How To Repair Denso Common Rail Injector- 100% Genuine

How To Repair Denso Common Rail Injector

  • At present, the technical and maintenance information of Denso common rail injectors is widely used and existing in the global diesel market.
  • The following document aims to provide a guide to using the tooling and shim kits together with genuine and non-genuine parts, to strip, rebuild and test Denso ‘G2’ type common rail injectors. Alterations to the shim adjustment of individual injectors were made and the results recorded. These results have been used to determine what effects any changes to the shim adjustment have on the overall performance of the injector.
  • Correction codes (QR codes) cannot be written and produced for any Denso injector using this information. The production and creation of QR codes requires complex software and intricate flow testing using genuine Denso/Hartridge authorised equipment. Denso Common Rail injector repair involves stringent clean room practices and very tight quality control on build tolerances. Please take this into consideration when attempting any dismantling of Denso Common Rail injectors.
  • Hopefully this guide will provide an insight into what can be achieved with tooling available outside of the Denso official repair programme. Consideration should be given to the importance of correction codes when undertaking any adjustment or unofficial repair of ANY common rail injector that uses a correction code.

Component Overview and Identification:

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

How To Repair Denso Common Rail Injector
Common Rail Injector
Common Rail Injector


  • The following dismantling, rebuild and test instructions are based on the use of the Common Rail 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

How To Repair Denso Common Rail Injector
  • 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).
  • e mechanical or electro-mechanical alternatives to conventional bearings that provide controllable shaft support through air, magnetic fields, etc. for critical, high precision applications.

STEP 2 - Valve Seat Removal

How To Repair Denso Common Rail Injector
  • 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, minimizing 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!
How To Repair Denso Common Rail 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 minimize 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.
How To Repair Denso Common Rail Injector
  • 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 tension 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.


Solenoid assembly

  • Resistance checks should be made to the solenoid. The specific resistance measured will depend upon the type of injector and should be compared to a new unit. The resistance recorded on the particular G2 injectors that we tested was approximately 0.5 -0.7 Ohms.
How To Repair Denso Common Rail Injector
  • Obvious signs of any damage to the outer casing or splits/cracks on the electrical connector should be observed. Check for erosion/corrosion of the electrical terminals and ensure that the inner surface of the solenoid is clean and free from dents etc (Fig13).
  • Ensure that the solenoid spring is in good condition. It may be a good idea to check and record the length against a new one.

Solenoid Valve and Half Ball Valve assembly

  • Check the condition of the solenoid valve assembly , paying particular attention to the half ball valve face and the seat inside the valve stem. The flat face of the half ball valve is responsible for sealing the control chamber, so it must be in good condition with no erosion or wear. These components are best inspected under a microscope. 
  • Check the conical seat that the ball seats on inside the valve, as well as the valve stem for any signs of wear, scratches and erosion (Fig 14)
How To Repair Denso Common Rail Injector

Renew both components if there are any abnormalities or doubt on their condition (both available from Diesel Distributors).

Valve Seat and Retaining Nut

Common Rail Injector
  • Inspect the valve seat for erosion and wear (Fig 16). As with the ball and valve assembly, this is probably best viewed under a microscope or other magnification equipment. If there are any marks across the seating area that would suggest a sealing problem-renew the valve seat (available through Diesel Distributors).
  • Inspect the sealing face of the retaining nut for signs of erosion and wear (Fig 16).
  • Due to the very fine tolerances involved in CR injectors, lapping of the sealing surfaces of these components is not recommended. Any attempt to lap the surfaces should be undertaken with the utmost care and with the use of VERY FINE lapping pastes.

Command Piston & Injector Body

  • Check the piston for scoring and wear marks along with the inner bore of the injector. If there is considered to be excessive scoring or wear on either component, then the unit will more than likely be scrapped (Fig 17). The piston should be clean, free from scoring and move freely inside the injector bore with no ‘snagging’ or tight spots.
How To Repair Denso Common Rail Injector

Nozzle Assembly, Pressure Spindle and Spring.

  • Guidelines for inspecting the nozzle assembly can be considered the same as for any conventional nozzle. Check for excessive wear or scoring on the needle shank and seat and renew the nozzle if necessary. (Genuine and non-genuine nozzles are available from Diesel Distributors, depending upon application and availability). Check the spring for condition and the spindle for excessive wear on the spring seat.


  • When re-assembling any common rail components, clean practices should always be observed and the utmost precaution should be taken to avoid any contamination of the components before and during assembly.
  • WARNING ‐ The torque values mentioned in the following procedure are a SUGGESTED VALUE based upon our experience and NOT Denso specification.
How To Repair Denso Common Rail Injector
  • Mount the injector in the holding jig and place the 2 locating dowels into their bores on the top face of the injector (these dowels are larger in length and diameter to the nozzle locating dowels). Ensure that the valve seat is the correct way round before inserting it into the injector. The bore on the underside of the valve needs to be aligned with the bore hole on the injector face (Fig 18 & 19).
  • Using the 3 pronged socket, insert and hand tighten the retaining nut into the injector with the sealing face towards the valve. Screw the guide over the socket, ensuring that the socket can still move, but with maximum support from the guide and tighten to 70‐75 NM (Fig 20).

STEP 2.2 – Solenoid & Solenoid Valve Assembly

How To Repair Denso Common Rail Injector
  • Fit the half ball valve into the solenoid valve stem and ensure that the flat face of the half ball valve is visible and level with the stem. DO NOT INSERT THE VALVE STEM INTO THE VALVE SEAT IF YOU CAN SEE THE SPHERICAL PART OF THE HALF BALL VALVE (Fig 22). IT MUST BE THE FLAT SIDE (Fig 21).
How To Repair Denso Common Rail Injector
  • The half ball valve should stay in the valve stem when turned over and inserted on the valve seat. Once the valve stem is in position ensure it is free by rotating it (Fig 23).
  • Place the fuel calibration shim on top of the injector (Fig 24)
  • Next, insert the solenoid spring shim and solenoid spring into the solenoid and carefully fit the solenoid onto the injector, ensuring that the spring seats in the centre of the valve and hand tighten. Once hand tight, tension the solenoid assembly to 10‐12 NM (Fig 25).

STEP 3.2 – Nozzle and Cap Nut Assembly

Re‐position the injector assembly in the jig with the solenoid towards the bottom

How To Repair Denso Common Rail Injector
  • Insert the command piston into the injector body with the main shank machined with grooves towards the solenoid end (Fig 26).
  • Next insert the nozzle opening pressure shim and the spring into the central injector bore and then insert the pressure spindle on top of the spring with the smaller diameter facing the nozzle needle (Fig 27.)
  • Insert the locating dowels into the sealing face and place the injector over them. Place the (new) cap nut over the nozzle and screw down until hand tight (Fig 28).
  • Ideally some kind of injector clamping rig should be used to unsure alignment of the nozzle, if you can find something or manufacture anything suitable to hold the body. The arrangement pictured below (Fig 29) features the Stanadyne Injector Aligning Too. 
  • An injector aligning tool was not used in this exercise and no operational problems were experienced, however it would be better to use one if available to minimise the risk of misalignment or b

FAQ of Common Rail Injector

  • When packing Common Rail Injector, it is essential to ensure that they are properly protected to prevent any damage during transportation.

    Here are some steps to pack Common Rail Injector effectively:
    1. Clean the parts: Before packing, make sure to clean the Common Rail Injectorthoroughly, removing any dirt, grease, or debris. This will help maintain the quality of the parts during transit.
    2. Use appropriate packaging materials: Select suitable packaging materials to protect the Common Rail InjectorConsider using sturdy cardboard boxes, foam inserts, bubble wrap, or packing peanuts to cushion and secure the parts.
    3. Wrap individual parts: Wrap each Common Rail Injectorseparately with bubble wrap or foam padding to provide extra protection against impacts and vibrations. This will prevent any scratching or potential damage caused by friction.
    4. Consider organizing parts: If there are multiple Common Rail Injector, we will systematically organize them. We will use small plastic bags or compartments inside the packaging to keep the parts separate and avoid entanglement or potential damage due to contact.
    5. Use proper sealing: Once the parts are securely placed inside the packaging, ensure the boxes are properly sealed to prevent any accidental opening or shifting of the contents during transit. Use strong packing tape to seal all the edges and corners of the box.
    6. Label the packages: Clearly label the packaging with appropriate shipping labels, including the recipient’s address, contact information, and any other relevant details.
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