Ford F150 Pickup. Instruction - part 1395

8) Check Fuel Pump Intercept Harness 
Turn ignition off. Ensure in-line harness connector C4002 is disconnected. Connect a test light between 
chassis ground and in-line harness connector C4002F terminal "D" (White wire). 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, repair or replace circuit between inertia 
switch and connector C4002 as necessary. Start engine in ALT fuel mode to ensure concern is no longer 
present. 

9) Check Compuvalve Main Harness 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect 
compuvalve harness connector C1294 and in-line 8-pin harness connector C406. Ensure compuvalve in-
line harness connector C4002 is disconnected. Measure resistance of White wire between compuvalve 
harness connector C1294 terminal No. 3 and in-line harness connector C4002F terminal "F". See Fig. 7 , 
Fig. 23 and Fig. 28 . If all resistance measurements are less than 5 ohms, go to next step. If any resistance 
measurement is 5 ohms or more, repair or replace compuvalve main harness as necessary. Reconnect all 
connectors, connecting bi-fuel relay module power supply connector C495 last. Start engine in ALT fuel 
mode to ensure concern is no longer present. 

10) 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. Proceed as follows: 

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 
LOCKOFF SOLENOID under FUEL SYSTEMS in REMOVAL & INSTALLATION - F150 PICKUP 
- BI-FUEL - GASOLINE/LPG article. 

TEST AD: NO START - ALT FUEL SWITCH INDICATOR IS ON STEADY 

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:  

NOTE:

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

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 .

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

  

z

Manifold Absolute Pressure (MAP) sensor.  

z

MAP tap assembly.  

z

Compuvalve.  

z

Harness circuits.  

Testing 

1) Monitor MAP & RPM PIDs 
Turn ignition off. Connect scan tool to Data Link Connector (DLC). Place ALT fuel switch in GAS 
position. Turn ignition on. With ignition on and engine off, MAP PID should read about 14 psi and RPM 
PID should read zero. Using scan tool, access AFCM and select MAP and RPM PIDs from PID/DATA 
MONITOR & RECORD menu. Start engine and allow to idle. If MAP PID value drops with engine 
running and RPM PID value reads actual engine speed, go to step 5) . If MAP PID drops with engine 
running and RPM PID does not read actual engine speed, go to next step. If MAP PID does not drop with 
engine running and RPM PID reads actual engine speed, go to step 4) . 

2) Check Tach Circuits For Opens 
 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect in-
line 42-pin connector C133. Disconnect in-line 10-pin connector C421. Using DVOM, measure 
resistance of Dark Blue wire between in-line harness connector C133M terminal No. 28 and in-line 
harness connector C421F terminal "H", and chassis ground. Also, measure resistance of Gray wire 
between in-line harness connector C133M terminal No. 22 and in-line harness connector C421F terminal 
"J", and chassis ground. See Fig. 15 and Fig. 19 . If resistances are less than 5 ohms between harness 
connectors C133 and C421 and more than 10 k/ohms between harness connector C421 and chassis 
ground, go to next step. If any resistance is 5 ohms or more between harness connectors C133 and C421 
or 10 k/ohms or less between harness connector C421 and chassis ground, repair open or short to ground 
in affected circuit. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in 
ELECTRICAL. 

3) Check Compuvalve Harness 

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 .

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 .

 

2003 Ford Pickup F150 

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

  

Disconnect bi-fuel relay module power supply harness connector C495. Disconnect compuvalve harness 
connector C1294. Ensure in-line harness connector C421 is disconnected. Using DVOM, measure 
resistance of White wire between compuvalve harness connector C1294 terminal No. 34 and in-line 
harness connector C421M terminal "H". Also measure resistance of White wire between compuvalve 
harness connector C1294 terminal No. 38 and in-line harness connector C421M terminal "J". See Fig. 7 
and Fig. 19 . If resistances are less than 5 ohms, perform COMPUVALVE CHECK under QUICK 
TEST. If no-start fault still exists, replace compuvalve. If either resistance measurement is 5 ohms or 
more, repair open in affected circuit. See ENGINE PERFORMANCE in SYSTEM WIRING 
DIAGRAMS article in ELECTRICAL. 

4) Check MAP Sensor Operation 
Disconnect MAP line from compuvalve. Connect hand-held vacuum pump to MAP inlet on compuvalve. 
Place ALT fuel switch in GAS position. Turn ignition on. Using scan tool, access AFCM MAP PID from 
PID/DATA MONITOR & RECORD menu. Start engine and allow to idle. Record MAP PID value. 
Apply vacuum to MAP sensor inlet on compuvalve. Record MAP PID value. If MAP PID value reads 
about 14 psi before applying vacuum and value changes after applying vacuum to compuvalve, check for 
blockage or leaks in MAP line assembly. Repair or replace MAP line assembly as necessary. If MAP PID 
value reads about 14 psi before applying vacuum and value does not change after applying vacuum to 
compuvalve, perform COMPUVALVE CHECK under QUICK TEST. If no-start fault still exists, 
replace compuvalve. 

5) Check Compuvalve Outlet Line For Blockage 
 
Turn ignition off. Release ALT fuel system pressure. See FUEL SYSTEM PRESSURE RELEASE 
under FUEL SYSTEMS in REMOVAL & INSTALLATION - F150 PICKUP - BI-FUEL - 
GASOLINE/LPG article. Disconnect compuvalve outlet line. Apply a regulated amount of air pressure to 
compuvalve outlet line. Have an assistant listen for air escaping from exhaust tailpipe. If air is heard 
escaping from exhaust tailpipe, go to next step. If no air is heard escaping from exhaust tailpipe, replace 
compuvalve outlet line/tuning "T". See FUEL RAILS & INJECTORS under FUEL SYSTEMS in 
REMOVAL & INSTALLATION - F150 PICKUP - BI-FUEL - GASOLINE/LPG article. 

6) Check Injector Power Supply 
 
Turn ignition off. Disconnect high flow injector assembly connector C1297 and low flow injector 
assembly connector C1289. Turn ignition on. Using DVOM, measure voltage between chassis ground 
and harness connector C1297M terminals "G" and "H". Also, measure voltage between chassis ground 
and harness connector C1289M terminal "D". See Fig. 23 and Fig. 26 . If both voltages are more than 10 
volts, go to step 8) . If either voltage is 10 volts or less, go to next step. 

NOTE:

Restrictor in MAP line is a calibrated length. DO NOT change length of 
restrictor if repairs to MAP line are necessary.

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 .

 

2003 Ford Pickup F150 

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

  

7) Check Injector Power Circuits From Bi-Fuel Relay Module 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect bi-
fuel relay module harness connector C410. Disconnect compuvalve harness connector C1294. Reconnect 
bi-fuel relay module power supply harness connector C495. Connect a 5-amp fused jumper wire between 
chassis ground and bi-fuel relay module harness connector C410F terminal "A". Turn ignition on. Using 
DVOM, measure voltage between chassis ground and bi-fuel relay module harness connector C410F 
terminal "F", "G" and "H". See Fig. 15 . If voltage is more than 10 volts, repair or replace compuvalve 
main harness. See ENGINE PERFORMANCE in SYSTEM WIRING DIAGRAMS article in 
ELECTRICAL. If voltage is 10 volts or less, replace bi-fuel relay module. 

8) Check Injector Circuits 
 
Turn ignition off. Disconnect bi-fuel relay module power supply harness connector C495. Disconnect 
compuvalve connector C1294. Ensure in-line harness connector C1297 is disconnected. Inspect injector 
circuits for physical damage. If damaged, repair as necessary. If no damage exists, go to next step. 

9) Check Main Harness Injector Circuits For Open 
 
Turn ignition off. Ensure compuvalve harness connector C1294, low flow injector assembly connector 
C1289 and high flow injector assembly connector C1297 are disconnected. Using DVOM, measure 
resistance between specified connector terminals. See MAIN HARNESS INJECTOR CIRCUIT 
CHECK table. See Fig. 7 , Fig. 23 and Fig. 26 . Also measure resistance between harness connector 
terminals and ground. If all resistances are less than 5 ohms between specified injector assembly 
connector and compuvalve harness connector, and more than 10 k/ohms between specified injector 
assembly connector and ground, go to next step. If any resistance is 5 ohms or more between specified 
injector assembly connector and compuvalve harness connector, or 10 k/ohms or less between specified 
injector assembly and ground, repair open or short to ground in affected circuit. See ENGINE 
PERFORMANCE in SYSTEM WIRING DIAGRAMS article in ELECTRICAL. 

MAIN HARNESS INJECTOR CIRCUIT CHECK 

NOTE:

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

Measure Between Injector Assembly Harness 
Connector No. & Terminal No.

Compuvalve Harness Connector No.

C1294F Terminal No.

C1289F 

(1)

"A"

17

"B"

19

C1297F 

(2)

"A"

45

"B"

47

"C"

49

"D"

51

"E"

53
55

 

2003 Ford Pickup F150 

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