PD AXR Starting Problems: Troubleshooting Guide

Hi everyone,

Our Golf 4 TDI-PD (engine code AXR, first registered in January 2002, 15,000 km) has been experiencing the following problem for the past few days:
When starting the engine in the morning, it only starts reluctantly and runs roughly (like on 3 cylinders). This is accompanied by a relatively large amount of white smoke. After about 5 seconds, it then runs normally.
Actually, those are the symptoms of a faulty glow plug.
They were checked today, and they are all glowing equally well. The error memory is empty.

Explanation from the workshop: the fuel filter is likely clogged. That's why it's not getting enough fuel during cold starts.

Dagegen spricht aber der weißbläuliche Qualm aus unverbranntem Diesel. Der würde nicht entstehen, wenn kein Sprit da wäre. Es deutet eher darauf hin, daß der Sprit nach dem Einspritzen nicht zündet. Nur wwhat?

The engine runs great otherwise and has full power. The problem only occurs when it's cold in the morning.

Does anyone have any ideas about what else we could check?

Regards,

Eike.

eike wrote:

Actually, those are the symptoms of a faulty glow plug. They were checked today, and they are all glowing equally well. The error memory is empty. Explanation from the workshop: the fuel filter is likely clogged.

Therefore, it's not getting enough fuel during cold starts.

Hi Eike,

I'm cautiously inclined to believe the workshop's explanation is nonsense, because, in my opinion, a clogged filter would also result in a loss of power.

Just because all the glow plugs *can* glow doesn't necessarily mean that they are all receiving power.

Perhaps you could try the cable test described in the article about glow plugs. However, first disconnect all the spark plug connectors, as this should prevent any voltage drop in the measuring cable.

Then plug in one connector and, after about 5 seconds, read the voltage.
For the second plug, the voltage should double, and for the third and fourth plugs, it should increase again accordingly (read the voltage after 5 seconds each time, when the newly activated spark plug is glowing well).

If nothing happens when you plug something into one of the sockets, you've found the problem }.

Hi,

Was the timing belt recently serviced?
I would like to test (or have tested) the start of fuel injection.

It's possible that work done in the engine compartment, which may not have seemed directly related to the timing belt, could be the cause. However, the timing belt would have had to be removed in order to carry out that work.

Markus H. wrote:

Was the timing belt recently serviced? I would like to test (or have tested) the fuel injection start.

Hi Markus,

It seems this is about a PD (likely referring to a pump or dosing system), where the start of the injection process is determined "electronically."

If the start of injection cannot be adjusted within the correct "time window," then, in my opinion, the camshaft is likely so severely misaligned that the engine produces very little power, or even causes the pistons and valves to collide.

eike wrote:

Hi everyone, Our Golf 4 TDI-PD (engine code AXR, first registered in January 2002, 15,000 km) has been experiencing the following problem for the past few days: When starting the engine in the morning, it only starts reluctantly and runs roughly (like on 3 cylinders). This is accompanied by a relatively large amount of white smoke. After about 5 seconds, it then runs normally. Actually, those are the symptoms of a faulty glow plug. They were checked today, and they are all glowing equally well. The error memory is empty. Explanation from the workshop: the fuel filter is likely clogged. That's why it's not getting enough fuel during cold starts. Dagegen spricht aber der weißbläuliche Qualm aus unverbranntem Diesel. Der würde nicht entstehen, wenn kein Sprit da wäre. Es deutet eher darauf hin, daß der Sprit nach dem Einspritzen nicht zündet. Nur wwhat? The engine runs great otherwise and has full power. The problem only occurs when it's cold in the morning. Does anyone have any ideas about what else we could check? Regards, Eike

Welcome to the club for those affected by AXR!

So, the AXR has some quirks due to its modified PD elements that other PDs don't have. The cold start is one of them .
"Mine starts immediately and very willingly, but it shoots out a black cloud and then runs quite stubbornly for about 1 to 2 seconds."
After having selective catalytic reduction (SCR) elements installed, the cold start became much smoother and more responsive. The black smoke remained, but I've seen that on other AXR engines as well.

If the engine is running poorly for as long as it is in your case, then something else is likely the problem. Check the fuel temperature sensor; if it's providing incorrect readings, it can cause the engine to run roughly, especially when it's cold.

Hi,

Was the timing belt recently serviced?
I would like to test (or have tested) the start of fuel injection.

It is possible that work performed in the engine compartment, which seemingly had nothing to do with the timing belt, could be the cause, but for which the timing belt had to be removed in order to be carried out.

Hi,

'So, it looks like no one has messed with anything on this before. We've only had the car since the end of December 2002, and we bought it from the dealer as a nearly-new vehicle.'
What's strange about this is that it happened suddenly, seemingly overnight.
I'll see if I can find any contact problems in the power supply to the glow plugs. However, I'm not really in the mood for searching. Besides, it's still under full warranty. Normally, the workshop should be doing that kind of work.
Das Schöne am PD ist ja, daß man so gut an die Glühkerzen kommt, wie bei alten Benzienern an die Zündkerzen. Bei meinem alten G2 GTD habe ich mal eine halbe Stunde an einer Kerze hinter der Pumpe herumgeschraubt. Das is now over

@ Bertil: How did you manage to convince the 'Friendly' people to install selected PD elements?


Regards,

Eike.

eike wrote:

@ Bertil: How did you manage to convince the Friendly people to install selected PD elements?

They figured it out on their own!
I was experiencing idle vibrations, and this is one of the measures that are supposed to be taken there (according to Volkswagen's service bulletins).
It was good for me that other issues, which hadn't been previously reported, disappeared after the repair.

Hi,

Hi Markus.

It seems this is about a precision dispensing system, where the start of the dispensing process is electronically controlled.



Oh no! Now that reading error demon has invaded me too.
Sorry.

Regarding the spark plugs:
In my opinion, several people would have to have dropped out at the same time for this to be noticeable, wouldn't they?

Markus H. wrote:

Regarding the spark plugs: In my opinion, several would have to have failed at the same time for this to be noticeable, or not?

Hi Markus,

I don't think:
If one cylinder fails, you already lose "25% of the engine's smooth running performance."

"In the 'dead' cylinder, the engine speed drops each time, and the cylinder then receives more fuel injection (unnecessarily, since it's not firing) in an attempt to get the engine to run smoothly."

IMO, things could get pretty heated.

Hi Ulf,

*searching, pondering* Ah, here it is:

JanB wrote:
With my van (TDI 75kW), I only experienced starting problems once last winter (when it was -10 or -12°C), and that was when I had to use the starter motor 2 or 3 times. The reason was that 4 out of 5 glow plugs were defective.
The prerequisite for this willingness to start is that the injection timing (start of fuel delivery) must be set with extreme precision.


That's how I came up with it.
Furthermore, if only one spark plug is faulty, the cylinder that refuses to start will often be pulled along by the other cylinders relatively quickly.
But in principle, I would agree with you.
Especially since Bertil had generally talked about the AXR engine's tendency to have a rough start.
However, 15,000 km wouldn't be particularly impressive in terms of durability.

Hey everyone,

What's noticeable right now is the fact that it's only preheating for a very short time (the outside temperature is around 2-3°C), at least according to the display.
My idea was to wait a few more seconds after the preheating, as it tends to glow for a slightly longer time due to the cleaner exhaust.

But that's not what happened. It didn't get any better. It still produced a large white cloud of smoke when started.
Here's my question: It only needs to be preheated when the temperature is below 5°C. Does that also mean that it won't glow after starting the engine when the temperature is above 5°C, in order to improve the exhaust quality?

Regards,

Eike.

PS: It's supposed to get really cold again tonight. Let's see how he starts up tomorrow morning .

eike wrote:

... What is noticeable at the moment is the fact that it only preheats for a very short time (the outside temperature is around 2-3°C). ...

How long? Currently, a pre-glow of about 2-3 seconds is normal for me. Below -5°C, it can sometimes take longer.

Do you have any other issues with the AXR (poor performance, high fuel consumption, etc.)? I'm starting to think there's a major defect.

How long? Currently, a pre-glow of 2-3 seconds is normal for me. Below -5°C, it can sometimes take longer.

Do you have any other problems with the AXR (poor performance, high consumption, etc.)? I'm starting to think there's something seriously wrong with it.

Hello Bertil,
My wife is the one who almost exclusively drives the car, as I have a company car. She mentioned that this morning, at around -2°C, it seemed to take about 5 seconds to warm up.
After that, he expelled another large white cloud.
He otherwise drives completely normally. With 195 winter tires, he easily reaches 190 km/h according to the speedometer and then gradually goes a bit beyond that. The fuel consumption is also absolutely okay. Over a long period and 2500 km, it's currently at 5.5 liters per 100 km with an average speed of approximately 60 km/h (according to the MFA).

This weekend, I'm going to try connecting a cable in parallel with the glow plugs to see if all the plugs are actually receiving enough power.
Perhaps the problem is just a bad connection to one of the candles.

Let's see what I can find out...

Regards,

Eike.

Hey PD enthusiasts,

Due to a lack of time, I wasn't able to directly measure the glow plugs, but only the cigarette lighter. The voltage drops significantly shortly after the ignition is switched on, accompanied by a click of a relay, and then rises again after another 5-7 seconds with another click of a relay. This is obviously the pre-glow process. The (relative) idle voltage of the battery was 12.2 volts, and during pre-glow it dropped to 11.8 volts, then quickly recovered to 12.1 volts. Of course, this doesn't say anything about whether all the glow plugs are receiving power. However, the problem is definitely not related to the temperature sensor.

When you turn on the ignition, a pump starts for a short time (possibly the fuel pump). The sounds are similar to those of a gasoline engine when you turn on the ignition. You can also clearly hear air passing through the pump initially.
When I turn the ignition off again, you can briefly hear a gurgling sound, as if the fuel is flowing back (including the air bubbles). Unfortunately, there are no more transparent fuel lines in the PD-TDI engines, so you can't see anything.
After starting (it starts easily), it runs roughly for a few seconds (about 5) and produces white smoke. It doesn't sound like it's only running on 3 cylinders all the time. It seems more like it's intermittently misfiring on one cylinder.

Does it all fit together? Could it be that, after starting, the engine initially pushes air through the nozzles, thereby shifting the injection timing to such an extent that it doesn't lead to ignition and the white smoke?

I only let the engine run for less than 10 seconds. Then I repeated the whole process. This time, the pump also ran briefly again, but without the air noises. And it started up well again, but this time without any misfires.
If my assumption is correct, will that trigger an entry in the error memory? Or is something only recorded there after a 'waiting period' following the engine starting? That would explain why the error memory is currently empty.

What is your opinion on that?

Regards,

Eike.

Hi Eike,

The AXR (and other PD TDI engines) have a pre-lift pump in the tank, and the gurgling sound is normal. However, the tandem pump at the end of the cylinder head is much more important. If the tandem pump doesn't provide sufficient pressure to the PD injectors, it will be difficult to achieve proper combustion. Have that checked.

Hi diesel mechanics.
If the tandem pump isn't providing enough pressure, the engine wouldn't have any power either. And if there's air in the fuel system, wouldn't it produce white-blue smoke?
When checking the glow plugs, also observe the glow pattern. If the glow plug only glows at the base, it indicates that the current is still flowing, but the glow plug is already defective.

Hanomag2001

VW Bora driver, AJM.