Hi, I tuned my fuel pressure regulator for my holley blue to 6 spi when the car is off. When I turn the car on, the fuel pressure shoots up to 12 but the car still runs normal... What's going on, and is it fine to leave it?
Fuel pressure will vary depending on tempature and altitude. Don't expect it to stay right where you set it running or not. Once the pump heats up the pressure will drop some too. It is not only Holley pumps that do that. However, if you are using a Holley regulator I suggest you ditch it ASAP they are typically not very good. I much prefer the Mallory regulators (BG's are good too).
He is saying that when the engine is off, the fuel pressure is 6 psi, and when he starts it the fuel pressure goes up to 12 psi.
That doesn't make a lot of sense since when the engine is off it will build pressure but when it is running it will bleed of pressure due to the engine's fuel consumption. I do agree with the thought on irregularities...but 6 psi positive?
Well when the engine is not running you do not have the alternator charging (increasing) the voltage, this could have something to do with why he is seeing a lower pressure when the engine is not running. You should always adjust the fuel pressure with the engine running.