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5B.41
Section 5B
EFI Fuel System
5B
Diagnostic Aid #5 “FUEL PUMP” (fuel pump not
turning on)
Possible causes:
1. Fuel pump fuse
2. Fuel pump circuit problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Circuits
30, 87, and relay.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Circuits
30, 87, and relay.
3. Fuel pump
Diagnostic Aid #6 “RELAY” (relay not operating)
Possible causes:
1. Safety switches/circuit(s) problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Circuit 3.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Circuit 25.
2. Relay circuit(s) problem
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Circuits
18, 85, 30, and 87.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Circuits
28,85, 30, and 87.
3. Relay
4. ECU grounds
5. ECU
Diagnostic Aid #7 “IGNITION SYSTEM” (no spark)
Possible causes:
1. Spark plug
2. Plug wire
3. Coil
4. Coil circuit(s)
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Circuits
22, 23, 65, 66, 30, and relay.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Circuits
30, 31, 65, 66, relay and relay circuit 30.
5. ECU grounds
6. ECU
Diagnostic Aid #8 “FUEL SYSTEM-ELECTRICAL”
(no fuel delivery)
Possible causes:
1. No fuel
2. Air in fuel rail
3. Fuel valve shut off
4. Fuel filter/line plugged
5. Injector circuit(s)
“24 Pin” (MSE 1.0) Plastic-Cased ECU: Circuits
16, 17, 45, and 45A.
“32 Pin” (MSE 1.1) Plastic-Cased ECU: Circuits
14,15, and 45.
6. Injector
7. ECU grounds
8. ECU
Diagnostic Aid #9 “FUEL SYSTEM” (fuel pressure)
Possible causes for low fuel system pressure:
1. Low fuel
2. Fuel filter plugged
3. Fuel supply line plugged
4. Pressure regulator
5. Fuel pump
Possible causes for high fuel system pressure:
1. Pressure regulator
2. Fuel return line plugged or restricted.
Diagnostic Aid #10 “BASIC ENGINE” (cranks but
will not run)
Possible causes:
1. Refer to basic engine troubleshooting charts
within service manual sections 3, 5, and 8.