renault wont start
put new battery on ,new heater plugs, changed crank sensor,new fuel filter and still wont go its a 1.9 dci renault megane scenic sport alize.no diesel leaks anywhere but seems to be air in pipes still and kind find where from helpppppppppp .seems to start though if jump leads are on from another car ?compression?but when started doesnt miss a heart beat no splutter nothing perfect.also lifter pump is working.
Last edited by lundy; 19-02-12 at 14:50.
Probably the air in the pipes is due to an injector spilling back too much fuel due to a failed seal. When you switch on the ignition first time in the morning, the electric pump will force fuel up to the filter and on to the pump. If you watch and see continuous bubbles this suggests seal failure. The correct way to test is to do a spill back test or known as a leak off test.
When you use jump leads the increased cranking speed overcomes the air leak and it will start.
will give it a try tomorrow ,just one thing is it the seal where the injector meets the engine or where pipe joins injector,or is it a case of replacing all seals on injector ,then the next if it dont work and so on. thank you for reply.the test is done how by cracking off a injector ?know a bit about cars but this is new territory injectors.
Last edited by lundy; 19-02-12 at 21:13.
Your engine is a DCi which means it is a common rail fuel system. Instead of fuel being piped direct from the pump to each injector, your engine has a pump that generates fuel pressure and sends it to a large pipe known as the rail. From this common rail, pipes go to each injector. You need to understand that the pressure when you are cranking the engine is around 4,500 psi which can cause you serious harm if it is injected into your skin so safety first. Undoing injector pipes on this system - most engines are this type now - is a no-no. As soon as the pressure is reduced the various sensors detect this and usually shut the engine off.
The seals are internal and are a specialist job. The plastic top part of the injector more often than not breaks internally when removed and renders the injector useless. To check injectors you can connect to a diagnostic tool which can show a 'fuel quantity comparison'. This gives a graph of all 4 injectors and shows by how much above or below zero each one is actually injecting. This is the most accurate guide to the state of an injector.
However, the test called a spill back or leak off test also shows the state of the seals within the injectors. 4 small bottles are connected by plastic tubing to the injectors where the return pipes fit. Simply by watching how much fuel is sent to each bottle will determine if the injector seals have failed. If you have 3 bottles with 10% full and one that is 80% full then you have found the bad one. It is as simple as that really.
A lot of garages will not have this equipment even though you can get cheap kits from around £40 on eBay and most will not have the proper diagnostic tool. If you have a Bosch Service Centre near you or a good diesel specialist recommended by friends, then this is the best place to go. Also, these injectors can be really difficult to remove and often need specialised pullers.