85 engine electrical.pdf - Vintage Snow

ENGINE ELECTRICALEFI Fuel System Maintenance and TestingThe regulator can also vary pressure consistent withengine load, atmospheric pressure, etc. A manifoldpressure tube runs between the mag end throttle bodyand the top of the diaphragm. As the throttle isopened, the pressure in the throttle bore rises. Thisadditional pressure enters the cavity above thediaphragm, assisting the regulator spring and raisingthe pressure in the rail, allowing more fuel through theinjectors while they are open due to the higherpressure. The opposite is true during deceleration.High engine vacuum while the butterflies are closed isapplied to the top of the diaphragm, allowing the fuel tocompress the spring and open the regulator valve at alower pressure. These pressure changes are verysmall and tend only to maintain a specific pressuredifferential between the throttle bores and the fuel rail,and not to vary mixture ratios while driving.FuelIn addition to checks made under fuel pump service,the pressure regulator span can also be checked.With a fuel pressure gauge on the fuel line and aMity-Vac pump (PN 2870975) installed on theregulator, activate the system the same as was donefor the fuel pump check. The fuel pressure atatmospheric pressure should read between 35 and 37psi; with five inches of vacuum it should be between33 and 35 psi; with ten inches of vacuum it should readbetween 30 and 32 psi; and with five pounds ofpressure it should be between 42 and 44 psi.Consistent readings outside the span indicate a badregulator, bad hoses or filter, bad fuel pump, or aninaccurate test gauge. Verify the problem and correctit before any additional work is done to the system.InjectorThe injector is an extremely close tolerance solenoidtype valve which opens and closes electrically. Itallows fuel to pass from the fuel rail through theinjector body and into the throttle body. The quantityof fuel is controlled by the length of time each injectoris open, and constant fuel rail pressure.Filter8/94 4.46