Ford F150 Pickup. Manual — part 1394

Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect
compuvalve harness connector C1294. Ensure bi-fuel relay module connector C410 is disconnected.
Using DVOM, measure resistance between chassis ground and bi-fuel relay module harness connector
C410M terminal "A". Also, measure resistance between specified compuvalve harness connector
terminals and bi-fuel relay module harness connector terminals. See COMPUVALVE MAIN
HARNESS CONTINUITY TEST table. See Fig. 7 and Fig. 15 . If all resistances are less than 5 ohms,
perform COMPUVALVE CHECK under QUICK TEST. If no-start fault still exists, replace
compuvalve. If any resistance is 5 ohms or more, repair open in affected circuit. See ENGINE
PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL.

COMPUVALVE MAIN HARNESS CONTINUITY TEST

8) Check ALT Fuel Switch Circuit Voltage

Turn ignition off. Disconnect compuvalve 10-pin in-line harness connector C422, located in rear right
side of engine compartment. Turn ignition on. Using DVOM, measure voltage between chassis ground
and in-line harness connector C422M terminal "E". See Fig. 15 . If voltage is 10 volts or less, go to next
step. If voltage is more than 10 volts, go to step 10) .

9) Check Power To ALT Fuel Switch
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect bi-
fuel relay harness connector C410. Reconnect bi-fuel relay module power supply harness connector
C495. Turn ignition on.

Connect a 5-amp fused jumper wire between chassis ground and bi-fuel relay module harness connector
C410F terminal "A". Using DVOM, measure voltage between chassis ground and bi-fuel relay module
harness connector C410F terminals "D" and "E" (White wires). See Fig. 15 . If both voltages are more
than 10 volts, replace compuvalve main harness. If either voltage is 10 volts or less, replace bi-fuel relay
module.

10) Check Circuits To ALT Fuel Switch

Bi-Fuel Relay Harness Connector C410M
Terminal

Compuvalve Harness Connector C1294 Terminal

No.

"C"

2

"B"

5

"D"

9, 11 & 13

"E"

9, 11 & 13

CAUTION: Always disconnect bi-fuel relay module power supply 3-pin harness

connector C495 before disconnecting or reconnecting compuvalve
main harness connector C1294 to avoid damaging compuvalve or
connectors. See Fig. 6 .

NOTE:

Bi-fuel power relay should "click" when connector C410F terminal "A" is
grounded.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/LPG

Ensure compuvalve 10-pin in-line harness connector C422 is disconnected. Place ALT fuel switch in
ALT position. Using DVOM, measure resistance between in-line harness connector C422F terminal
"F" (Yellow wire) and terminal "H" (Dark Green wire). See Fig. 15 . If resistance is 5 ohms or more with
switch in ALT position, go to next step. If resistance is less than 5 ohms with switch in ALT position, go
to step 12) .

11) Check ALT Fuel Switch Operation

Disconnect ALT fuel switch 3-pin connector C4013. Place ALT fuel switch in ALT position. Using
DVOM, measure resistance between ALT fuel switch connector C4013M terminal "B" (Yellow wire) and
terminal "C" (Dark Green wire). See Fig. 3 . If resistance is less than 5 ohms, repair open in affected
circuit between ALT fuel switch connector C4013 and compuvalve in-line harness connector C422. If
resistance is 5 ohms or more, check for open in Yellow or Dark Green wires between ALT fuel switch
connector C4013 and ALT fuel switch. See ENGINE PERFORMANCE in SYSTEM WIRING
DIAGRAMS article in ELECTRICAL. Repair as necessary. If circuits are okay, replace ALT fuel switch.

12) Check Circuit Between ALT Fuel Switch & Compuvalve
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect
compuvalve harness connector C1294. Using DVOM, measure resistance of White wire between
compuvalve harness connector C422M terminal "F" and compuvalve harness connector C1294 terminal
No. 46. See Fig. 7 and Fig. 15 . If resistance is less than 5 ohms, perform COMPUVALVE CHECK
under QUICK TEST. If no-start fault still exists, replace compuvalve. If resistance is 5 ohms or more,
repair open in White wire between compuvalve harness connector C422 and compuvalve harness
connector C1294. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in
ELECTRICAL.

TEST AC: NO START - ALT FUEL SWITCH INDICATOR IS ON, THEN OFF

Diagnostic Aids

Enter this test only when all steps under QUICK TEST have been successfully completed and engine still does
not start or if directed here from another test or chart. This test is only intended to diagnose:

z

Solenoid tank valve/lockoff solenoid.

z

Alternate fuel lines and filters.

z

Compuvalve.

CAUTION: Be very careful when probing compuvalve harness connector

terminals. These terminals can be damaged if overstressed, resulting
in harness replacement.

NOTE:

This fault can be mistaken as an auto switch to GAS mode condition. Verify
LPG fuel level using fuel gauge mounted to LPG tank before continuing
diagnostics. Ensure manual shutoff valves (1/4 turn valves) and manual tank
valves (if equipped) are open.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/LPG

Testing

1) Check For DTCS
Turn ignition off. Connect scan tool to Data Link Connector (DLC). Turn ignition on. Using scan tool,
access PCM and retrieve any stored DTCs. Using scan tool, access AFCM and record any stored DTCs. If
any PCM DTCs are present, go to DIAGNOSTIC TROUBLE CODE DEFINITIONS in SELF-
DIAGNOSTICS - CNG, FLEX-FUEL & GASOLINE article. If any AFCM DTCs are present, go to
DIAGNOSTIC TROUBLE CODE DEFINITIONS and repair as necessary. If no DTCs are present, go
to next step.

2) Verify No-Start Concern
Place ALT fuel switch is in ALT position. Attempt to start engine. If engine starts with ALT fuel switch
in ALT position, ALT fuel system is operating properly at this time. If concern is intermittent, see
INTERMITTENTS in TROUBLE SHOOTING - NO CODES - BI-FUEL - GASOLINE/LPG article. If
engine does not start with ALT fuel switch in ALT position, go to next step.

3) Access AFCM FRPREAB PID
Connect scan tool to DLC. Using scan tool, access AFCM and select FRPREAB PID from PID/DATA
MONITOR & RECORD menu. Turn ignition off, then on. Select FRPREAB PID from PID/DATA
MONITOR & RECORD menu and record value. Monitor FRPREAB PID. If FRPREAB PID value is
less than 26 psi, go to next step. If FRPREAB PID value is 26 psi or more (LPG), go to step 10) .

4) Monitor FRPREAB PID Leakdown
Ensure scan tool is connected to DLC. Using scan tool, access AFCM and monitor FRPREAB PID from

NOTE:

During bi-fuel diagnostics, intermittent failures are possible. Perform wiggle
test and tap lightly on relays during testing. Ensure vehicle has LPG before
continuing with diagnostics.

CAUTION: Always disconnect bi-fuel relay module power supply 3-pin harness

connector C495 before disconnecting or reconnecting compuvalve
main harness connector C1294 to avoid damaging compuvalve or
connectors. See Fig. 6 .

NOTE:

Ensure EEC system calibration is for current Bi-Fuel code. On LPG
equipped vehicles, Engine Coolant Temperature (ECT) must above 20°F (-
7°C) or ALT fuel system may default to GAS mode.

NOTE:

Minimum FRPREAB PID values required to illuminate ALT fuel selector
switch indicator is 26 psi.

NOTE:

Before beginning leakdown test, check all fuel connections at vaporizer,
regulator, and compuvalve for leaks. See LEAK TEST - ALL BI-FUEL
VEHICLES under FUEL SYSTEMS in SYSTEM & COMPONENT TESTING -
BI-FUEL - GASOLINE/LPG article.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/LPG

PID/DATA MONITOR & RECORD menu. Turn ignition off, then on. Record FRPREAB PID value at
ignition on. Wait 2 minutes. If FRPREAB PID value drops 10 psi or more, go to step 10) . If FRPREAB
PID drops less than 10 psi, go to next step.

5) Check Fuel Level, Tank Valve & Fuel Filter
On LPG models, close tank valve and then fully open tank valve (open slowly to ensure excess flow
valve does not close). Tank valve is located on LPG fuel tank. For additional information, see
LIQUEFIED PETROLEUM GAS FUEL TANK EVACUATING under FUEL SYSTEM PRESSURE
RELEASE under FUEL SYSTEMS in REMOVAL & INSTALLATION - F150 PICKUP - BI-FUEL -
GASOLINE/LPG article. Turn ignition on. Using scan tool, access AFCM and select FTP PID from
PID/DATA MONITOR & RECORD menu. Monitor FTP PID. Proceed as follows:

z

If FTP PID value is less than 26 psi, go to next step.

z

If FTP PID value is 26 psi or more, start engine in ALT fuel mode to ensure concern is no longer
present.

6) Check Vaporizer Lockoff Solenoid Signal
Turn ignition off. Disconnect in-line harness connector C4002. Connect a test light between in-line
harness connector C4002F terminal "D" and "F" (both White wires). See Fig. 28 . Observe test light and
turn ignition on. If test light illuminates momentarily when ignition is turned on, go to next step. If test
light does not illuminate when ignition is turned on, go to step 8) .

7) Check Lockoff Solenoid Coil Resistance
Turn ignition off. Ensure in-line harness connector C4002 is disconnected. Gently wiggle connection and
flex wires around diode splice. Diode is located in harness near connector. Resistance value must remain
within one ohm while wires are being flexed and connection wiggled.

Using DVOM, measure resistance between in-line harness connector C4002M terminal "D" (White wire)
and terminal "F" (Yellow wire). See Fig. 28 . If resistance is 8-18 ohms, replace mechanically stuck
lockoff solenoid. If resistance is not 8-18 ohms, replace lockoff solenoid for internal open circuit. See
under FUEL SYSTEMS LOCKOFF SOLENOID in REMOVAL & INSTALLATION - F150 PICKUP
- BI-FUEL - GASOLINE/LPG article.

NOTE:

Before beginning the leakdown test, check all fuel connections at the
vaporizer, regulator, and compuvalve for leaks.

CAUTION: When connecting test light, DO NOT short across terminals as

damage to compuvalve may occur.

NOTE:

This circuit is powered from inertia switch. Test light will only illuminate
momentarily.

CAUTION: DO NOT bend diode or flex wires more than 30 degrees.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Self-Diagnostics - Bi-Fuel - Gasoline/LPG