ALH Engine Problems: Common Issues & Fixes

Hi,

Currently, there are two Audi A3 vehicles with ALH engines exhibiting the same symptom: they start more poorly when warm than when cold. In one case, the problem occurred after replacing the diesel filter, and in the other, after a timing belt replacement.

Both have impressive performance values in the pump settings!

However, it's noticeable that, in my opinion, there are a surprisingly large number of air bubbles visible in the transparent fuel line.

The other one also has extremely minimal markings, but they are only visible at the transition point from the black, ribbed section to the transparent fuel line. Perhaps they are just swirls? It's definitely not the case with the first one, but where did they suddenly come from?

With the version without the bubbles, I had some time to experiment, and here's what I found out:

- If you disconnect the temperature sensor, the engine will start immediately, even when warm!
- If you reprogram the engine control unit (ECU) from an automatic transmission back to a manual transmission, it will likely start misfiring again.

If it were a Sharan, I'd suspect the starter motor, but could it also be the starter motor in an A3?

Both vehicles are from the year 1999 and both have an ALH engine.

Are there any values that are important to check?
Or any really good tips (I've searched a lot, found things, and read them, but nothing has helped 100%).

Chrisi.

Hi.

Are all the cables between the battery in really good condition, with no kinks and the connections tight?

Are the batteries charged?

"A ZR (Zündreihenfolge) change is always a warning sign... Ideally, the pumps should be within the basic adjustment tolerance range as early as possible, as anything outside of that range often noticeably worsens the warm start performance."

Hi,

Batteries were tested and replaced, but there was no change!
All the cables look great, but I've checked them all again, cleaned them, and used contact cleaner -> STILL NOTHING.

According to the tester, the pump is noisy, but is set to within 0.02% of the ideal operating parameters.

Disconnect the fuel pump and let the engine crank. The starter motor is running at 240-290 RPM.
Could it be?
As I said, if it's running in automatic mode or if the coolant temperature sensor is faulty, it starts up much better!

Chrisi.

Hello,

Have you ever read the temperature values from the coolant temperature sensors with the engine warm?
I mean, are the values plausible? In my A3 from 7/98 with the AHF, I actually already replaced the temperature sensor because it sometimes provided strange values in the temperature range around 5°C during cold starts.

Best regards, Rainer.

vagtuning wrote:

Disconnect the pump and let it spin, the starter motor is running at 240-290 RPM. Could it be him?

Hi Chrisi,

It seems a bit too slow to me, with a speed of less than 300 rpm.

Okay, I'm ready. Please provide the German text you want me to translate.

Hi,

'An improvement was achieved by installing an aftermarket diesel filter, for some reason. The original filters have a strange plastic disc under the preheating valve, which the aftermarket ones don't. The improvement was noticeable, but it's still not perfect yet!'

Information Department: THIS CANNOT BE!!!

- If you disconnect the temperature sensor, the engine will start immediately, even when it's warm!
- If you reprogram the engine control unit (ECU) from automatic transmission to manual transmission, it will likely start misfiring again.

Since I'm not very familiar with the 'digital aspects' related to STGs,
I wanted to ask here why the automatic coding of the engine control unit (ECU) is used in vehicles.
not generally used for addressing warm-start problems with manual transmissions.

Best regards.
peter

Because after a certain amount of driving, the car exhibits driving performance issues, as the engine control unit is not receiving information from the transmission.

Are these handling deficiencies already known, and how do they relate to...?
Bad warm start with excess weight?
I will (assuming I have access to a software version that supports it).
Recoding my car's (Ibiza, Seat, manufactured in 1998) Automatic Fault Notification (AFN) system from manual to automatic.
and post the results, if necessary.

Best regards.
peter