3116 and 3126 Truck Engines Problem Engine Cranks But Will Not Start.

There are a number of possible reasons why a Cat 3126 engine might crank but not start. Some of the most common causes include:

  • Fuel problems: This could be anything from a lack of fuel to a problem with the fuel pump, injectors, or fuel filter.
  • Air problems: The engine may not be getting enough air, or the air intake may be clogged.
  • Compression problems: The engine may not be building enough compression to start. This could be due to a problem with the piston rings, valves, or head gasket.
  • Electrical problems: The engine may not be getting enough electricity to start. This could be due to a problem with the battery, starter, or alternator.

We can isolate the problem by observing the exhaust smoke.

If the Exhaust Smoke Cannot Be Seen While Starting the Probable Cause(s) are:

1. Fuel Supply Or Engine Oil Supply Low:

Check that there is a sufficient fuel supply to operate the engine and the engine oil level is at the desired level. Engine oil feeds the high pressure hydraulic pump.

2. No Power To ECM:

a. Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566, for Voltage Supply To The ECM Test.

b. Check for presence and correct installation and operation of aftermarket engine shutdown devices (not installed by Caterpillar). These devices usually interrupt power to the ECM.

c. Check the ECM power and ground circuits and connections. If battery voltage does not reach the ECM, wire a bypass circuit for power and ground as shown in “Battery Circuits Test” in the 3100 HEUI Electronic Troubleshooting Guide, SENR6566.

3. Software Problem:

a. Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566.

NOTE: A new ECM comes with an unprogrammed Personality Module in it. If the ECM has been replaced, the ECM WILL NOT COMMUNICATE and the ENGINE WILL NOT START until the integral Personality Module has had software flashed into it.

4. No Speed/Timing Signal:

a. While cranking the engine, observe engine rpm on a status screen of the EST. If the rpm reads 0 (zero) while cranking, there is a problem in the speed/timing circuit, or the engine cranking speed is below 100 rpm. At least 100 RPM is required to achieve reliable starting.
b. The cranking speed is typically 100 to 150 rpm with a cold engine. A cranking speed of 100 rpm or greater should create enough hydraulic oil pressure to operate the unit injectors. If cranking speed is below 100 rpm, refer to Problem 2: Engine Cranks But Turns Too Slowly. If cranking speed is above 100 rpm then use an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine, SENR6566, for Engine Speed/Timing Circuit Test.

5. Fuel System Problem:

a. Make sure that the engine is not out of fuel and verify that the fuel system is primed. Check engine fuel pressure while cranking. At 200 rpm pressure should read about 275 to 350 kPa (40 to 50 psi), measured at the inlet to the secondary fuel filter. At low idle, fuel pressure should be about 400 to 435 kPa (58 to 63 psi). If fuel pressure is zero then check to see that the cam/timing gear is turning the fuel pump. If fuel pressure is low then check fuel filters, fuel lines, etc. for restrictions. Check fuel transfer pump, valves and bypass. If the fuel system has been worked on, verify that the orificed check valve is mounted correctly on the fuel return line and is working, and that the correct orifice is installed.

b. Check for air in fuel by installing a 2P8278 sight glass on the return line. If access to the rear of the engine is restricted, install the sight glass on the return line at the tank. Check fuel transfer pump fittings and joints for air leaks. Check the unit injectors and sleeves for combustion gas leaks. Remove each unit injector and use a magnifying glass to inspect the base of the sleeve. The unit injector may also show evidence of leaking combustion gas.

NOTE: Refer to Disassembly And Assembly, SENR6553, for the proper procedure for unit injector removal and installation.

c. Check fuel quality. Refer to Truck Performance And Driveability Diagnostic Guide, LEBT3477.

d. In cold weather below 0°C (32°F), make sure that winter grade fuel is being used. Check for waxing in the fuel.

6. Incorrect Injection Actuation Pressure

a. Check dipstick to be sure oil level is normal.

NOTE: Refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting, SENR6566 for further diagnostics.

b. Check for air in the system. After opening or working on the high pressure hydraulic oil system, there may be air remaining in the system. To purge the air, crank the engine for thirty seconds at a time at least three times. Allow the starter to cool off for two minutes between each cranking period.

c. Check to see that oil is reaching the hydraulic pump inlet. Inspect the oil supply line from the engine oil gallery on the left side of the engine block to the pump inlet.

d. Check engine oil pressure with a gauge mounted to the oil gallery on the left side of the engine block. There should be about 28 to 55 kPa (4 to 8 psi) while cranking. If there is not any oil pressure then check for dilution of oil (dilution will lower oil pressure), engine oil pump, and pickup.

7. Slow Cranking:

Cranking speed should be a minimum of 100 rpm for engine starting. Refer to Problem 2: Engine Hard To Or Will Not Start.

If the Exhaust Smoke Can Be Seen While Starting, the Probable Cause(s) are:

8. Cold Outside Temperatures:

a. Using an electronic service tool check for logged or active diagnostic codes. Refer to 3100 HEUI Diesel Truck Engine, SENR6566, for Inlet Heater Driver Open Circuit or Inlet Heater Driver Short Circuit.

NOTE: It is normal to get white smoke while cranking and for a very brief period after starting the engine. For operation in cold and very cold temperatures, a winterfront cover or radiator shutters are recommended.

b. Check to see if the inlet air heater is inoperative. If the INLET AIR HEATER IS INOPERATIVE, then it is permissible to use starting aids such as ether. To repair the inlet air heater, refer to 3100 HEUI Diesel Truck Engine Electronic Troubleshooting SENR6566.

NOTICE

DO NOT USE ETHER IF THE INLET AIR HEATER IS WORKING, as there is possibility of fire or explosion when the ether contacts the heated surfaces.

c. Check fuel grade and quality. If cloud point is too high, waxing may result, plugging the fuel filters and lines. Refer to Truck Performance And Driveability Diagnostic guide.

9. Low Fuel Pressure:

Check fuel pressure with a gauge while cranking. Engine fuel pressure while cranking should read about 275 to 350 kPa (40 to 50 psi) at 200 rpm measured at the inlet to the secondary fuel filter.

10. Air In Fuel:

Check for air in fuel by installing a 2P8278 sight glass on the return line. If access to the rear of the engine is restricted, install the sight glass on the return line at the tank. Check fuel transfer pump fittings and joints for air leaks. Check the unit injectors and sleeves for combustion gas leaks. Remove each unit injector and use a magnifying glass to inspect the base of the sleeve. The unit injector may also show evidence of leaking combustion gas.

NOTE: Refer to Disassembly And Assembly, SENR6553, for the proper procedure for unit injector removal and installation.

11. Loss Of Compression:

Check valve clearances and make adjustments. Refer to the Testing And Adjusting section of this service manual. Low compression can also result from a blown head gasket, piston ring failure, incorrect installation, etc.

12. Water In Fuel:

Condensation may occur in fuel tanks, typically while standing overnight in cool or cold ambient temperatures. The use of a primary filter/water separator is recommended. If water is found in the fuel, it will be necessary to drain fuel tanks, lines and filters and refill with known good fuel of the correct grade, and replace fuel filters.

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