Cdti warm start issue

[Boulton85]

Hi all Iv been looking for a thread on warm start issue. Iv got a mgzt 2.0 cdti done 150000 just changed the crank sensor still no go it will fire sometimes if you bump it. Iv been told to run a leek back test which is my next job, but wouldn't I have more issues if the injectors were leaking? Any advice and help would be appreciated

Cheers marc

[super s]

the fuel pumps are common to fail...

i would look over there first...

do you ear them work when you push the key position 2...???

[Boulton85]

Yep both pumps are working fine.

[Mike Noc]

Originally Posted by Boulton85

Iv been told to run a leek back test which is my next job, but wouldn't I have more issues if the injectors were leaking? Any advice and help would be appreciated

Cheers marc

This can be a sign of one or more leaking injectors. The reason you don't see anything else wrong is that when starting, the engine driven high pressure fuel pump is only rotating slowly and can't supply enough pressure to the fuel rail for the ECM to start firing the injectors.

Once started the pump speeds up and then it can keep the rail pressurised.... until the leak gets too bad.





.

[Boulton85]

Ok so why dosent it struggle when cold surely if the injectors are leaking then it should effect it when it's cold.... I'm not to clued up on Diesel engines I'm more of a Honda nut but I love this car so really want to sort it.

[Mike Noc]

Probably a combination of the HP pump tolerances being tighter when cold and the fuel oil being a bit thicker.

[Boulton85]

I can't see how if the engine is cold or hot it will only effect the injectors when hot, if the injectors are faulty then they would cause some kind of issue when cold or warm not just warm! If it is the injectors then wouldn't I can smoke out the exhaust and it been a bit more noisier?

[Mike Noc]

As mentioned it is because you aren't getting the minimum fuel pressure required at the rail when cranking. The fuel oil is thicker when cold so it won't leak away as quickly as it would when hot.

It won't cause any other symptoms because the fuel is leaking back to the tank via the spill return line.

Best thing to do is carry out a leakback test, and then you can either confirm or rule out the injectors being the cause.

[Boulton85]

Thanks for the help its booked in for a leak back test next week! I only asking these questions as not sure bout Diesel engines

[trebor]

the cam sensor has not been mentioned so far unless i have missed it, that is often the cause of warm starting issues for the diesel, so have your leak back test done and if thats ok that would be my next call ( do a search on cam sensor and you will find lots of threads about it )