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John Deere – 1023E, 1025R and 1026R – Test Fuel Injection System

The purpose of this test is stop fuel flow to the cylinders (one at a time), while engine is running, to determine what effect that cylinder has on overall engine performance.

[1] – Park machine safely.

[2] – Remove air cleaner.

[3] –

Start engine and run at slow idle.

[4] –

Using two 17 mm open-end wrenches, loosen nut on one high-pressure fuel injector line, either at the injector nozzle (A), or at injection pump (B), while holding lower nut stationary with second wrench. Only loosen nut 1/8 of a turn (45°).

[5] – Listen for engine speed to drop and exhaust noise to change.

[6] – Tighten nut and allow engine to return to original speed before loosening next cylinder fuel line nut.

[7] – Compare sound and speed of each cylinder as it is disabled.

[8] – Tighten fuel line nuts and stop engine.


When fuel flow is stopped to a cylinder, engine rpm should drop, engine should begin to vibrate and run rough, and exhaust noise will be uneven until fuel flow is restored.

If test produces the results described, but engine performance remains poor, test the following:

– Clogged air cleaner elements, leaking air filter outlet hoses or clamps.
– Restriction in exhaust system.
– Presence of coolant or diesel in crankcase oil.

If defeating a single cylinder has no effect on overall engine performance, test the following:
– Fuel injector nozzle opening pressure, spray pattern, and leakage and for that cylinder.
See nozzle test.
– Cylinder compression or cylinder leakage test.
– Fuel supply pump pressure.
– Fuel shutoff solenoid is opening fully
– Fuel control and governor linkage flyweights allowing full fuel flow to injection pump.
– Injection pump timing correct.

If the test results are within specifications, remove injection pump and have tested at an Authorized Diesel Service (ADS) Center.