pretty spendy for what i is I think like 70 dollars or something and you will need a new seal for the cover. When you install the new oring seal you need to glue it in with somehing otherwise it pops of it grove.