Top 10 7.3 Diesel Hard Start / No Start Diagnostic Procedures

A hard start or no start issue can be a troublesome problem to run into on the 7.3 Powerstroke. There are a number of sensors and other engine components that can cause both of these issues which makes it difficult to pinpoint what the exact problem might be.

This guide is going to discuss the 10 best things to check to fix a hard start or no start on a 7.3L Powerstroke diesel. Furthermore, we’ve included instructions on each step along the way to give you the info you need to check each component.

Top 10 7.3 Powerstroke Hard Start and No Start Diagnosis Steps

  1. Visual Engine / Chassis Inspection
  2. Check Engine Oil Level
  3. Intake / Exhaust Restriction
  4. Sufficient Clean Fuel
  5. Fuel Pump Pressure
  6. Perform KOEO On-Demand Self Test
  7. Retrieve / Clear Continuous DTCs
  8. KOEO Injector Electrical Self Test
  9. Check VPWR During Cranking
  10. Glow Plug System Operation

1) Visual Engine & Chassis Inspection

This is a visual inspection to check the general condition of the engine and look for obvious causes of a hard start or no start conditions.

Recommended Procedure:

  • Inspect fuel system, including the fuel tank and fuel lines for kinks, bends and/or leakage.
  • Check oil lines and high pressure pump (HPOP) in engine “V” for major oil leaks.
  • Inspect for coolant leaks at radiator and heater hoses and check coolant level.
  • Inspect wiring for correct routing and make sure no rubbing or chafing has occurred.
  • Inspect the in-line 42-way, injector driver module (IDM), powertrain control module (PCM) and sensor connectors to make sure they are completely seated and in good condition.

Possible Causes:

  • Loose or leaking fuel supply lines could cause the fuel system to lose prime.
  • Kinked or blocked fuel supply lines will create a fuel restriction.
  • Massive fuel or oil leaks could contribute to no start conditions.
  • Coolant leaks could indicate serious engine problems.
  • Electronic connectors may be damaged or not installed properly causing a no start condition. The camshaft position (CMP) sensor and the injection pressure regulator (IPR) are the two most critical electronic sensors/actuators to inspect in no start situations.

Tools Required:
Inspection light

2) Check 7.3 Powerstroke Engine Oil Levels

Check oil level with dipstick when vehicle is on level ground. If there is no oil or very little oil in the crankcase, the injectors will not operate.

If the oil level on the dipstick is overfull, it is possible the engine was incorrectly serviced or fuel is diluting the oil and filling the crankcase. Usually if a substantial amount of fuel is in the oil, it will have a fuel odor.

Inspect oil for color. A milky white oil indicates possible coolant contamination and will have an ethylene glycol odor.

Check service records for correct oil type and viscosity for the vehicle operating temperature. Single weight or 15W-40 oil is not recommended for cold ambient temperatures. Synthetic 5w-40 oil is recommended for cold ambient temperatures. Oil that has had extended drain intervals will have increased viscosity (become thicker) and will make engine cranking more difficult and starting less reliable at temperatures below freezing. Refer to the lube oil chart in the service manual or operator’s manual for the correct oil selection for temperature conditions.

The level in the oil reservoir should also be checked. Remove the inspection plug on top of the reservoir and check to see if the oil reservoir is full. (A reservoir that drains back after the engine has not been operated for a period of time can cause a hard start and die condition.) Filling the reservoir will allow the system to prime faster facilitating starting.

Possible Causes:

  • Oil level low — oil leak, oil consumption, incorrect servicing.
  • Oil level high — incorrect servicing, fuel dilution from fuel pump, fuel dilution from injector O-rings.
  • Oil contamination with coolant — oil cooler, head gasket, cylinder wall porosity, cavitation.
  • Low reservoir level — engine built dry (not pressure lubed), prolonged period of not running, leaking check valve in high pressure pump, excessive cranking without starting.

Tools Required:

1/4-inch drive ratchet or breaker bar to remove inspection plug on top of the High Pressure Oil Pump (HPOP).

3) Check for Intake or Exhaust Restriction

Checking for Intake Exhaust restriction is a a visual inspection to determine if an air intake or exhaust restriction is contributing to a no start or hard start condition.

If the engine does start with a high air intake or exhaust restriction, a considerable amount of black/blue smoke is produced.

Recommended Procedure:

Inspect the air cleaner inlet and ducting to assure that it is not blocked or collapsed. Inspect the air cleaner housing and filter for proper installation. Inspect the filter minder to assure intake restriction is below the red marks.

Inspect the exhaust back pressure device bellcrank during cranking and assure that it is not closing. Inspect the exhaust system for damaged or blocked pipes. When the tang is against the stop, the valve is fully open.

 Possible Causes

  • Snow, plastic bags or other foreign material may restrict airflow at the air inlet.
  • Misrouted air cleaner ducting.
  • On engines recently repaired, rags or cap plugs may have been inadvertently left in an air inlet pipe.
  • Exhaust back pressure device may be closing during cranking or stuck closed.
  • Tailpipe or muffler may have collapsed or been damaged or the catalytic converter is clogged.

4) Make Sure You Have Good Fuel

This is probably only relevant if you haven’t started or driven your 7.3L in awhile, but making sure it has good fuel in it is important for the combustion process to take place to get an engine started.

Check out our guide on the best diesel fuels to learn more.

5) Test Fuel Pump Pressure

To determine if there is sufficient fuel pressure for starting.

Recommended Procedure:

Connect Rotunda High Fuel Pressure Adapter 014-00931-3 or equivalent to the Schrader valve mounted in the fuel regulator block. Connect a line for a 160 psi gauge to the adapter. Crank engine at 100 rpm minimum and measure maximum fuel pressure.

Possible Causes:

  • A fuel filter could cause high restriction and low fuel pressure because of dirt or fuel jelling in cold ambient temperatures. Change filter and retest. (Note: It may take a couple of crank cycles to purge the air out of the fuel system.)
  • Debris in the fuel regulator valve will cause low fuel pressure. Disassemble, inspect and clean.
  • A kinked or severely bent fuel supply line or blockage at the pickup tube could cause restriction and therefore low fuel pressure.
  • A loose fuel line on the suction side of the fuel system could cause air to be ingested into the system and cause low fuel pressure.
  • The fuel pump could have internal damage, e.g., ruptured diaphragm, seized plunger or leaking check valves.

Tools Required:
0 to 160 psi fuel pressure gauge.
Rotunda High Fuel Pressure Adapter 014-00931-3 or equivalent line with 1/4-inch NPT fitting.

6) Perform a KOEO On-Demand Self Test

The purpose of this test is to ensure that the Powertrain Control Module (PCM) is working properly.

KOEO stands for Key On Engine Off. We have a full guide on how to perform this test here.

7) Read & Clear DTC’s / Engine Codes

Determine if the PCM has detected any historical or intermittent fault conditions that would cause a hard start/no start symptom. The condition that caused a continuous DTC may no longer exist.

Recommended Procedure:

  • Perform the necessary vehicle preparation and visual inspection.
  • Connect the OBDII Scan Tool / Tester to the DLC under the dash. Turn off accessories. If vehicle is equipped with an auxiliary powertrain control (rpm control), it must be turned off to perform self tests.
  • Turn key to on.
  • Record any codes displayed. (P1111 may be the only code displayed.)
  • Clear Continuous DTCs /  IDM trouble codes from memory.
  • After IDM trouble codes are cleared from memory. Repeat the KOEO On-Demand Self Test and KOEO Injector Electrical Self Test. Any IDM codes that reappear are IDM hard faults. If no IDM codes reappear, then the fault is an intermittent IDM fault.

Tools Required:
Rotunda New Generation Star (NGS) Tester 007-00500 or equivalent scan tool.

8) Do a KOEO Injector Electrical Test

Again, we have a complete guide on electric testing the injectors. The purpose here is to make sure the injector solenoids are working properly and the valves are opening to allow fuel to spray out of the injectors.

9) Check VPWR During Crank

To verify PCM power-up during cranking. Lack of power to PCM can cause a no start condition as well as fault code loss. Scan tools often require a minimum system voltage of 9.5 volts to avoid resetting.

Recommended Procedure:

Connect the OBDII Scan Tool to the data link connector (DLC) under the dash. Access VPWR PID on OBDII Scan tool and monitor while cranking the engine.

Possible Causes:

  • Low battery voltage.
  • Charging system problem.
  • Power circuit and ground faults to the PCM

Note: Battery voltage below 9.5 volts can cause the Sacn tool to reset. If the OBDII Scan Tool resets during a self test or while PID monitoring, it may be necessary to install a battery charger to maintain the correct voltage.

Tools Required:
Rotunda New Generation Star (NGS) Tester 007-00500 or equivalent Scan

10) Check the 7.3 Powerstroke Glow Plugs and Control Module / Relay

To determine if the glow plug system operation is sufficient to permit starting.

Recommended Procedure:

Check Relay Operation by installing a DVOM on the glow plug feed side of the glow plug relay (large stud with two wires connected). Turn the ignition key to the ON position but do not attempt to start. Note the time in seconds from when the key is turned on and the glow plug relay energizes until the glow plug relay de-energizes.

The glow plug relay makes a loud click noise which is easily heard when it energizes and de-energizes. The dome light will dim and the dash voltmeter will dip when the glow plugs are drawing current from the battery. Compare the times measured to the table (time will be affected by engine temperature, battery condition and vehicle altitude).

The voltage at the glow plug feed terminal may vary from 9 to 12 volts depending upon battery condition.

If battery voltage is not present, check for B+ at the power supply terminal (terminal with single large wire). Power for glow plug power supply is supplied from the starter relay through two fusible links at solenoid.

Check Glow Plug Operation

Disconnect all of the glow plug/injector harness connectors from the valve cover gaskets. With the Rotunda Glow Plug Injector Adapter 014-00935 or equivalent installed, measure glow plug resistance to ground. A resistance measurement of 0.1 to 2 ohms indicates a good glow plug.

Glow Plug Harness Continuity
Measure for continuity from the connector harness to the glow plug feed terminal on the glow plug relay. Resistance should be less than 0.1 to 1 ohm.

Incorrect measurements will result if all glow plug/injector connectors to valve cover are not disconnected.

Possible Causes:

Insufficient glow plug ON time will not allow enough heat to accumulate in the combustion chamber to easily facilitate starting. If the glow plug system ON time does not meet any of the specifications in the accompanying chart the problem is most likely a faulty wire harness connection, ground connections or glow plug relay.

If the glow plug resistance to ground is high, the most likely causes are an open under valve cover (UVC) harness or an open glow plug.

Tools Required:

  • Rotunda Digital Volt-Ohm Multimeter (DVOM) 105-00050 or equivalent
  • Rotunda Glow Plug Injection Adapter 014-00935 or equivalent
  • Stop watch or equivalent

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One Comment

  1. I have a 1988 Ford F350 7.3 l. Non-turbo. Can be extremely hard to start two brand new batteries. If I give it just a little shot of ether. It’ll fire right up. Even after I lent the glow plugs cycle as I crank it over it gets to the point where it will barely turn but as a starter takes over it’ll fire up. Also, in the visor it says to hold it to the floor and cold temperatures while starting. Is this recommended? What could be the problem? It used to crank over fine

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