2.5 TDI cold starting still not good

[allankennedy]

Although I have replaced all 6 glow plugs on my 2005 Allroad (yes all 6 were open circuit!) cold starting is still not as it should be.
(Please see my post 2 weeks ago where I have described the job done) When the ambient is 4c or more then the engine will start first time but when it is any colder it really struggles to get going. Whilst I had the plugs out I checked the supply to them with a test lamp which was staying on for about 10 seconds so I am sure the problem is not with the relay etc:

I have tried the old trick of switching on the ignition twice to allow the glow plugs to get hotter, but still I have to keep the starter going for a prolonged period whilst the engine begins to fire, seemingly on one or two cylinders. When it eventually picks up then it runs perfectly. In fact the engine is absolutely spot on except for this issue.
Other diesel engines I have owned (Mercedes and Jeep) have always started very easily no matter how cold, so is this something unique to the Audi 2.5tdi ?

 

[quattrodave]

I've got a 2003 a4 2.5 quattro and it starts On the button every time, hot or cold. Glow plug light stays on for about 4-5 secs when cold then its away....
Have you checked the injection pump timing ?
Apparently this can cause cold starting issues if its not within spec

 

[allankennedy]

No I haven't checked the fuel pump timing and frankly, I don't know how so I'll ask a mechanic friend tomorrow. I can't help thinking though that such a problem would affect the way the engine runs generally and, as I said, once it gets going it drives perfectly. No misfiring, very fast and responsive etc etc

 

[PAULF]

You need to use software such as VCDS to check your pump timing whilst the engine is running.

Please don't randomly change parts or you will spend a lot of cash and not solve the problem.

Read up on the fault here, and elsewhere and methodically progress though checks.

Most likely causes are injection pump timing, injection pump advance solenoid, Coolant Temp Sensor (CTS), glow plug timing (adjustable with VCDS).
When it's running and up to temp check the cylinder balance with VCDS to see if there is one or two cylinders out.

That should get you heading in the correct direction at least.

 

[All-rod]

When it's running and up to temp check the cylinder balance with VCDS to see if there is one or two cylinders out.
That should get you heading in the correct direction at least.

You mean like this one?



I always think this is pump/ fuel system related.

 

[darysas]

like this
Volkswagen tdi 2.5 timing test - YouTube
must go not through mesuring bloks, but through basic setings, group 4 and tdi timing, then chuose engine code, yelow line must be on blue our little higer near green.

 

[darysas]

different between cyl is out of range, and injected quantity on idle is to high, i see temp 89c, suo it should be 4,5-6. and yuors 7,5 it means that ecu injecting more fuel than tipicaly, the reasons may be fueal rate in ecu or mechanickal like nozzle wear out

You mean like this one?

View attachment 28162

I always think this is pump/ fuel system related.

 

[All-rod]

Thanks, thats exactly what I always thought. pump and injector time...

 

[audi2.5tdi]

my fuel IQ at idle is currently 11.5 - 14!!

i did pick up a new timing piston from Bosch on Friday to fit tomorrow

mines a pig to start all the time, cold or hot, left a few days or stopping for 3 mins in a fuel station, prelonged cranking, sounds like its started on fewer than the 6 cylinders and you have to keep cranking untill it sounds like its running on 6 or it just cuts out

injection timing bang on in VCDS so hopefully this will solve my issue

 

[All-rod]

This would very likely also mean that there by now is some excessive wear on cams or that air is getting in to fuel lines.
Since replacing glow plugs mine starts much better, but just does not run right for one or both of other two reasons.
I doubt that timing piston would change much.

 

[PAULF]

Do remember to make sure the aircon is off and the engine is up to temp.
You get a couple of mgs difference with loading on the engine - although not as high as 11-14!

I would suggest No 2 cylinder is the problem , as all the others are trying to keep up with it!

 

[jonbonb]

I had a similar problem to this it turned out to be the oil temp sensor, it was telling the ecu the oil was at -40 degrees so the glow plug light would stay on for 4-5 sec and then take prolonged cranking to start as the car was trying to warm up the oil before starting.

New sensor and starts on the button now without fail.

Just an fyi for anyone experiencing similar.

 

[audi2.5tdi]

mine was the piston, replaced the timing piston in the fuel pump and the car is 100x better, starts on the button, hot or cold, and IQ is back down in the proper range