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]

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.:getmecoat:





.

[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. :D

[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 )

[marinabrian]

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

It is in the OP's original description Rob, the car sometimes starts if bumped, so the cam sensor will be ok ;)

He's changed the crank sensor, unnecessarily and the symptoms are right up there with injector leakback which is why Mike suggested it.

I have seen cars with excessive leakback start when "jumped" as the extra oomph supplied to the starter spins the engine that little bit faster ;)

Leakback is also more evident when the engine is warm, as the fuel oil is less viscous and leaks more readily past the valving in the injector.

Brian :D

[Boulton85]

Well just on the off chance I took the camshaft sensor out and put it in the fridge to cool it down but no joy so it's looking more like the injectors :mad:

[Boulton85]

Well just had the test done and it turns out that 2 / 4 are leaking

[Mike Noc]

You can get them reconditioned to save on the cost of buying new ones Marc. Lynx Diesels have often been recommended on the forum, although I haven't used them myself.

[Boulton85]

Yeah found some close to home at a company called firth diesel injection £110+vat each exchange units

[MrDoodles]

Not being a diesel expert, but as the other injectors have done exactly the same mileage as the one's that are leaking, what's the perceived wisdom from the experts on the site about replacing all of them, rather than just the two that are currently leaking? :shrug:

[Boulton85]

I'm guessing they some the same mileage but keeping the cost down if this fix's the issue then I can change other two ata later date

[Boulton85]

Got 2 reconed / exchange units with a years guarantee £182.40

[Boulton85]

Well injectors are here so going to fit them tomorrow 😊 I'm
Not sure if car down on power etc as its my first one and it feels the same as when I picked it up so if I change the injectors will I feel a difference?

[Mike Noc]

Wouldn't have thought so. A failing MAF can cause the engine to feel sluggish. It will also feel the same if it is a 116. 135 feels better, and the 160 bhp remap is the way to go. :}

[Boulton85]

Mines a 135 but doesn't feel all that quick to say it's all so got a synagy tuning box on

[Boulton85]

Just changed the 2 injectors took me an hour not bad considering Iv never done anything with a Diesel engine.... Only thing is it's still got a judder on tick over

[bl52krz]

Give it time to bleed. Then take it for a short drive.

[Boulton85]

Been running the car now for a few days and done 500miled in her and she still juddering on tick over any ideas