A4 TDI Hot Engine Won't Start!!

Help! Wrong purchase?
Yesterday I picked up my new (used) A4 TDI PD 85 kW Avant Automatic. It's my first diesel car, and it pleasantly surprised me. HOWEVER: After parking it (after a 20 km drive), the starter motor turns the engine over, but it doesn't start. If you wait for 2-3 minutes and then let the starter motor run for 30-40 seconds (!!), it will start again.
I paid €15,600 for the car (77,000 km, manufactured in July 2001, with a complete service history and Advance trim). Should I insist on having it repaired, or should I cancel the purchase because it might turn out to be a major problem?
I've been tinkering with (gasoline-powered) classic cars for years, but I have absolutely no experience with diesel engines! Thank you in advance.
Doc Holliday.

If all the engine settings are correct, then the problem might be with the battery or, more likely, the starter.

If the engine doesn't reach its required starting speed, the warm engine won't start! The cold engine isn't affected by this, because the fuel injection timing is adjusted to compensate, and a lower starting speed is required!

Simply disconnect the coolant temperature sensor plug when the engine is warm. This will simulate extremely cold temperatures. If it starts up immediately, then my suspicion is confirmed!

It could also be the coolant temperature sensor!

Therefore, it's best to first have the error memory read out, and ideally also include the measurement data blocks!

Regards,

Manuel.

Hi Manuel, thanks a lot for the tip!
I've already ordered some workshop manuals for the A4, but they haven't arrived yet! That's a question for beginners: Where is the coolant temperature sensor located? (It's a bit unpleasant to blindly search around in the dark when the engine is hot.)
The error memory was read out at the workshop 3 days ago, so I think it's more likely to be the speed sensor than the connector.
Thank you very much.
Doc Holliday.

At the rear of the cylinder head, there is a distributor flange for the coolant. There he is!

But since you still have a warranty, I would take it to the workshop.

Regards,

Manuel.

Okay, so if you bought the car from a dealer, then the dealer should fix the problem, and you should have a warranty (usually 1-2 years, depending on the contract).

Hi, thank you very much for the tips!!
Sure, I'll bring the box back to the workshop tomorrow. However, after having already browsed your forum last week, it seemed to me that it was urgently necessary to keep the guys from VAG busy with specific tasks. Furthermore, he also has the problem that after a short sprint with several gas changes at approximately 50-70 km/h (not at full speed on the highway!!), the engine cuts out while driving when he releases the gas. So, the guys will definitely have something to do!! I will soon lose a sentence, and then you'll know what it was about.
Again, with all my best wishes!
Doc Holliday.

Hmm, maybe it's the famous Relais 109 (if it even exists in that car).

Best regards, WarLord.

Hello Doctor,

If you have starting problems again, check if there are any air bubbles in the clear hose connecting the fuel filter to the injection pump.

Best regards, Rainer.

Rainer K. wrote:

whether there are air bubbles in the transparent hose from the diesel filter to the injection pump...

Hi Rainer,

Doc is writing about an 85 kW = PD motor.
Does it also have a clear hose, for example, from the filter to the tandem pump?

Normally not... only the VEP diesel locomotives.

Julian wrote:

Normally not... only the VEP diesel locomotives.

Hi Julian,

son Krampf - because drafts probably wouldn't be well-received by people with PDs either...

Okay, so I already have another DIY project for my future PD-Polo, in addition to the LDA!

Hello,

Sorry, I think I got things mixed up... I was thinking about the motor with VEP (Variable Valve Timing).
Thank you for the correction!

Best regards, Rainer.

Hello, the tandem pump has a filter, and it will likely cause problems soon if it gets clogged. Also, there's nothing mentioned about cleaning it in any of the inspection procedures.
I think most people don't even realize that one is installed there.

Attention!!!!!!!!!!!!!! Solution to the riddle (see above).
I picked up the car from the repair shop today, and it starts like a rocket, whether it's cold or warm. There's no more hesitation when I release the gas pedal, so basically, the problem is solved!
Cause: A faulty check valve in the vacuum fuel pump. This means that when the engine is stopped or experiences a sudden load change, the fuel reservoir can run empty, and that's it.
To everyone who helped me: thank you very much!
Doc Holliday.