John Deere — Test Fuel Supply Pump (MICO in-Line Injection Pump)
Testing & diagnosis
From a John Deere service manual — check it applies to your exact model before use.
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Before you start
- Serious injection pump or engine damage could occur if enough diesel fuel leaks past tappet and seal
Procedure
- Connect compressed air line to a pressure gauge and to supply inlet fitting; air line should have a regulating valve
- Cap or plug supply pump outlet fitting
- Submerge supply pump in a container of clean diesel fuel and regulate air pressure to 200 kPa (2 bar; 29 psi)
- Move tappet in and out by hand and observe for air bubbles around tappet
- If bubbles appear, seal is defective or tappet is worn
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Regulate air pressure to 200 kPa (2 bar; 29 psi)
Source: John Deere service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.