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454 mag mpi fuel system
i have a 454 mag mpi that I built 10 yrs ago and removed the vst tank and ran a fuel cooler... I have never had fuel pressure of 34lbs at the rail and it’s never been a problem because the boat is very light. Now I’m upgrading to a little bigger boat and want to get the system right but nobody really seems to know what to do. Here is a picture that drew of my set up... the gas returning to fuel tank is a lot of volume and increase with throttle increase... can I remove the return line from the rail and just plug it, since I have a return to the fuel filter/water separator from the regulator on the fuel cooler? I have though about trying to kink a line and checking the pressure but the return from fuel rail is a spliced line and don’t want it to blow close to hot exhaust. Im running a green color regulator... I should have 38lbs at min and 42-43lbs max... please any help would be great. https://cimg2.ibsrv.net/gimg/www.off...4031bb362.jpeg |
I don't know anything about the factory fuel system, I can't see how you would have any pressure at the rail with that set up. Normally you see the regulator at the end of the rail to build pressure and a return line out of it to regulate the pressure.
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As I see it, you took the VST return to VST tank and have it going return to baot tank. The cool fuel over pressure gets returned to filter.
I would have done it different, but using your design, your issue is the regulator in front of the rail. Fuel comes in one tube to supply injectors and any over pressure is released by the regulator (used as a damper on VST) and goes back to the tank. So you need a regulator which will keep the pressure as set |
It has the dampener regulator on the rail which has no return. There is also no vst tank. This is basically stick set up with vst tank removed... on non vst style cool fuel systems they do not have the return line from the rail, that why I was asking if I should plug it... |
I'm just looking at your drawing, and hope you have the vacuum line attached to the reg
https://cimg3.ibsrv.net/gimg/www.off...488b5870e7.jpg Now if your asking can the rail be plugged and just use the cool fuel module, then I would say yes, and it should work https://cimg4.ibsrv.net/gimg/www.off...a0fd41080e.jpg |
For what you are trying to do, yes plug the 'out' from injectors.
I also have to say, I don't like injectors dead headed. I know some engines come this way, but fuel volume available to inectors will be down a little and if air is present it has to go thru them vs maybe going to tank instead. I would plumb the high psi pump to the'in' of fuel rail and then the fuel rail 'out' to the fuel cooler, fuel cooler regulator can then go to an in of the filter/separator or to the tank. |
Thanks I’ll see how I can plumb it, will need hoses and fitting made to redo it that way, and I know the regulator should be after the system, just very strange how merc did it their way also... gonna try to plug the rail return line first and see what gauges shows... do they make and adjustable one for the fuel cooler? Thanks again.. |
I would be concerned abt the fuel getting hot in the inj fuel lines with no return to keep fuel moving. Injs would probably create enough flow when running but when eng was shut off I bet the fuel would boil (vapor lock) and make re-starting after a short heat-soak period difficult.
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Agree the vst and cool fuel and all the other Merc systems don't return to tank, so VL is a concern. Mine was a vst and changed to cool fuel during repower. The line which returned to vst tank, was moved to return to fuel tank. The regulator on the rail controls the pressure
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You seem to know about these MPIs,
Does GM have a replacement for the fuel regulator on the end of the fuel rail like some of the other sensors on the 7.4 LX MPI?? Thanks |
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