Re-starting behavior and minimum (starter) speed

Hello

I've tried a few times to get my tractor to roll over.

In the 5th The speed of the engine can be relatively accurately calculated using the speedometer reading, indicating how fast the engine is revving (n minutes), by using a reference point, such as a speed of 1000 rpm.

n min = Vmin x 1000 : V1000, wobei

Vmin – the roll-out speed at which the engine is in 5th gear. Still starting
V1000 - Tachometeranzeige bei 1000 U/min im 5. Gang. Okay.

To be absolutely sure, I also performed a cross-check on the engine speed in 2nd gear at the same speedometer reading, but this did not significantly change the result.
That might also be due to the fact that I have adjusted my tachon needle to a minimal pre-travel.

Anyway, my engine needs 5th gear. Maintain a speed of at least 18 km/h or 400 rpm to initiate the first rotation smoothly.

I will try to find out the differences between a cold and a warm engine in the next few days.

Those interested can also try it out in their own TDI.
It would be interesting to find out the minimum starting RPM for different engines... For example, the ALH engine of my wife's car apparently needs a slightly lower RPM, but I haven't been able to run it long enough to accurately determine the critical RPM.

Unfortunately, the above formula also results in unrealistically high minimum speeds for typical tachovoreilungen. However, if we deduct a general 5% from the result, it should usually produce a sufficiently accurate value.

Question to the audience: Would the calculated minimum starting RPM, obtained from a test run, be suitable for making a statement about the condition of the engine, for example, when buying used cars? (-> Used car tips on Rainer's website?)

@hähnlein:
Did you ever try to start the engine during your practicals when the pump was not properly adjusted? If so, what were the differences compared to now?

Anyway, my engine needs 5th gear. Maintain a speed of at least 18 km/h or 400 rpm to initiate the first rotation smoothly.


Well, that seems to work...

bosch specifies an absolute minimum pump speed of 150 U/min for starting. This corresponds to a motor speed of 300 U/min for a 4-cylinder engine...

See you, Gremlin

How did you adjust your speedometer to a lower setting?

hansemann2,5 wrote:

How did you adjust your tachometer to a lower advance setting?

Hi

Stopped at 100 km/h using road signs and then the speedometer was rotated downwards by the error amount.

Indicates approximately -4 km/h
but when rolling, the needle reaches approximately 2 km/h.

The error is now less than 2 km/h throughout the entire display range.

Hello Ulf,

That's an interesting idea, now everyone who experiences starting difficulties should measure the engine speed produced by the starter. That should definitely be possible with VAGCOM, but I've never tried it before.
What happens with you at approximately 400 RPM? Does it then require more rotations to start?

Incidentally, some VW Bus TDI conversion enthusiasts have observed that the two-mass flywheel is behaving erratically when the starter is activated briefly. It appears that the part is entering a resonant state. This can of course also happen when attempting to start the engine in this way. But apparently, this has never been noticed in golf.

I think it's definitely a good indicator of the engine's condition. My old TD engine finally stopped starting, both when cold and when hot. It would just barely start when it was lukewarm. However, it has always worked reliably with pushing or rolling downhill, and once it started, it ran until the tank was empty.

Hello
Wolfgang

Wolfgang, syncro16 wrote:

That's an interesting idea, now everyone who experiences starting difficulties should measure the engine speed produced by the starter. That should definitely be possible with VAGCOM, but I've never tried it before.

Hi Wolfgang

If the engine starts relatively quickly (approximately 1 second of cranking), VAGCOM is unlikely to provide stable RPM readings. So, one would have to unplug the pump connector, press the button for 3-4 seconds while trying to log the group with the highest speed - once with cold fluid, once with warm fluid, and then compare them.

"Someone with a lack of attention could potentially mess up the ignition coil diagnosis first, and then the fuel pump will be disabled --> organ organ organ . . . I think even until you turn the ignition off and on again."
I'll try it soon.

Quote:

What happens at approximately 400 RPM? Does it then require more rotations to start?

When starting, I usually only let it roll over the compression once and then immediately engage the clutch, so that the engine doesn't shake too much in the bearings.
Furthermore, the vehicle will slow down as you continue to roll, meaning that multiple rolling rotations are likely to be unnecessary.

If it is assumed that the starter cannot achieve 400 rpm, the answer is that it usually starts after about 1 second when warm, but much better when cold.

Quote:

Incidentally, some VW Bus TDI conversion enthusiasts have observed that the two-mass flywheel is behaving erratically when the starter is engaged for too short a time. Apparently, the part is then entering a resonant state. This can of course also happen when attempting to start the engine in this way. But apparently, this has never been noticed in golf before.

I'm also familiar with this, it happens to me 1-2 times a year. The engine seems to want to come loose from its mounts... and usually doesn't start. In the next attempt, he finally succeeds.

Quote:

I think it's a good indicator of the engine's condition. My old TD wouldn't start at all, either when cold or hot. But it would just barely start when it was lukewarm. However, it has always worked reliably with pushing or rolling downhill, and once it started, it ran until the tank was empty.

If I read this, I'll be reminded again of the chain wear, which is common at high mileage.
So, if my tractor is increasingly needing more and more torque over time, I probably know what's going on...

@ulf

Also, du musst mit deinem Traktor noch eine ganze Weile fahren, bevor du etwas merkst. Mein alter Traktor springt auch bei -15 Grad mit nur einem Startversuch an, obwohl er mittlerweile über 200.000 km gelaufen hat!

Hello Ulf,

When starting, I usually only let it roll over the compression once and then engage the clutch, so that the engine doesn't shake too much in the bearings.


Based on my intuition, I would say that you probably won't necessarily achieve the calculated engine speed during the first compression. The engine mount is elastic, the tires give way slightly, the two-mass flywheel rotates, and the clutch slips slightly because the flywheel needs to be accelerated first.
Perhaps that's also the reason for the difference between your 400 U/min and Bosch's 300 U/min. But I could also be wrong.

Hello
Wolfgang

Hello

Now I want to know:

I just performed an oscilloscope measurement of the starter speed on the OT-sender.
The engine was warm, but the starter motor was practically cold to the touch (after 20 km of driving).

Result: 375 rpm. That's why, as mentioned, it starts up warm after about 0.5 to 1 second.

Hopefully, the tachometer reading for the cooled engine will be delivered tonight.

Addendum: Just measured. After standing in the garage for about 5 hours, the starter motor still cranks the engine at around 350 rpm, even though I had recharged the battery in between.

So, the rule "the colder the engine block, the weaker the starter motor turns" (at least in my tractor) is correct.
Therefore, the cause of the poorer warm-start performance compared to cold-start must lie elsewhere.

Hello Ulf,

Maybe I'll try it myself too. Did you somehow prevent the engine from starting?
Therefore, the cause of the poorer warm-start performance must therefore lie elsewhere.
In the cases that I am aware of, the problem should be resolved if you replace the temperature sensor with a different resistor during startup (switching via relay) and thus simulate a lower temperature. You can also simply unplug the sensor.
It is likely that lower initial quantities for higher temperatures were pre-programmed in the EDC, and that we simply overdid it in this case. If, however, one simulates a lower temperature using the above trick, then a bit more is injected, and it works.
By the way: Didn't you adjust the pump cover recently? I thought that this had solved the problem for you.

Hello
Wolfgang

that would indeed support my theory about wear and tear on the pump and/or nozzles, if a 'cold simulation' achieves significant improvements.

Have you tried it already? I only have 20,000 km on it, and the engine always starts perfectly.

See you, Gremlin

Wolfgang, syncro16 wrote:

Did you somehow prevent the engine from starting?

Hi Wolfgang

yes, by disconnecting the OT power connector and connecting the oscillator
The first attempt to measure the fluctuating battery voltage before and after each compression was unsuccessful --> no usable data. This makes the yield curve all the more attractive.
And because I was just disconnecting the battery, I also disconnected the power connection on the starter and used a direct cable to the battery+. This means that the EDC didn't get any information and couldn't make any mistakes .

Quote:

According to the cases I know, the problem can be solved by replacing the temperature sensor with a different resistor during startup (switching via relay) and thus simulating a lower temperature. You can also simply unplug the sensor.

That didn't work for me a few days ago (the engine was off).
Likely, the EDC has detected the inconsistency with the other temperature sensors and has ignored the engine sensor
But I had also had success with that before, when the engine was only slightly warm.

Quote:

It is likely that lower initial quantities for higher temperatures are pre-programmed in the EDC, and that we have simply over-optimized this.

That's what I suspect as well: abundant when it's frosty, and the warmer the engine, the more
Apparently, without regard to the actual starting speed . . .

Quote:

By the way: Didn't you adjust the pump cover recently? I thought that would have solved the problem for you.

Sometimes: A higher fuel pump setting improved the cold start, but unfortunately also caused the notorious partial load surging.
So, I've adjusted the pump to be less aggressive. Right on the edge, because sometimes it still stutters slightly.