Fuel Pressure Holding ?

[TurboTdr3.8]

How long does the fuel pressure hold after you cut the car off , other than injectors leaking what would cause fuel pressure to bleed off , mine stays up for maybe 10 minutes or so and then it goes slowly to zero , Does this sound normal . It primes back up when restarting and starts perfect , I checked my old fpr under vacuum and pressure against a new one and they do the same readings . BTW I have found no leaks in the line or hoses either . It this a sign of a weak fuel pump or relieve valve ? Or should I not worry about it .

 

[ijames]

The pressure should hold over 20 psi for an hour or two, but so long as it's not an injector or hose leaking through it really isn't that big of a deal. The pressure can bleed off back through the check valve in the fuel pump, through the fuel pressure regulator into the return line, through a leak in the fuel pressue diaphragm into the vacuum line, through a leak in a hose, or through an injector. Some day when you have some time and the engine is cold turn the key on for two seconds and then off to prime it up, wait for the pressure to drop to zero, do it a couple more times, then pull the spark plugs and make sure they are all dry. If one is wet, that injector is leaking and you are putting gasoline into the oil and washing the oil off of the walls of that cylinder so it is dry on each startup. If two fuel pressure regulators do the same thing on your car it is most likely not the reg, and I'm assuming you would notice a hose weeping gasoline. So it's either an injector or the pump check valve. Some old school Bosch external pumps from back in the day before good in tank pumps were available didn't even have a check valve and it didn't seem to hurt anything.

 

[earlbrown]

If you have a pulsator in there it can leak like hell. Along with the short fuel hose if it's not the correct J30R10 hose that's rated for submurtion.

 

[TurboTdr3.8]

Along with the short fuel hose

earlbrown is the hose you are referring the one that connects the fuel pump to the holder ?

 

[Shawn N]

The stock pump has the pulsator and most aftermarket pumps like the Walbro 340 use a short hose instead. Like Earl said if the hose is not the correct rated one it will turn to goo.

 

[earlbrown]

earlbrown is the hose you are referring the one that connects the fuel pump to the holder ?

Yes. Tossing that pulsator gets rid of two leaks. The hose that replaces it HAS to be both hi pressure FI hose AND rated for submertion.

 

[pacecarta]

10 minutes ...I wouldnt be concerned

if it dropped in seconds i would want to know why

if your rubber lines are in good shape they wont swell and it wont take much leakage to drop the pressure , just a few drops of liquid is all it takes

if you clamp the rubber return line closed either at engine by frame or above axle (1/4" line) and pressure drops you have a leak on pressure side , it could be external leakage like an injector oring or a line fitting or hose clamp is loose or it could be internal like the the injectors , the line in tank or the fuel pump check valve is leaking.

if pressure holds the regulator is leaking ..that doesnt mean its defective just that thats where its bleeding down.

 

[S10xGN]

Mine drops in seconds, it's due to being over-zealous while porting my Accufab regulator (after adding an Aero340 fuel pump). Anytime you alter a part, there's a good chance it will do something unexpected. It's not a problem, and only takes an extra second during start-up to build pressure...

 

[87GNSteve]

Not really on subject but I was really impressed when I cut into the rubber fuel lines at the junk yard on a 3.8 FWD 85 Electra and it still had a lot of pressure. Had an aftermarket FPR on it too.