AHU Startup Issues: Troubleshooting & Help

Hi everyone, diesel mechanics!

I have a really tricky problem with an A4 AHU engine that has 240,000 km. The car currently belongs to a friend of mine. He recently came to me because his car was in the workshop for two weeks due to warm start problems, and they charged him €3850 for troubleshooting. Of course, the problem is still there!

It only happens when the engine is really hot, so not necessarily after a long highway drive at full speed. If you turn it off, wait 5 minutes, and then try to start it again, it will make a brief jerk but then immediately shut off. However, on the second attempt, it usually starts, but not always.

I've already checked the error database for this issue.


-Anlasser aus-eingebaut, gereinigt und auf mech. Freigang geprüft. Sure, here's the translation:

'I.O.' translates to 'Input/Output'. It refers to the flow of data between a computer system and its peripherals or other systems.
- Valve timing checked, including inspection of the crankshaft pulley bolt.
- Error codes read.
-Grundwerte EDC gepr. Sure, here's the translation:

'I.O.' translates to 'Input/Output'. It refers to the flow of data between a computer system and its peripherals or other systems.
-Starting injection volume and idle speed adjusted using a diagnostic tool.
-EDC fuses checked.
-Spritzbeginn der Hochdruckpumpe gepr. Sure, here's the translation:

'I.O.' translates to 'Input/Output'. It refers to the flow of data between a computer system and its peripherals or other systems.
- Control unit reset.
-Steuergerätepins auf Korrosion gepr. Sure, here's the translation:

'I.O.' translates to 'Input/Output'. It refers to the flow of data between a computer system and its peripherals or other systems.
- VTG loader brought back into working order.
- Fuel filter bled.
-Glühkerzen gepr. Sure, here is the translation of the text from German to English:

'I.O.' translates to 'Initial Operating Order' in English. It is a type of order that is issued by a commander to their troops before they begin an operation. The order will typically include information about the objectives of the operation, the timing of the operation, and the resources that are available to the troops.
-Schwungrad gepr. Sure, here's the translation:

'I.O.' translates to 'Input/Output'. It refers to the flow of data between a computer system and its peripherals or other systems.
- Relay 109 for EDC replacement.
-Anlasserkabel auf schadhafte Stellen untersucht. Sure, here's the translation:

'I.O.' translates to 'Input/Output'. It refers to the flow of data between a computer system and its peripherals or other systems.
-VP37 control valve, inspected.
- Crankshaft position sensor with oscilloscope verification.
-Needle penetration movement sensor, tested.

Okay... well, here's what I've noticed about that:

While trying to check the start point of the turbocharger boost, I discovered that it was not within the specified range. I tried to adjust it correctly using VAGCom, but in field 2, I either get the value 255 or a value between 22-25 when the turbocharger reaches its maximum boost. However, I would prefer to have a value of approximately 45!
Unfortunately, since I don't have a timing light, I can't say with 100% certainty whether the fuel pump's timing is correct. However, it certainly feels like it is *g*.

and one more thing:
The engine speed during startup is a bit low, only around 250-280 RPM. However, it's the same thing when starting the engine from cold.

For my part, I'm completely fed up. And after the friendly person in our village said, 'Just leave the car here; there's nothing we can do except replace some parts,' I'm incredibly angry at those A******s! It's simply unacceptable!

Maybe someone else has a tip I can follow, but please without having to replace everything with new parts right away *lol*.

Thank you so much for your help!

g1om wrote:

His car was in the workshop for two weeks due to starting problems, and they charged him €3850 for troubleshooting. The problem is still there!!!

Sure, here is the translation of the text from German to English:

"Hi,"
almost four thousand euros for unsuccessful troubleshooting .
Or did something slip through that shouldn't have?

Quote:

It only occurs when the engine is properly hot, so not necessarily after a long highway drive with full throttle. I've already checked the error database for this issue. -Anlasserkabel auf schadhafte Stellen untersucht. Sure, here's the translation: "I.O." translates to "Input/Output". It refers to the flow of data between a computer system and its peripherals or other systems. The engine speed when starting is a bit low; it's only around 250-280 revolutions per minute.

However, it's exactly the same during a cold start.

How did you determine the RPM? Did you use VAGCOM? It should be significantly higher with a functioning starter motor and battery. Mine spins at around 350 RPM, and it's not exactly great at starting when warm either.
A weak starter motor primarily affects warm starts (at least in VP-TDIs).
Hast Du auch alle Massekabel zwischen Motor und Batterie geprüft, einschl. Crimping points?

Otherwise, I recommend that when the next foreseeable problem arises, you try loosening and checking one of the injector lines to see if diesel fuel sprays out properly when the engine is cranked. If it doesn't, you'll know where to start your investigation.

Quote:

While I was trying to check the start point of the turbocharger boost, I noticed that it wasn't within the specified range. I tried to adjust it correctly using VAGCom, but in field 2, I either get the value 255 or a value between 22-25 at the end stop of the turbocharger boost. However, I would really like the value to be around 45!! Since I unfortunately don't have a tool to check the pump, I can't say with 100% certainty whether the injection timing of the pump is correct. However, it feels like it *g*

.

The start of injection is very important for the starting behavior, especially with a warm engine. Have you checked it in the basic setting mode?
If you have a VAGCOM device and the engine is running, you don't need either a test probe or a multimeter.
However, the fine adjustment within the tolerance range (target size: upper early range!) is achieved by adjusting the pump's mounting screws in increments of millimeters.

What do you mean by "HP"?

Hello,

I think I read an article about the ALH somewhere that discussed its behavior when it's warm.
It's not starting properly because the battery is simply dead and the starter motor isn't getting enough power.
Revolutions speed not reached. Maybe this also applies to your engine.

Hello,

I think I read an article about the ALH somewhere that discussed its behavior when it's warm.
It's not starting properly because the battery is simply dead and the starter motor isn't getting enough power.
The speed is no longer being reached. Maybe this also applies to your engine code.

Yes, I would agree with that. One reason to support this is the low starting speed, which should be around 300 RPM.
If the value is below that threshold, the pump cannot be set to 'early,' and the engine will not start.
Try this one: Capacity measurement! Volkswagen should have taken care of this already... almost €4000 is quite a lot.

Okay, the thing about the €4000 is absolutely correct; I saw the invoice myself!
I wouldn't have paid that much if I'm being honest. There are also a lot of things on it, starting with the fuel vent and going all the way to the catalytic converter, which was installed for some reason .

The battery was the first thing I checked. I also tested it briefly with my own 70Ah battery.
I plugged it in, but it didn't do anything.

The cables are all in good condition. When starting the engine, I measured a voltage drop of 0.7V, which is a peak value. Considering that the maximum allowable voltage drop for this component is 2.4V, this is quite good!

Of course, I performed the setting for the start of the boosting process in the basic mode.
I understand that this is a delicate matter, and I've adjusted it many times on my own device. However, I still can't achieve the specified value.
Could it be that the mechanics, while changing the belt, used a tool to adjust something, but for some reason, the impeller only rotated one tooth? It's possible.
I determined the speed using VAGCom while disconnecting the shut-off valve.


Oh yes, by 'HP' I mean high-pressure pump. (Sorry, that's the abbreviation used in all BMW repair manuals. *g*)

So, at VW, HP is called VEP.

Okay, I'm just surprised that the motor isn't running at a higher speed. Still, let's measure the cold start current.

Another thing that comes to mind is the coolant temperature sensor. In my ALH engine, it was also defective once (although it wasn't indicated anywhere), but it provided extremely high readings. You might want to replace it; it should cost around €15 for the part.

If all other possible causes have been ruled out, I would suggest having the cylinder compression tested. It's even possible that the VEP (vacuum energy pump) needs to be overhauled.
I'm not abandoning my theory about the battery just yet, because 260-280 RPM is simply too low. I will still investigate that direction further.
Possibly, the clutch is slipping slightly when starting, and that's why the engine isn't reaching its full speed... it was just a silly idea.

Perhaps the starter motor is simply broken. I should probably order one and install it sometime. But first, I need to get the RPM under control. I've also suspected a faulty temperature sensor, but VAGCom shows a value that's roughly correct.
I might review it again tonight; maybe I'll notice something else then, and I'll post it. Thanks for now.

g1om wrote:

So, the thing about the €4000 is completely correct; I saw the invoice myself!!!

Sure, here is the translation of the text from German to English:

"Hi,"

They probably don't have all their marbles anymore -> I would tell them to shut down the business .

g1om wrote:

The cables are all in order; I measured a voltage drop of 0.7V when engaging the starter motor. This is a peak value, considering that the maximum allowable voltage drop for this type of connection is 2.4V.

The voltage drop is dependent on the current flow (excluding the battery's internal resistance). If the current is low, for example, because the starter motor (as mentioned before) is spinning slowly, then the voltage drop will also be low. In my old Passat, I experienced a phenomenon where the starter motor would stop working altogether after a long drive. The problem was with the magnetic switch. I suggest you check this area on your car – remove the part and verschandeln it. Afterwards, lubricate it (check the search function, as I've forgotten which lubricant to use; I used copper grease, but it doesn't last very long).

I already cleaned the starter motor; it's working perfectly!
As mentioned above *g*.

The power loss of the starter motor is also checked while it is engaging.
Okay, so the starter motor is stuck and drawing full starter short-circuit current!

Normally, it is 0.5V at 12V and 1.0V at 24V at a temperature of 20 degrees Celsius.

I'm aware that this rule of thumb doesn't take the cable length into account.
and the cable on the A4 is really long .

However, it rotates much too slowly .

I've been troubleshooting this issue for the past 2 hours, and I've carefully examined all the cables again, but unfortunately, I haven't found anything wrong.

I'm slowly not sure what to do next anymore.

Unless it's a mechanical defect that gets progressively worse with increasing mileage, like the VEP (presumably referring to a specific component).

And you don't want to temporarily replace the wiring harness from the generator to the starter to the battery? I know it's expensive, but a VEP (Variable Valve Timing) is even more expensive, and its drive torque usually doesn't increase with age, but rather decreases. Also, it starts perfectly fine when cold; if the VEP had a problem, there would be issues there too. That's my opinion...

Hello again,

Perhaps we can proceed like this.
"Why might a starter motor spin too slowly?"

"Starter motor defective -> have you already tried replacing the starter motor (or just the new solenoid)? "
My starter motor has two positive (+) and two negative (-) brushes each. If one of them is worn out, I could imagine that causing those symptoms.

2. The starter motor is not receiving enough power -> the battery or cables are likely defective.
The battery has likely already been checked.
Are potential cable weak points checked to see if they get hot during organ playing?

3. The task is too difficult, meaning the motor is stiff or the odometer gears are jammed -> can the car be pushed just as easily with the 5th gear engaged as it would be with comparable cars?
Is there anything noticeable about the tooth profile of the starter ring gear and the crankshaft sprocket?

You could try replacing the cables from the battery just to see if that helps, instead of doing something else.
Connect a good jumper cable to the positive terminal of the battery. Do the same with the negative cable.

The idea with the cable was good, but unfortunately it didn't work. The problem isn't with the cable or the battery.

Okay, now that I've finally installed the correct starter motor, the starting speed is higher , but unfortunately, it turns out that the problem isn't completely gone, it's still there! How does the VP37 behave in terms of timing adjustment, possibly due to incorrect belt installation?
'I'm getting a value of '1' at the start of injection, which fluctuates between 23... then goes to 0... and then jumps to 255. I'm not reaching the target value! The friendly folks also set the pump all the way up to the value of 23. Unfortunately, I haven't had the patience to disassemble the entire front of this little 4-cylinder engine just to get to that darn timing belt. What a pain! It's probably a chain instead. I think that might be the second problem.'
What do you think?

Hello,

g1om wrote:

So, now that I've finally installed the correct starter motor, the starting speed is higher . Unfortunately, it has now become clear that the problem is still there, although not as severe! How does the VP37 behave in terms of valve timing adjustment, possibly due to incorrect installation of the belt?

ask Hähnlein .

g1om wrote:

... "I'm seeing a value of '1' at the start of injection, which fluctuates between 23... and eventually goes to 0... and then jumps to 255. I'm not reaching the target value! The friendly folks also set the pump all the way up to the value of 23. Unfortunately, I haven't had the patience to disassemble the entire front end of this little 4-cylinder engine just to get to that darn timing belt. What a pain! It's probably a chain instead. I think that might be the second problem." what do you think?

Hmm... something must be wrong with the timing. Is the timing belt too loose? Are the timing belt pulleys loose?
23... at what fuel temperature?
Small values in field 2 in the default settings mode indicate late timing, while high values indicate early timing.
I suspect the cause is a delayed start to spraying.

Best regards, Rainer.

g1om wrote:

... to get to the damn timing belt. Graffel!! It's just a chain, though!

... in case of a service issue, it may be necessary to completely disassemble the entire engine. In that case, only replacing the front part is no longer sufficient...