2H Diaphragm Replacement

Version: 2.5

Author: Duncan Margetts

Source URL:

https://docs.google.com/document/d/1ZPvljDvzPpgPWnViWyJdNVVkYDdpIe9x_ppJcHW3jX4/edit?usp=sharing

Symptoms of a broken Injector Pump Diaphragm on any vehicle with a 2H, H, B, 2B, 3B (with inline pump) Engines such as HJ45, HJ47, HJ60, HJ75, BJ60, BJ40, BJ42 and some Coaster buses:

• High Idle
• Poor throttle response
• Excessive exhaust smoke under a variety of load conditions
• Excessive exhaust smoke when engine braking        

Diaphragm Part Number: DENSO 090580-0041, Toyota 22303-47010

Potential Suppliers:

• Daniel Dietrich (Technical Motor Sports) https://technicalsportscorner.com.au/products/b-3b-h-2h-injector-pump-governor-diaphragm-denso-box
• Terrain Tamer Australia. Part Number 22303-47010, Ph. 1300 888 444
• Denso Stockists
• EBay - search on “HJ47 diaphragm”

Tools required:

• Medium size flat bladed screwdriver
• Pair of needle nose pliers

What the diaphragm does:

On almost all diesel engines the throttle (accelerator) is connected directly to the injection pump, the throttle directly controls fuel flow to the injectors (and thus controls the engine speed). The intake manifold is left wide open, there’s no butterfly controlling the intake of air to the engine.  The Toyota 2H Engine is a little different as it has a butterfly in the intake manifold that is controlled by the accelerator. There are two vacuum hoses connected from the intake manifold to the Injection Pump, one from before the butterfly, and one from after. As the Driver changes the throttle position the intake butterfly moves and a vacuum differential occurs between the two vacuum hoses. This vacuum differential acts on the diaphragm in the Injection Pump.   When very little fuel is required (closed butterfly) the diaphragm is pulled towards the back of the pump and the fuel control rack is moved to a minimal fuel position.  When more fuel is required there is less of a vacuum differential between the two hoses and the large spring behind the governor cover pushes the fuel control rack towards a position that delivers more fuel. Its also possible that the two hoses from the Throttle Body to the Governor housing can break.. Check these are intact before proceeding with changing the Diaphragm.

You do NOT need to remove the pump from the engine to do this job (don’t even consider removing the pump)

Step 1: Remove the governor housing cover, 4 flat-head Screws retain it. The screw on the top right of this image may be lock-wired in place. Also note that it's slightly different from the other three screws and it should go back in the same place.  Don't be surprised if a small amount of engine oil comes out, this is normal. You may wish to place a rag underneath the housing prior to opening it.

This is where the governor housing cover can be found on the pump:

Step 2: Remove the governor housing cover to expose the diaphragm. A large spring and some shims will be behind it so be sure to retain these for reinstallation. After you’ve removed the cover the pump will look like this, the diaphragm is circled. The cover will be retained by a small rubber hose that is connected to the Intake manifold. You can remove this hose in order to move the cover right out of the way.

Step 3: Using a pair of needle nose pliers, pop the diaphragm forward out of its seat.. you will not be able to remove it from the pump yet though:

This is what the rear of the governor housing cover and the spring looks like once removed:

Be careful not to lose the shims that sit behind the spring, there may be 1-4 of them depending on how the pump was calibrated. They look like this:

Step 4: Reaching behind the diaphragm pull out the small split pin and washer that retains it on the Fuel Control Rack.. there is a tiny washer behind the split pin, try and recover it without letting it drop. If either the split pin or washer drops into the pump, don't panic, it can be retrieved with a torch, small mirror and a magnet.. It's preferable that it's caught though:

Step 5: After the split pin is removed the diaphragm should be slid away from the engine side of the pump in order to remove it from the housing,. The red line below shows the shaft that the diaphragm slides onto:

This is what the removed diaphragm looks like from behind. The red line shows the hole that the shaft above sits in..

Step 6: The new diaphragm can now be installed . Slide the new diaphragm onto shaft, taking note that it must be the correct way up, there is a small tab on the bottom of the diaphragm that must line up with the corresponding small divot in the bottom of the governor housing as shown in the two photos below:

Step 7:

• Reinstall the small washer on the shaft (you need to reach behind the diaphragm to do this)
• Reinstall the split pin (you need to reach behind the diaphragm to do this)
• Seat the diaphragm securely into its seat, aligning the tab at the bottom with the divot in the seat
• Reinstall the governor housing cover, along with the large spring and the shims that were behind
• Secure the cover with the four flat head screws, remembering that the one on the top right (furthest away from engine, top) is slightly different from the others
• Reattach the vacuum hose to the top of the governor housing

Step 8: Job complete. Start the engine and test that:

• Throttle response is normal
• Idle speed is normal
• After higher revs ensure that the engine quickly returns to idle speed when the throttle is released

Footnote 1 - Relevant Page Factory Manual (1 of 3)

Footnote 2 - Relevant Page Factory Manual (2 of 3)

Footnote 2 - Relevant Page Factory Manual (3 of 3)

Footnote 4 - Governor Housing Drain Plug

When servicing your 2H.. You should also occasionally drain the governor housing of accumulated engine oil. There is a drain screen for this purpose shown below. Remove the screw and allow any accumulated oil to drain out. A small screwdriver could be used to encourage any particularly thick oil to start running out. An accumulation of oil may result in hard starts.

Footnote 5 - Description of Rack movement

Footnote 4.

There’s a good video of a 3B pump having its diaphragm replaced here:

https://www.youtube.com/watch?v=HQB2qzbpP48

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