Fuel pump issue
Thread Starter
Racer
Joined: Feb 2010
Posts: 365
Likes: 57
From: south wilmington il.
Fuel pump issue
I've posted this before and got no answers, my 95 vortech supercharged lt 1 fuel pumps both stay running for up to 6 seconds after the key is off. The car runs fine but when I shut it off my fuel pressure goes to zero, electric guage, but if I turn the key on again it goes to 40 psi. The in tank pump I believe powers the t rex pump. I'm thinking the fuel pump in the tank has to be replaced, due to faulty check valve. I also have an AEM adjustable regulator. I'm ordering a 340 lph in tank pump from aeromotive and removing the t rex altogether. Someone said my oil pressure switch could be keeping the power on after ignition is off, how should check that? Also does anyone know what and where all the relays are for the fuel pump, what number relay I should order. I think it's under the pass side dash,just want to make sure there isn't another one hidden somewhere. It's 10 degrees here and I want buy everything I need to do it in one day. Thanks.
Safety Car
Joined: Aug 2009
Posts: 3,745
Likes: 275
From: Melbourne, Victoria, Australia
I've posted this before and got no answers, my 95 vortech supercharged lt 1 fuel pumps both stay running for up to 6 seconds after the key is off. The car runs fine but when I shut it off my fuel pressure goes to zero, electric guage, but if I turn the key on again it goes to 40 psi. The in tank pump I believe powers the t rex pump. I'm thinking the fuel pump in the tank has to be replaced, due to faulty check valve. I also have an AEM adjustable regulator. I'm ordering a 340 lph in tank pump from aeromotive and removing the t rex altogether. Someone said my oil pressure switch could be keeping the power on after ignition is off, how should check that? Also does anyone know what and where all the relays are for the fuel pump, what number relay I should order. I think it's under the pass side dash,just want to make sure there isn't another one hidden somewhere. It's 10 degrees here and I want buy everything I need to do it in one day. Thanks.
The usual problems are leaking injectors, check oil for gas smell. Or the plastic fuel pump "pulsator" that fits between in tank fuel line to fuel pump, most replace this with a rubber hose and hose clamps if its leaking. Otherwise fuel pump could be not holding pressure.
Don't forget the fuel pressure regulator, if the diaphragm in the regulator has split it can leak fuel via the vacuum hose into engine ... Again smell the oil for gas smell, any oil dilution can be a problem. even though gas will go from liquid to vapor very quickly a lot will cause oil dilution problems so keep an eye on oil pressure.
In regards to the pump staying running for a few seconds after shutting engine off is not normal, would have to confirm via wiring diagram however the oil pressure is used as an indictor the engine is running to allow fuel relay to energize. However when ignition is switched off the fuel pump should stop right away, some early years also use the ignition reference to enable fuel however this is just from memory.
In short the fuel pressure dropping over minutes or hours would not worry me, if its instant a lot of fuel pressure loss quickly would mean its going into the engine if injectors not holding the pressure would go into the oil via gravity.
Good luck
