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blgiles78
05-25-2007, 07:08 PM
I just replaced my fuel pressure regulator on my Maristar. It is a TBI unit and the regulator is built into the throttle body. It is a simple spring loaded diaphragm without any vaccuum lines. I replaced it because the engine is not maintaining fuel pressure. When the key is turned on the old reg. would allow the pump to go up to 22 psi and then when the fuel pump stops the pressure will immediately fall to zero. I replaced it with a new one from Indmar and now it is worse. It will only get about 10 psi and it will not hold fuel pressure at all. I took off the regulator and I was able to blow air through it with my mouth. I believe they sold me the wrong regulator or it is bad.

I can kink the rubber return line and my fuel pump will easily pump up to 40 or 50 psi and it will hold fuel pressure until I unkink the line. So, It has got to be a regulator problem right? This test should show that the check valve in the pump is good and the pump has enough pressure right? It is a brand new fuel pump on the engine.

Should I be able to blow air through the regulator with my mouth! It should not open until 30psi!

blgiles78
05-25-2007, 11:43 PM
Does anyone know what the fuel pressure should be on a TBI injected Indmar 5.7L with 265HP. Indmar says 30psi and Mastercraft says 12psi. Who is right? How long should the pressure be maintained after the pump stops running? Will this loss of pressure after key on cause problems?

I took my old regulator apart and inserted a small nut in it to increase the spring pressure. It got the fuel pressure up to 35psi. It still will not hold pressure when the pump stops. So, I know my pump is producing plenty of fuel, it was just running right through the new regulator.