Engine Starts easy when cold but stalls after a short period.

1. Air Leak in Fuel Line / System

Diesels are very temperamental when air enters the fuel system.

Need to discuss / expand:

a. Fuel Hoses from fuel tank into Fuel Fitler and from Fuel Filter to Diesel Pump.
b. Sender and Return fuel hoses at the fuel tank end and how air leak can occur there.
c. Diesel Pump Return line/hose
d. Fuel Spill Over Pipe (small pipe interconnecting Injector spill rail back into the injector pump).
e. Bleeder screw on fuel filter / primer not sealing
f. Fuel filter not sealed onto primer
g. Fuel filter water sensor not sealed or the drain screw not sealing
h. Fuel Primer itself can be a source of air leaks via the hand pump.
i. Fuel Pickup pipe corroded within the tank can allow air leak
j . Fuel Pickup Filter and by pass can be blocked / dirty.

See my previous post "Air leak in Fuel Line / System".

2. Injector Pump

The injector pump has several seals that can and will perish over the lifetime of a diesel engine. However alot of recent failures with diesel engines has been caused by the reduction of sulphur in diesel down to 500 ppm and based on articles that I've read, it is being considered by the fuel / oil companies to reduce it further down to 50ppm. This is were its a little grey for me in that I believe that once you have the seals replaced the seals will be fine on 500 ppm, the failure is caused by the change in fuel mix environment where seals have been conditioned to the higher sulphur levels, but when the sulphur was reduce (less lubrication) it cause them to fail.


My understanding after reading articles is that when the pump seals perish, even though the fuel with in the pump is under a fair amount of pressure, you may not get any tell tale signs of diesel leaking from the pump. So if you inspect the diesel pump and can see a diesel leaking (or if the seals are truely gone - pissing) out of the pump then chances are this could be your source of an air leak within the fuel system.

There is one more seal issue that should be noted here and that is the BIG seal where the pump drive gear bolt together to the engine) that can allow diesel to leak internally into sump / engine block and allow oil to leak into the pump, allow oil to be burn upon a cold start up after the engine has been allowed to stop / lay for a while. Obvious signs to look for is if your oil level increases significantly and or you start find oil within the fuel filter and possibly injectors, you may need to cut open your old fuel filter and check it that way.


3. Possible Heating / Glow Plug Issue

With modern Diesels engine I've read about how they can with reasonable performance start with compression even at low temperatures. So don't overlook them as a potential source of the rough idle at start up. Remember that glow plugs are used to help start the engine but also to help initial running until the engine gets to a normal operating temperature or the max glow plug module time out.

Need to Expand on the following:

a. one or more glow plugs faulty or no longer effective

b. glow plug relay stuffed, hence preventing power to the glow plugs

c. Engine Sensors (i.e. temperature sender) may be stuffed or faulty causing the Glow Plug control module to prematurely shut off. Also the wiring between the sensors and the Glow Plug Module / Control.

d. Glow Plug Module / control itself could be faulty (i.e. capacitor controlling the timing circuit are a known issue on the Pajero's).

e. Depending on your Glow Plug system you may have two Glow plug Relays such as that in the Pajero 2.5ltr has a 12v for initial heating and star then a 6v relay for initial running.

f. Poor wiring / electrical connectivity between relay and glow plugs.

g. Busrail / bar in poor condition hence not providing glow plug with current to heat up.

h. Wrong glow plugs for the vehicle.