1997/05/27 Caterpillar

Procedure To Investigate Misfires On Engines Equipped With Electronic Unit Injectors (EUI){1290}

Usage:

3176B (9CK),
C-10 (2PN),
C-12 (1YN),
3406E (5EK, 6TS) Truck Engines

These truck engines are equipped with EUI's. Investigations of engine misfire complaints indicate that some misfires are actually due to faulty connection of the wiring harness to the EUI.

1. If a misfire is present, use the electronic service tool to perform a cylinder cutout test to isolate the misfiring cylinder. Use an 8T-8697 Electronic Control Analyzer And Programmer (ECAP) or Cat Electronic Technician, JERD2125.

Illustration 1. Location of posts (1) on unit injector.

Illustration 2. EUI Wiring harness assembly wires (2). EUI connector (3).

Illustration 3. Nuts (4). Cap assembly (5).

2. If a misfiring cylinder is found, check the connection between the wiring harness connector and the EUI solenoid.

A. Loosen two nuts (4) on cap (5) and remove cap (5).

B. Remove connector (3) from posts (1) on EUI solenoid.

C. DO NOT remove EUI from cylinder head. Clean and inspect the threads on posts (1). Be sure the threads are free of any damage or distortion which could prevent the free tightening of the nuts (4).

D. Check to be sure wires (2) are secure in connector (3).

E. Put connector (3) in position on EUI post (1).

F. Put cap (5) in position and tighten nuts (4) to a torque of 1.7 ± 0.25 N·m (15 ± 2 lb in).

NOTE: Each nut (4) must be tightened to the correct torque to ensure that the connector (3) does not become loose. If the connector becomes loose during engine operation, electrical "arcing" may occur on the solenoid posts (1). This may cause a misfire or a misfire related fault code to be generated by the engine control module (ECM). This does NOT indicate a faulty EUI.

G. Recheck for misfire symptoms. Replace the unit injector ONLY if the misfire persists and after other probable causes for the misfire have been ruled out.