fuel pressure problem?

[mikec]

The factory fuel pressure regulator is referenced to THROTTLE BODY air pressure - not INTAKE MANIFOLD PRESSURE/VACUUM. The little "L" shaped vac hose on the factory setup sees boost pressure or atmospheric pressure; it never sees engine vacuum because it taps into the system BEFORE the throttle plates. When installing an aftermarket fuel pressure regulator, you want to use that same port - you don't want to feed vacuum info to the regulator.

 

The idea is this:

The fuel pressure regulators need a specific fuel pressure to get a good spray pattern and to flow a given amount of fuel for each millisecond they're ON. The fuel pressure has to "fight" whatever air pressure exists at the spray tips of the injectors. For StarQuest throttle body setups, the injectors see only atmospheric pressure or boost pressure... so that's all the regulator should "see" as well. That way, the injectors ALWAYS have 36psi high fuel pressure going into them compared to the air pressure they're spraying into.

 

Multi-port cars, with the injectors AFTER the throttle plates, have the injectors spraying into intake manifold vacuum or boost... so they have fuel pressure regulators tied into manifold vacuum.

 

On a StarQuest, the fuel pressure should NEVER be below 36psi: idling, driving around town, decelerating from high speed with your foot off the gas, etc. The pressure should RISE above 36psi though as boost pressure builds. The stock ECU expects this - and so do the stock style injectors. Factory fuel pressure regulator or aftermarket... doesn't matter.

 

mike c.