how to repair denso common rail injector-2.

Component Overview and Identification:

The photo below shows an exploded stripped Denso G2 injector and labelled components:


The following dismantling, rebuild and test instructions are based on the use of the CR injector kit (part number – 850901) and Shim Kits (850276, 850296, 850301) available to purchase from Diesel Distributors, together with genuine and non genuine repair parts.

STEP 1 – Solenoid Removal

Figure 1    Figure 2    Figure 3

Mount the injector upright in the vice using the correct holding jaws, depending upon the body type and using the 27mm ‘crow’s foot’ gently loosen the solenoid (fig 1). Once loose continue to loosen by hand and CAREFULLY and GENTLY remove the solenoid, taking care not to drop the solenoid valve spring or tensioning shim (Fig 2).

Remove the ‘fuel calibration shim’ that will either still be sat on the injector or sat up inside the solenoid body (Fig 2).

The solenoid valve can then be removed using long nose pliers. TAKE CARE NOT TO DROP THE ‘HALF BALL VALVE’ (Fig 3). This is situated in the end of the solenoid valve. It is small and very easily lost!! – (Replacement valves and half ball valves are available through Diesel Distributors).

STEP 2 – Valve Seat Removal 

Figure 4    Figure 5    Figure 6

Insert the Three Pronged Valve Seat Socket into the guide (Fig 4), ensuring that the 3 prongs are located in the 3 holes in the valve seat retaining screw and then screw the guide over the socket. Tighten the guide all the way down by hand until it is felt to ‘bottom out’, then unscrew by approximately 1/8th of a turn (Fig 5). We need to ensure that the inner 3 pronged socket will turn, whilst maintaining maximum support from the guide, minimising the risk of the socket tilting.

WARNING – This nut is usually very tight!. Use a suitable breaker bar and a 14mm socket placed over the hex on the 3 pronged socket to undo the valve seat retaining nut (Fig 6). If unsuccessful, use an electric heat gun to apply GENTLE, MODERATE heat to the nut, then using the brass drift, strike the nut and re‐try. DO NOT USE A BLOW TORCH!! Excessive heat will damage the injector!

With the valve seat removed (Fig 7), carefully remove the 2 locating dowels (Fig 8). Remove the injector from the holding jig and turn upwards, whilst holding your hand over the open end of the body (Fig 9). The command piston should slide out, or at least begin to protrude from the bore. Withdraw the piston from the body. If there is no movement of the command piston at this point, it may signify that it is seized or tight. If this is the case, then it can be left in situ to be removed after the nozzle end has been dismantled.

STEP 3 – Cap nut Removal

Remount the injector in the holding jig with the nozzle assembly pointing upwards.

As with the valve seat retaining nut, the nozzle retaining nut can also be notoriously tight. One method that can be used to remove the nut more easily and minimise the risk of damage to the body thread and locating dowels involves the use of a pipe cutter to score the cap and ‘free’ the thread prior to removal. It is common practice to renew the cap nut on CR injectors anyway, so the cap nut will have to be discarded and a new one (available from Diesel Distributors) will be fitted on rebuild.

To remove the cap nut, score a line no deeper than 0.5mm approximately 15mm from the base of the nut (opposite to nozzle side) around the cap nut (Fig 10). Then, using a good 15mm single hex socket, undo the nut. There is a 15mm crow’s foot supplied in the kit, but this is best reserved for tightening, if using an injector aligning jig.

Once the injector cap nut has been removed, the nozzle can be removed along with the locating dowels (Fig 11). Finally, remove the injector body from the jig and carefully turn over, whilst holding the needle spring and remove the spring and spring tensioning shim (Fig12).

If the command piston was not removed earlier due to being tight or seized, then it can now be gently tapped out from one end. USUALLY, IF THE COMMAND PISTON REQUIRES FORCE TO BE REMOVED, THE INJECTOR BODY AND PISTON CAN BE CONSIDERED UNSERVICABLE AND NOT WORTH REPAIRING.