Starting problems with the 2.5 TDI - SOLUTION!!!

Hello everyone!

'Some time ago, I reported about starting problems that occur in the Audi A6 2.5 TDI (engine code AAT), manufactured in 1994 (model year 1995) (see my other topic).'

After a lot of pondering, I've finally figured out the solution and the explanation!
Okay:
1.) Is it possible for the gear on this engine that drives the timing belt and is located on the crankshaft to start wobbling? This would misalign the injection timing, which could result in a small puff of black smoke during the initial startup.
2.) With mileage exceeding 100,000 km, the plastic of the pulley may tear due to friction from the timing belt. Fault detection: slight jerking during start-up – also simulates minor fuel injection problems!
3.) If the fuel injection pump is misadjusted, a good battery might temporarily compensate for it. HOWEVER, THIS IS NOT A LONG-TERM SOLUTION. My advice: Repeatedly charge the battery until the pump is working correctly again (e.g., have it serviced by BOSCH).
4.) In rare cases, it's also possible that the injectors are clogged, which can be noticed by a lack of power. This too can cause starting problems.

reasons why it only happens on the first start:
'If the battery is already a bit weak! = Slow engagement of the starter!'
In the second attempt, everything works fine because the combustion chamber is already warm from the previous explosions, so a less extreme compression is required.

So, I hope I've made some of you happy!!

Morph.

Quote:

1.) Is it possible for the gear, which drives the timing belt and is located on the crankshaft, to start wobbling in this engine? This would misalign the injection timing, resulting in a small puff of black smoke during the initial startup process.

Yes, a loose timing belt pulley can affect the injection timing. Was it loose in your case, and how was it reattached?

Quote:

Duch den verstellten EPunkt braucht der Motor länger um die Kompression zu erreichen.

Hmm, that's nonsense.

What was the exact cause of the starting problems in your case? Was it a misaligned injection timing due to a loose camshaft sprocket, or faulty injectors?
Falls Deine Einspritzdüsen nicht unter normalen Verschleiß litten (wieviel km hatten sie drauf ?), würde ich mir an Deiner Stelle mal Gedanken machen woher die verstopfen können. Durch Dreck aus dem Tank nämlich nicht, dafür ist der Dieselfilter da.

Best regards, Rainer.

Hello,

Just a quick question:
What is the relationship between the battery's state of charge and fuel injection accuracy?
What can the ESP do? (Of course, if the battery is dead, it won't work at all, but there are also other causes.) [/quote]

Hello Rainer!

Sure, here's the translation:

'Yes, it was also loose in my case. Since I only had about 5,000 km left until the timing belt needed to be replaced anyway, it was actually discovered by chance and immediately changed!'

Unfortunately, a clear cause could not be determined in my case!
First, I suspected a faulty coolant temperature sensor, which is cheap, but unfortunately, it didn't fix the problem.
After that, I suspected the nozzles. However, replacing them seems to have made an improvement!
As a last resort, I had the pump serviced – and while it was being done, I also replaced all two timing belts and the serpentine belt. During this process, defects were discovered on the nose of the pulley as well as on the belt sheave! Also, the pump was misaligned in my case, but otherwise showed no flaws.

The only thing I didn't expect was that the battery I bought a year ago had already been significantly degraded.

Translation:

Regarding the previous statement, I apologize for the error. The lack of compression wasn't due to the EPunkt system, but rather a slow-acting starter motor. This is being corrected – sorry!

Hi Michael II!

Absolutely no accuracy!
but: If the pump is only slightly misaligned, a good battery, like mine once was , can still provide enough power to start the starter motor and thus start the engine quite well!

Unfortunately, the battery was gradually weakening, which I didn't notice because I suspected the problem was somewhere else! (see my reply to Rainer).

Another question for everyone!

Does this happen often, that the vibration damper on the pulley fails?
That thing isn't exactly cheap!

According to Audi, it's in there for life! Joke or not?

Morph.