Diagnostic Aids

Insufficient glow plug "On" time will not allow enough heat to accumulate in combustion chamber resulting in a hard start condition. If glow plug system "On" time is insufficient, probable cause is a faulty wiring harness connector, bad ground connection or defective glow plug relay. If glow plug resistance to ground is high, probable cause is an open circuit in Under Valve Cover (UVC) wiring harness or an open glow plug.

1. Connect a DVOM between ground and Black/Orange wire at glow plug relay. See Fig 1 . Turn ignition on. If battery voltage is present, go to next step. If battery voltage is not present, locate and repair open circuit in Black/Orange wire between glow plug relay and starter relay.
2. Turn ignition off. Connect DVOM between ground and Brown wire at glow plug relay. Turn ignition on and note how long is takes for glow plug relay to energize and de-energize ("On" time). Relay will make a loud click noise when it energizes. If relay "On" time is not as specified, replace relay. See GLOW PLUG RELAY SPECIFICATIONS table. If "On" time is as specified, go to next step.
   GLOW PLUG RELAY SPECIFICATIONS ⁽¹⁾
   
   

   Engine Oil Temperature °F (°C)		"On" Time Seconds
   Federal vehicles
   32 (0)		120
   50 (10)		60
   68 (20)		30
   86 (30)		0
   Calif. vehicles
   14 (-10)		120
   68 (20)		70
   122 (50)		40
   131 (55)		60
   (1) Specification listed is with vehicle at sea level and battery voltage at 12 volts. Specification is approximate.

   Fig 1: Checking Power To Glow Plug Relay

   Courtesy of FORD MOTOR CO.
   NOTE: Each valve cover gasket has 2 fuel injector connectors that are part of the gasket. Each connector is responsible for 2 fuel injectors. If connector is faulty, replace valve cover gasket.
3. Turn ignition off. Disconnect all 4 injector connectors at valve cover gaskets. Install Glow Plug Injector Adapter (014-00935) to any injector connector at valve cover gasket. See Fig 2 .
   NOTE: If all injector connectors are not disconnected at both valve cover gaskets, resistance measurements will be incorrect.
4. Measure resistance between ground and each glow plug test point at glow plug injector adapter. If all readings are .1-2.0 ohms, go to next step. If any reading is not .1-2.0 ohms, probable cause is an open in Under Valve Cover (UVC) wiring harness or an open glow plug. Repair as necessary.
5. Measure resistance between Brown wire at glow plug relay and each glow plug test point at glow plug injector adapter. If all readings are .1-1.0 ohm, no problem is indicated at this time. If any reading is not .1-1.0 ohm, locate and repair open circuit.

Fig 2: Checking Glow Plug Resistance

Courtesy of FORD MOTOR CO.