90-823225--1 10965E-70 - ELECTRONIC FUEL INJECTION (MULTI-PORT AND THROTTLE BODY)
Throttle Body Injection Fuel System Diagnosis (Continued)
Chart A-7 (3 of 6)
SHUT-OFF TOOL
WATER SEPARATING
FUEL FILTER
RETURN LINE FROM FUEL
PRESSURE REGULATOR
IMPORTANT: Check for contaminated fuel tank,
stuck anti-siphon valve or fuel system vacuum
leak anywhere before the electrical fuel pump
and after the fuel pressure regulator.
TEST DESCRIPTION:
Number(s) below refer to circled number(s) on the
diagnostic chart.
1. Pressure less than 28 PSI (193 kPa) falls into two
areas:
• Regulated pressure less than 28 PSI (193 kPa).
The system will be running lean. Also, hard start-
ing when cold and overall poor performance will
be noticed.
• Restricted flow causing pressure drop. Normally,
an engine with a fuel pressure of less than 24 PSI
(165 kPa) at idle will not be driveable. However,
if the pressure drop occurs only while underway,
the engine will surge then stop running as pres-
sure begins to drop rapidly. This is most likely
caused by a restricted fuel line or plugged water
separating fuel filter.
2. Restricting the fuel return line (Shut-Off Valve) al-
lows the fuel pressure to build above regulated
pressure. With battery voltage applied to the fuel
pump, pressure should rise to 60 PSI (414 kPa)
as the fuel return hose is shut off with special tool.
NOTE: Do not allow fuel pressure to exceed 60 PSI
(414 kPa); damage to the pressure regulator may re-
sult.
3. This test determines if the high fuel pressure is
due to a restricted fuel return line or a pressure
regulator problem.
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