This article mainly introduces how to solve the problem of Caterpillar 325C excavator engine not 

igniting, not running smoothly or unstable. 

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  NOTE: If the fault is intermittent and does not repeat, see the "Intermittent Low Power or Power 

Cutout" section. If the fault is persistent and does not If repeated, continue this procedure. 

 (1) Possible reasons. 

 1) Diagnostic code. 

 2) Electrical connector.  

3) Cold mode.  

4)Throttle signal. 

 5)Injection driving pressure.

  6) Single fuel injector. 

 7) Fuel supply. 

 8) Intake and exhaust systems.

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(2) Recommended measures.  

NOTE: If the failure occurs only under certain operating conditions (high idle speed, full load, engine 

operating temperature, etc.), test the engine under these conditions. Failure to diagnose and eliminate 

fault symptoms under these conditions can be misleading.  

1) Diagnostic code. Check the Caterpillar Electronic Technology (Cat ET) for self-diagnostic codes.

  Before continuing with this procedure, first All self-diagnostic codes perform troubleshooting and 

troubleshooting. 

 2) Electrical connector. Check that ECM connectors J1/P1 and J2/P2 and unit injector connector are 

installed correctly. 

 3) Cold mode. Use Cat ET to verify that the engine is out of cold mode. Operating in cold mode can 

cause the engine to run erratically and cause Machine power is limited. 

 4)Throttle signal. Monitor the throttle signal on Cat ET. Check whether the throttle signal is stable 

from the low idle position to the high idle position. Certainly . 

 5)Injection driving pressure. ① Check the engine oil level. Engine oil supplies the injection drive 

pressure circuit. Engine oil must be at the correct level for fuel to spray shoot. NOTE: If oil has been 

drained from the unit injector hydraulic pump, the pump must be primed. 

 ② If the engine has been repaired recently, there may be air in the injection drive pressure circuit.

  Allow the engine to warm up completely and operate it under load motor to remove air from the 

injection drive pressure circuit. 

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 ③ Compare the actual driving pressure and the required driving pressure on Cat ET. If the two 

readings 

do not exceed 2000kPa during the fault, it means there is a problem. The problem does not lie in the 

injection drive pressure circuit.

  ④ Check the seal on the injection drive pressure control valve. If the seal fails, replace the seal and 

repeat step ③. 

 ⑤ Check the wiring harness connected to the injection drive pressure control valve for open circuit 

and/or short circuit. 

 ⑥Measure the coil resistance on the injection drive pressure control valve. If the coil resistance 

exceeds (10±5)Ω, replace the injection drive pressure control valve. Note: Liquid that leaks out under 

pressure, even the size of a pinhole, can penetrate human tissue and cause serious injury or even death.

  If liquid is sprayed into the skin The skin must be treated immediately by a doctor familiar with this 

injury. Always use a wooden board or cardboard when checking for leaks.  

⑦Use ET to perform injection drive pressure excess test. If the injection drive pressure is low, there 

may be a leak in the high-pressure fuel supply circuit. 

 a. Remove the injection drive pressure control valve and unit injector connector plugs. 

 b. Use the ET and/or engine shutdown switch to stop the unit injector. 

 c. Remove the valve cover cover. d. When checking the drain port of the unit injector connector and 

the crossover cylinder seal for leaks, crank the engine. 

 e. Repair any leaks and repeat step ③. 

 f. If the injection drive pressure is still low during cranking, the pump compensator flow controller 

may 

be faulty. Pay equal attention to replacing the pump compensator controller assembly Repeat step ③.

6) Single fuel injector. 

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 ①Perform the injector solenoid test on the Cat ET to confirm that all injector solenoid coils are

 energized by the ECM. 

 ② Perform a cylinder shutoff test on the Cat ET to identify all cylinders that are not firing.  

7) Fuel supply. 

 ① Check the fuel pipe for the following problems: throttling, broken pipes and clamped pipes. If a 

problem is found with the fuel line, repair and/or replace the fuel line. Oil pipe. 

 ② Check whether there is any foreign matter in the fuel tank that may block the fuel supply.  

③When performing any procedures such as replacing the fuel filter, repairing the low-pressure fuel 

supply circuit, and replacing the unit injector, check whether there is air in the low-pressure fuel supply 

system. 

 ④ Clear the air from the low-pressure oil supply circuit. NOTE: The sight glass in the low pressure 

fuel supply line is helpful in diagnosing air in the fuel. 

 ⑤ Check the fuel quality. If the temperature is below 0°C, check whether there is solidified fuel (wax).

  ⑥When starting the engine, check the fuel pressure. If fuel pressure is low, replace the fuel filter. If 

fuel pressure is still low, check the following Components: Fuel transfer pump, fuel transfer pump 

coupling and fuel pressure regulator valve.  

8) Intake and exhaust systems. 

 ① Check the air filter throttling indicator. Clean or replace clogged air filter.