Glad someone else caught that. I thought I was seeing things for a moment.
Burning Smell on Acceleration.
- Thread starter teach
- Start date
Glad someone else caught that. I thought I was seeing things for a moment.
" air release valve lets air purge until fuel reaches it then closes"
Not quite... it's just a spring and ball, and the spring sets the fuel pressure by pushing the ball into a passage in the filter head. There's no way for the ball to seal against the brass return line nipple with the stock spring... the compressed height of the spring holds the ball about 1/8" away from the back of the brass fitting. The only direction it can seal is with the spring pushing the ball toward the filter head.
Pure and simple, it's a pressure valve meant to regulate the fuel pressure. However, as those springs age they stop sealing the ball properly. They rely on basic physics to vent air... since air compresses, unlike fluids, it builds pressure rapidly when fuel is flowing into the filter. Since the air compresses and exceeds the springs hold, and it's above the fuel, it's just naturally the first thing to leave the filter housing.
This was tested and verified with a fuel pressure gauge and different springs. No spring, ball sealed to brass fitting immediately, trapping air. Stock spring, 0-~.5 psi of fuel pressure, rest of the fuel was being sent to the return line (path of least resistance) and wasn't supplying the IP with enough. Pilot G-2 spring, 5 psi after initial spike of air pressure left.
Not quite... it's just a spring and ball, and the spring sets the fuel pressure by pushing the ball into a passage in the filter head. There's no way for the ball to seal against the brass return line nipple with the stock spring... the compressed height of the spring holds the ball about 1/8" away from the back of the brass fitting. The only direction it can seal is with the spring pushing the ball toward the filter head.
Pure and simple, it's a pressure valve meant to regulate the fuel pressure. However, as those springs age they stop sealing the ball properly. They rely on basic physics to vent air... since air compresses, unlike fluids, it builds pressure rapidly when fuel is flowing into the filter. Since the air compresses and exceeds the springs hold, and it's above the fuel, it's just naturally the first thing to leave the filter housing.
This was tested and verified with a fuel pressure gauge and different springs. No spring, ball sealed to brass fitting immediately, trapping air. Stock spring, 0-~.5 psi of fuel pressure, rest of the fuel was being sent to the return line (path of least resistance) and wasn't supplying the IP with enough. Pilot G-2 spring, 5 psi after initial spike of air pressure left.
Last edited:
Similar threads
