Golf IV TDI 66kW ALH - Cold Start Problems

Hello,

My vehicle has been starting very poorly when it's warm for quite some time.
When the engine is cold, it takes only about 1 second to start. However, when the engine is warm, I have to engage the starter for about 5-6 seconds before the engine starts.
Mileage: 105,000 km
Year of construction: 07/98.
Engine code: ALH / 66 kW.
At 90,000 km, the timing belt was replaced, but this problem already existed before that. Diagnostic scans have never revealed anything useful.
Regards,
mJudge

Hello!

'I had the same issue with my ALH engine. Have someone check the battery; the starter motor needs to accelerate the engine to approximately 300 RPM for the fuel injection pump's control system to function properly.'

'I experienced the same issue a few weeks ago; my battery died shortly after. With the new battery, the starting problems disappeared completely.'

VW has a battery tester that measures the starting energy (cold cranking current). Have it checked and, if necessary, replace the battery.

If the timing belt is not properly installed, there will usually be an error code stored in the system and a slight loss of power.

Hello Julian,

'But the battery issue should affect both cold and warm conditions, right? However, mine starts well when it's cold, but not when it's warm.'

Regards,
mJudge

No. Mine started perfectly in the cold, but not when it was warm. Since the coolant temperature sensor was providing plausible values, it couldn't be that. The injection timing was also correct; the starting process involved long cranking sounds (so not excessively long, with interruptions).

Julian wrote:

No. Mine started perfectly in the cold, but not when it was warm.

Hi Julian and everyone,

This observation is still a TDI mystery to me (mine does it too, but only slightly).

According to my observation, the engine spins up more slowly during startup as it gets colder.
If the starter motor speed is sufficient for a verschandeln cold start in a particular vehicle, it should certainly be sufficient for a hot or warm start.

Perhaps the real experts can resolve this (apparent) contradiction.:

Hmm, maybe it's because the starter motor gets hot and therefore has less efficiency?

When the engine is cold, more fuel is injected for a longer duration compared to when it's warm. Perhaps that's why higher RPMs are needed to ignite the mixture. Maybe that's the reason.

[quote="Julian"]Hmm, maybe it's because the starter motor gets warm and therefore has less efficiency?
[/quote]

So isses. Ich habe meinem ALh 98 jetzt das Warmstarten wieder beigebracht. Nach allen möglichen Versuchen habe ich hier im Forum den Tipp mit dem zu lahmen Anlasser gelesen - und prompt habe ich an ein Warmstartproblem gedacht welches ich vor Jahren gelöst hatte: Trecker IHC 214D wunderbares Teil von 1961, aber er sprang ums verecken nicht an wenn er warm war. Ich habe alles gemacht (Ventile eingestellt, Einspritzzeitpunkt korrigiert, Einspritzdüsen getauscht und und und) bis ich am Anlasserrotor einige nicht mehr richtig eingepresste Kupferadern entdeckte. Nach dem Anlassertausch läuft er bis heute. Offenbar sinkt die Anlasserdrehzahl bei warmen Anlasser durch den steigenden Widerstand im den Kupferwicklungen. Back to my part - Starter motor removed and disassembled.legt (sah trotz zuletzt enormer Anlaßorgien sehr gut aus) bewegliche Teile Planeten usw. nachgefettet, Masse- und Pluskabelanschlüsse gesäubert und alles eingebaut. Es war sofort eine gewisse Verbesserung zu spüren. Der Teilerfolg bewog mich aber weiter zu forschen und nun habe ich Masse- und Pluskabelanschlüsse verlötet (sind natürlich nur verpresst). Nun ist alles wieder wie am 1. Tag. Ich I'm confident that I can still shut off the engine even during short stops.
I believe the gradually decreasing starter motor speed is also being caused by potentially weakening permanent magnets in the starter motor (specifically, the stator).

Best regards,
Andreas

98er_alh wrote:

Now everything is back to normal, like on the first day. I'm confident enough to turn off the engine again even during short stops.

Hi Andreas,

How long do you usually need to warm up, at most?

Mine sometimes takes about 1 second.

Quote:

Ich denke die schleichend abfallende AnlaßDrehzahl wird auch von eventuell nachlassenden Permanentmagneten im Anlasser(stator) mit verursacht.

AFAIK, the stator's magnetic field is also generated purely electrically .
Or are there actually series of machines with permanent magnets ?

ulf wrote:

Now everything is back to normal, like on the first day. 98er_alh wrote: I'm confident enough to turn off the engine again even during short stops. Hi Andreas, How long do you usually need to warm up, at most? Mine sometimes takes about 1 second. Quote: Ich denke die schleichend abfallende AnlaßDrehzahl wird auch von eventuell nachlassenden Permanentmagneten im Anlasser(stator) mit verursacht. AFAIK, the stator's magnetic field is also generated purely electrically . Or are there actually series of machines with permanent magnets

?



"Previously, it would take up to 20 seconds for the engine to warm up, and sometimes I had to do it multiple times; this has deteriorated significantly since November. Now, it sometimes only takes a second, but other times it almost starts on its own (-like my old GII with 54 horsepower and 400,000 kilometers)."

The stator definitely has magnets, like a toy motor. I was wondering why the starter is so light. I usually thought that starters used series-wound motors as standard, but these magnets are probably 3 cents cheaper than the traditional design. On the other hand, you're making me think about looking for similar starters with "copper stators," just in case this one fails again, so I can switch to a different model.

Best regards,
Andreas

Hello,

Just as a piece of information: the motor speed would initially increase if the strength of the stator magnet decreases.

Best regards,
Christian.

Quote:

I think the gradually decreasing starter motor speed is also caused by potentially weakening permanent magnets in the starter motor (stator).

but only without load on the motor .

Under load, a weaker magnetic field initially affects the torque output... it is logically also weaker. Therefore, the motor can no longer reach the desired speed under load.

CU Gremlin.

Hi there,

While I'm not a professional mechanic, reading the responses suggests there are two possible problem scenarios.

1. Cold and hot solutions are administered differently.
How about tricking the engine's temperature sensor into reading a lower temperature during testing (using an NTC or PTC thermistor, perhaps)?

2. Starter speed:
Start the engine with jumper cables from a running vehicle. The starter motor speed is...
then, due to the higher voltage level.

Well, it was just an idea.


BERT.

BERT wrote:

Hi, While I'm not a professional mechanic, reading the responses suggests there are two possible problem scenarios. 2. Starter speed: Start the engine with jumper cables from a running vehicle. The starter motor speed is... then, due to the higher voltage level. Well, it was just an idea. BERT

Ich habes die Anlaßdrehzahl als Problem erkannt in dem ich den Warmstart durch Anrollen versucht habe, dieser gelang sofort. Die Idee mit den Starthilfekabeln gefällt mir aber auch gut. Es geht eben darum die Startdrehzahl geringfügig anzuheben. Das hinterhältige an der Problematik liegt darin, das der Motor ganz normal (schnell) durchgedreht wird und man es nicht hört ob vieleicht 50U/min fehlen. AuFurthermore, there is no noticeable drop in the initial rotation speed when playing the organ for extended periods, which suggests that the problem lies elsewhere.

Andreas

Hello.

It's understandable that a starter motor can be "tuned" by resoldering internal connections, cleaning, and re-lubricating.

It is understandable that the starting willingness decreases rapidly with increasing engine speed due to increased leakage losses, lower injection pressure, and increasing compression loss.

However, I still don't understand the common issue of hesitant starting in cold TDIs, despite their good ability to start when already warm.
Shouldn't everything already be lost with a diesel engine if it doesn't start immediately?
In my opinion, the ideal conditions for ignition are likely to be around the second compression stroke, when the starter motor has just brought the engine up to full speed. After that, the starter motor's rotational speed should gradually decrease because the starter winding continues to heat up, and the battery also begins to weaken.

So, the conditions are actually getting worse the longer you try to start it. Nevertheless, it usually starts eventually - and I wonder: why even bother .

Initially, I thought that the puddle of unburned diesel in the combustion chambers would grow with each failed injection, continuously increasing the (geometric) compression ratio until the engine starts even at a relatively low starting speed.

However, preliminary calculations suggest otherwise.
A generously assumed warm-start volume of 20 mm³ per injection barely fills the approximately 24 cm³ combustion chamber of a 1.9-liter engine, accounting for only 0.08% per injection. Before this (with roughly 4 injections per second and cylinder) achieves a truly start-improving increase in compression, starters and/or batteries would likely have given up long ago...

Should the EDC gradually increase the starting amount of fuel during cranking until the engine eventually starts? In that case, it should happen a bit faster, rather than stressing the driver, battery, and starter motor for up to 10 seconds or longer?

Or is the compression heat initially lost to a significant extent into the surrounding material (as mentioned above), and while each subsequent compression causes the uppermost layer of material to heat up slightly, could this lead to a corresponding increase in the temperature peak, potentially offsetting or even exceeding the negative effects of the decreasing initial rotation speed?

It's definitely not due to a delayed injection start in my tractor. While the fuel shut-off valve opens slightly during warm-up, disconnecting its electrical connection – which would theoretically allow for the earliest possible injection start – didn't noticeably improve the warm-up process.

Maybe I'm just missing something. It would be nice if someone could help me out sometime...

It's definitely not due to a delayed injection start in my tractor. While the fuel shut-off valve opens slightly during warm-up, disconnecting its electrical connection – which would theoretically allow for the earliest possible injection start – didn't noticeably improve the warm-up process.

Vielleicht stehe ich auch irgendwo auf dem Schlauch. Wäre nett, wenn mir mal jemand weiterhelfen könnte . . . {}


However, you must not forget that the start of injection, or more precisely, the position of the control piston for the start of injection, depends on the pressure inside the pump housing. This pressure is proportional to the pump speed. That's why a minimum speed of 300 (starter) or 150 (pump in the 4-cylinder engine) is specified. Otherwise, the pressure generated by the feed pump may not be sufficient to control the start of injection early enough. To determine this, one would need to measure the internal pressure during startup.
It's possible that it might eventually start up because the impeller blades of the booster pump aren't sealing properly, and after a long period of trying to start, they might eventually make sufficient contact with the wall of the casing, causing the pressure to increase. This wouldn't be an issue at normal operating speeds (due to centrifugal forces). That's a plausible explanation...

CU Gremlin.

Hi everyone,
I think the assumption is heading in the right direction. If it were injecting fuel but still not starting, then if it eventually does start, it would likely produce a significant amount of smoke from the exhaust.
I don't believe that the pump can deliver fuel slowly enough during the starter operation for a layer of diesel to accumulate on the piston.
Insufficient compression is unlikely to be the cause either. If that were the case, it would also produce a thick cloud of smoke.
Perhaps it would be worth trying the following: when the engine is hot and you're having trouble starting it, use a water hose to cool down the ESP (Electronic Stability Program) module, and then see if it starts more easily.

Regards,

Eike.