1994 PCED OBDI-A | SECTION 18A: Diesel Diagnosis — 7.3L DI Engine |
Use the following chart to diagnose hard start/no start concerns. More complete procedures appear on the following pages.
The purpose of this test is to see if the fuel system is getting sufficient clean fuel to start and run.
Route a hose from the fuel drain line to a clear container and open the drain. Crank the engine and observe the fuel flowing into the container. Stop cranking the engine when the container is half full.
Inspect the WATER IN FUEL light while cranking the engine. If the light is illuminated, the fuel is probably contaminated with water.
Flow out of the drain should be a steady stream. Insufficient flow could indicate fuel supply or fuel system problems.
Inspect fuel in the container. It should be straw colored, but not cloudy. It also should be free of water and contaminants. Dyed red or blue fuel indicates off-highway fuel.
If engine oil is present in the fuel it may indicate an injector O-ring leak and subsequent loss of rail pressure. If that is suspected, check rail pressure during engine cranking (Test 11a). Some sediment and water may be present in the fuel sample if the fuel filter has not been serviced for a prolonged period of time and or if the sediment and water have not been drained recently. If that is the case a second sample may be required to determine fuel quality.
No fuel in tank. If equipped with a fuel line valve, it could be shut off. If equipped with dual tanks, the switch valve could be faulty, fuel feed line could be broken or crimped, the fuel could be jelled (most likely in cold weather with No. 2 fuel) or the pickup tube screen in tank could be clogged.
Cloudy fuel indicates that the fuel may not be a suitable grade for cold temperatures, excessive water or contaminants may indicate that the tank and fuel system may need to be flushed and cleaned.
Clear container — approximately 1 quart
This is a visual inspection to check the general condition of the engine and look for obvious causes of hard start or no start conditions.
Inspect fuel system including tank and lines for kinks, bends and/or leakage. Check oil lines and high-pressure pump 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, IDM, PCM and sensor connectors to make sure they are completely seated and in good condition.
Loose or leaking fuel supply lines could cause fuel system to lose prime. Kinked or blocked fuel supply lines will create 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 CMP sensor and the IPR valve are the two most critical electronic sensors/actuators to inspect in no start situations.)
Inspection light
To determine if there is enough oil or oil of sufficient quality to operate the injectors.
Check oil level with oil level gauge 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 gauge 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 15 W 40 oil is not 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 in top of 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.
Oil level low — oil leak, oil consumption, incorrect servicing.
Oil level high — incorrect servicing, fuel dilution from lift pump, fuel dilution from injector O-rings.
Oil contamination with coolant — oil cooler, head gasket, porosity
Low reservoir level — engine built dry (not pressure lubed), prolonged period of not running, leaking check valve in high-pressure pump.
1/4-inch drive ratchet or breaker bar to remove inspection plug.
This is a visual inspection to determine if intake or exhaust restriction is contributing to a no start or hard start condition. If the engine does start with high inlet or exhaust restriction, a considerable amount of black/blue smoke is produced.
Inspect the air cleaner inlet and ducting to assure that it is not blocked or collapsed. Inspect 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.
Snow, plastic bags or other foreign material may block the air cleaner inlet. Misrouted air cleaner ducting may collapse when the hood is shut. On engines recently repaired, rags or cap plugs may have been inadvertently left in an intake pipe.
The exhaust back pressure device may be closing during cranking or stuck closed.
The tailpipe or muffler may have collapsed or been damaged.
None
To determine if the PCM has detected any fault conditions that would cause a hard start or no start condition.
With all accessories off and the ignition key off, connect the Super STAR II tester to the correct connector under the hood. Latch the center button on the tester ON and turn the ignition key to the RUN position.
Record all codes transmitted. (Code 10 is the separator code between current and historical faults.)
If any fault codes other than the PASS code sequence of 111 10 111 911 is transmitted or if no codes are transmitted, refer to Diagnostic Trouble Code Description Chart in Scan Tool Diagnostic Tests.
All current faults must be fixed before proceeding.
The most likely PCM detectable faults that will cause a no start or hard start condition are CMP sensor inactive faults, IPR output circuit check fault, FDCS and CID output circuit check faults.
Rotunda Super STAR II tester 007-0041B
To determine if there is sufficient voltage and current to enable the injectors, IDM and PCM.
Install a DVOM (digital volt ohmmeter) on the battery terminals. With all accessories off and after the glow plug lamp has gone off, crank the engine and observe the lowest voltage obtained during cranking. If the minimum voltage is below 7 volts it is possible the power relays for the IDM and PCM are resetting or there may not be enough current available for the IDM to operate the injectors.
Discharged battery, poor battery connections, damaged battery, charging system problems.
Rotunda DVOM 105-00050
To verify PCM power-up. Lack of power to the PCM can cause a no start condition as well as fault code loss.
Install the breakout box; leave the PCM connected.
Measure voltage at PCM Pins 71 and 97 to 91 while cranking the engine. The expected value is battery voltage. If battery voltage is not present or if it drops out as the engine is cranking, it can be assumed that the PCM is not powered up. Verify the condition with the breakout box installed.
Poor connections from battery to relays, bad or reversed diode for PCM power, shorted power feed wire from battery.
Rotunda DVOM 105-00050
To determine if there is sufficient fuel pressure for starting.
Connect line for 160 psi gauge to the Schrader valve mounted in the fuel regulator block. Crank engine at 100 rpm minimum and measure maximum fuel pressure.
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.
0 to 160 psi fuel pressure gauge, appropriate line with 1/4-inch NPT fitting (or Schrader valve connector if equipped)
To determine if the glow plug system operation is sufficient to permit starting.
Relay Operation
Install 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 not present check for B+ at power supply terminal (terminal with single large wire). Power for glow plug power supply is supplied from starter relay through two fusible links at solenoid.
Glow Plug Operation
Disconnect the glow plug/injector harness connectors from the valve cover gasket. With the pigtail installed, measure glow plug resistance to ground (preferably B-). A resistance measurement of 1 to 5 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.
Incorrect measurements will result if all glow plug/injector connectors to valve cover are not disconnected.
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 UVC (under valve cover) harness or open glow plug.
Rotunda DVOM 105-00050, pigtail connector, stop watch or equivalent
To determine if the CMP (camshaft position) sensor circuit is functioning.
With all accessories and the ignition key off, install the Super STAR II tester. Latch the STI button in the center of the STAR tester and crank the engine. Then if the CMP sensor is functioning, the MIL (malfunction indicator lamp) will flash in relation with engine speed. If the lamp is not flashing as the engine is cranking, the PCM may not be receiving a CMP sensor signal.
If a Super STAR II tester is not available, ground the STI wire at the STAR test connector and perform test.
It is only necessary to perform this test if 10a failed. Turn the ignition key and all accessories off. Disconnect the CMP sensor connector and inspect the sensor and harness pins for corrosion, pitting, bent pins or any condition that will cause a bad connection.
(CMP Ground)
With the key and all accessories off, measure the resistance of point A in the harness connector to ground (B-). This is the CMP ground circuit and is grounded through filter circuit in the PCM. If any accessories are pulling an electrical load from the batteries, this resistance reading will fluctuate and not be stable. The purpose of this measurement is to determine if the CMP ground circuit is open.
(CMP Vref)
After determining that the CMP ground is good, turn the ignition key to the RUN position and measure the voltage from battery ground (B-) to point B. Point B at the CMP harness connection is the power supply for the CMP sensor. A 5-volt signal indicates a complete circuit from the PCM to the CMP sensor.
Measure from point C to battery ground with the ignition key on. Point C is a high signal supplied by the PCM to the CMP sensor. The PCM determines engine position when the CMP sensor pulls the high signal from the PCM down to approximately 2 volts as the windows in the target wheel pass by the sensor. With the CMP connector disconnected, point C should measure approximately 12 volts.
The problem is most likely a faulty wire harness connection, poor CMP ground connection, incorrect CMP sensor to target wheel spacing or defective sensor.
Rotunda DVOM 105-00050, Super Rotunda STAR II tester 007-0041B or ground wire
To determine if the injection control system can supply enough injection control pressure to sustain starting.
A KOEO test should have been performed prior to this test to ensure the ICP sensor signal is valid. A current or historical fault indicating an out of range high or low ICP signal indicates an ICP sensor or circuit fault and will affect engine starting and running.
Install the breakout box to the 104 pin connector with the PCM installed. Connect the negative lead of the DVOM to signal ground (Pin 91) and the positive lead to the ICP signal (Pin 87). Crank the engine and monitor the ICP signal. Compare the value monitored to the values in the table below.
If the signal does not meet the minimum specification, the injectors are not being enabled by the PCM because of insufficient pressure.
An inactive CMP signal will command an ICP value of .4 to .5 volt or ( ) psi. If this condition is existing, historical fault code 818 should be present. An open or shorted IPR (injection pressure regulator) will also indicate a .4 to .5 volt reading. Fault code 546 should be set during a KOEO test if this has occurred.
Removing the plug on top of the oil reservoir and checking the level of oil will determine if oil is being supplied to the high-pressure pump.
Removing the ICP sensor and inspecting the level in the oil rail will determine if oil is being supplied to the rail. If the oil is up to the sensor level at both locations, continue to test 11b to determine the cause of low injection control pressure.
Isolate the cause of low injection control pressure.
Note: Only perform the injector control pressure test if the system has failed Injector Control Pressure Test 11a.
(Right Cylinder Head Check)
Remove the high-pressure hose from the right cylinder head. Use a fuel/oil/turbo protector cap set, Tool Number T94T-9395-AH and install into the high-pressure hose to block it off. Connect ICP sensor cable T94-50-A to the ICP sensor. Connect a DVOM and crank the engine and monitor the signal, the DVOM should read 1 to 4 volts. Caution: The engine may start! If the engine starts or if the ICP pressure is now within specifications, the injection control pressure leak has been isolated to the right cylinder head. Inspect the fuel to see if oil is in the fuel. If no oil is present in the fuel, remove the valve cover, crank the engine and inspect the injector body and injector bore area for leakage. Caution: Oil is under high pressure!
(Left Cylinder Head Check)
Install right side high-pressure hose to the cylinder head. Remove the left side high-pressure hose and install ICP adapter plug into hose. Remove the ICP sensor and install in the end of the adapter plug. Connect ICP sensor cable T94-50-A to the ICP sensor. Connect a DVOM as shown in the following illustration. Crank the engine and monitor the signal, the DVOM should read 1 to 4 volts.
(IPR and High Pressure Pump)
If injection control pressure is still low after isolating both cylinder heads, use the plain flare plug to block the right high-pressure hose and crank the engine. This has effectively deadheaded the high pressure pump. To test the system connect the ICP sensor cable T94-50-A to the ICP sensor. Then connect a DVOM as shown in the following illustration. Crank engine and monitor the signal, the DVOM should show 1 to 4 volts. If pressure has still not developed, inspect the IPR (injection pressure regulator valve) for debris and/or replace with a known good valve and retest. If a low pressure condition still exists, the problem is most likely with the high-pressure pump or the high-pressure pump drive gear.
Rotunda DVOM 105-00050, ICP jumper harness/probe (or Rotunda 104 pin breakout box 014-00950), blocking plugs