Fuel Pressure Bleedoff
 

Hi All,

I am helping a friend install prochargers on his 496 HO motors and have a question. The chargers are installed & fuel pressure is @50 psi with the key on (good thing) but when the key is shut off the port engine goes to 0 psi but the starboard stays @ 50. We switched the gauges to make sure & got the same result. No fuel leaks & when power is on there is not a problem just a minor annoyance. I have been told that the EFI motors should hold the pressure when the pump is turned off. Any ideas? Thanks in advance. Russ

Yes you are correct fuel sytem should hold pessure as your port engine dose.
The easy and obvious is to check all fittings. I've had problems with the o-rings getting chewed up while tighning up fittings . good luck

No fuel leaks. I just can't figure out why it bleeds off.

It's probably just the rotary vane pump. My pump use to hold pressure for day. Now it's gone as soon as I shut it off and turn the key back on. I haven't had any detrimental effects from it however. Sounds like the regulator is doing it's job.
Dave

Thanks for the input Dave

There can be leakage in the injector/s. The only way I know to check for this is to pull them and have them bench tested. A commom symptom of this is engine wont fire on the first turn of the key.

Yes, you can have a internal injector leak. I don't think these engines have a return regulator, but that also would be something to check. As a side note, always keep an eye on the injectors. If one starts to lay down, you'll burn a piston. It's a shame to ruin a good engine because of a bad injector.

:rolleyes: Just as a suggestion, search for "It's for certain....Meltdown" in Q & A. There is a lot of P.C. info in it as well as critical info about Aeromotive fuel pumps & use of regulators, mounting, routinf of hose, etc. It may save you an engine someday....(soon). The ECM controls the pumps on & off. It energizes a relay for the external pumps. The fuel pressure may bleed down with the engine switch off, but so what? you want pressure up & holding with the key ON!! The excess pressure is being bled back to the tank, unless you are using a cool fuel/VST/or other set up where it is returned back to the pressure side of the pump. This is not necessarily a good thing as it adds heat to the fuel that may or not be removed by the cooler. It will certainly add to the possibility of fuel boiling in the lines (not due to 200+ temps though) & vapor lock. Search for a LOT of P.C. info on the board....there is a great deal available. .....
:D

Thanks for the help guys.

Russ

HP500, Did your buddy install adjustable regulators like Vortec? If so, and the diaphram has a hole or he forgot to install the spring, then that will cause this problem. If he hasn't installed one then it could be just a bad pressure regulator.
It could be other things, but I had this problem last spring so I know it will cause this problem.;)

The 496 motors can be tested with the scanning tool. The fuel rail pressure can be pumped up and then each injector tested/fired with the scan tool, noting fuel pressure drop. It is really a cool test! You should have a dealer do the test for you it may really help!
Sincerely
Dennis Moore
FAMILY AND PERFORMANCE BOATING MAGAZINE