Item

Notes

Relevant Resources/Images

Primer Pump is leaking

This is a common source of air, and generally when you pump it you’ll see diesel coming out. The pump with the screw down top seems to suffer from this more.

The pump can easily be replaced.

A Bosch unit is preferable, the part number is “2 447 222 126”.

If the screw down style is being retained, ensure its left screwed in after use.

Fuel Sedimenter is rusted out, or gunked up

All 2H vehicles from the factory had a fuel sedimenter - these are meant to be drained of water occasionally but they rarely are, consequently they rust out, or restrict fuel flow.

The sedimenter should be removed, the float unscrewed and then the unit should be cleaned and inspected. Alternatively the unit can be bypassed to rule it out.

The location of the sedimenter varies by model:

• HJ60: Right hand inner side chassis rail, in front of fuel tank
• HJ47: Right hand inner side chassis rail - rear of the vacuum tank
• HJ75: Engine Bay mounted
• Coaster Bus: Not known.

Sedimenter images: https://photos.app.goo.gl/yTBd1qwecH7oP5L77

Gauze filter on Lift Pump inlet is dirty

This will cause a fuel flow restriction. Remove, clean, reinstall with fresh crush washers either side of the banjo.

Fuel Filter

Install a fresh fuel filter if the fuel filter hasn’t been changed in recent history.

I prefill fuel filters with Liqui Moly Diese Purge Plus, saves having to reprime, and may assist with injector cleaning.

If prefilling with an injector cleaner - ensure its of a type that can be run at 100% concentration and not a product designed to be added to a full tank of fuel

Never prefill a filter with a diesel from a jerry can or similar as you’ll be introducing unfiltered fuel into the clean side of the filter.

Filter Options (Spin on only)

• AC-DELCO ACF27
• DONALDSON P550057  
• FLEETGUARD FF5030  
• SAKURA FC8002
• Ryco Z169A

Flexible Fuel Line faults

There are flexible fuel lines that can have leaks or clamps missing/failed. All should be closely inspected for issues.

 The flexible lines are:

• Tank pickup to sedimenter
• Sedimenter to chassis hard line
• Chassis hard line to Lift Pump Inlet
• Injector return line to “T” on Lift Pump Inlet) - this is a very small hose that comes down from near the injector on cylinder 1 to the Lift pump, it comes down behind the injector pump and there is a length of soft line at both ends of a hard line.

Note that the HJ75 has a engine bay mounted sedimenter so the arrangement of soft and hard line is different in that model

If any doubt about hose clamps, replace them with brand new ones..

 Banjo Crush washers

Each fuel system banjo requires a crush washer either side of the banjo (copper or aluminium). If any banjo has been disturbed and the crush washers not replaced this is a likely cause.

Regardless if the banjos have been disturbed or not, crush washers are cheap and when chasing an air issue I generally just replace all of them.

There are 5 fuel system banjos requiring 2 washers each, they are:

• Lift Pump inlet
• Lift Pump outlet
• Fuel Filter housing inlet
• Fuel Filter housing outlet
• Injection Pump inlet
  
  

Location of Banjos.

Crush washers either side of a banjo.

Fuel Tank Pickup blocked

There is a small plastic filter on the fuel tank pickup which can get blocked.

I have also seen a blocked pickup hard line on a vehicle that sat for years.

Lift Pump Failure

If the lift pump has failed you’ll be significantly down on power and may think you have a sucking air fault. To confirm, crack the bleeder nipple on the fuel filter housing and crank the engine (preferably whilst cold so it doesn't start) - you should see good spurts of diesel at a fast pace.

The lift pump is shown below, it is bolted to the side of the injection pump and the “Primer Pump” screws into the top of the lift pump.

Here’s a video of a failed lift pump: https://youtu.be/Kk_862i004A

Lift pump rebuild kits are available or brand new lift pumps are not expensive.

Injector Return Line

If the return line has been disturbed (perhaps to replace injectors?) and the special return line washers were not replaced you may suck air through the return line.

The return line can also fracture, especially if injectors were removed and the line was rotated at all during removal of an injector line retaining nut.

Also note that the injector return line has a soft fuel line running from Injector #2 back to the inlet of the Lift Pump. This should be inspected for cracks etc.

Return line:

Return line washers:

Version

Date

Reason

1.0

22nd August 2024

Initial version

1.1

13th January 2025

Added information about soft injector return line

1.2

16th January 2025

Liqui Moly Prefill information

1.3

31st May 2025

Grammar/spelling

1.4

2nd August, 2025

Better instructions on fuel priming