Hot start issue with MK5 Golf 2.0

[jdd]

Just wondering if any of the diesel experts on here have come across a problem with the MK 5 2.0 TDI whereby it takes a lot of cranking (10-15 sec) to start after it’s warm.
The problem never happens when cold, or if it’s been sitting for more than about an hour after being driven. At first it was intermittent but has gradually got worse and now happens almost every time.
It doesn’t appear to be a battery problem as it cranks as fast as it ever did.
The car has about 72,000K’s on it and has never had a problem until now; although once it’s running it runs well so it only appears to be a starting issue.

Any ideas ?

[Greg Roles]

Sadly it can be several things. My bet is the battery age. I have had starting problems when my old battery started to struggle, and the crank speed sensor, a smalll sensor that watched the flywheel, didnlt see the right sort of cranking revs ( approx 250rpm ). It still "seemed" to be cranking OK, but even to this day with a brand new top end battery if it has just been driven and has a good charge it fires up instantly, but if I leave it a good week, and the charge drops just a little, it takes a few more turns to fire. If you can borrow a battery charger, give it a good charge, and see if the problem continuues then you are onto the next step, and that's your coolant sensor. This obviously tells the engine if it is hot or cold, and alters both the glowplugs, and the amount of fuel injected on startup. These things were docey in the former 1.9 TDI frm what I read, and the ECU programming on these earlier engines was a major culprit of hard hot starting after they got some miles on them. You may find that simply disconnecting your coolant sensor and the problem will go away, and you need a new one.

The final problem may be the EGR flap is sticking due to the typical oil blowby sludge, and without a good supply of air, a diesel is going to struggle to start. It's an outlyer in my opinion, but as I see it happening so frequently, it could be an issue. When was the last time you cleaned the EGR valve??

[buzuki]

Could be poor injector seats, causing air to get in lines once hot.

Is a known problem on 2.0L tdi. Ive also had it happen on a 2.5L. I didnt believe it at first but i fitted clear feed and return lines, and sure enough there was air in the return line. I removed injectors, fitted new seats, and problem fixed.

[gldgti]

yeah, nomoatter what diesel engine it is, long cranking times when hot is usually air in the fuel supply lines.

[jdd]

Thanks for all your replies so far, at least this has given me a few things to look at.
I’ve got a reasonable amount of experience but not on diesels, but I’m learning !

I will do some investigation and report back on what I find.
It may not be for a little while as I’m fairly busy with work at the moment and this vehicle doesn’t get driven all that often at the moment.

[ryanp]

We see this problem on just about every TDI we have in to work on. Starts on the button when flat cold, but when warm they really struggle.

99% of the time it is a faulty 2 PIN Coolant Temp Sensor - VW Part Number 06A 919 501 A. There are two on the 2.0 TDI, one on the side of the engine (you have to remove the Airbox to get to it) and one on the Thermostat housing (very front of the Engine).
As Greg Roles said, try removing the plug to see if the problem goes away (only temporary though!).
I have also had a Leon 1.9 TDI with similar symptoms and it was the Fuel Temp Sensor.

Please report back with your findings.

Ry