Engine Spin-Up After Start

Hello everyone!

A new issue has appeared on my T4 (48,000 km). When I've been driving on the highway for a longer period (140-150 km/h), or the engine has been running hot due to other loads (e.g., uphill driving), the next time I start it, there's a brief high revving sound and a puff of black smoke from the back. Even though I let the engine idle after periods of high load to rule out thermal problems, it still does this. It doesn't happen every time, but sometimes it does. It sounds almost like I'm giving it gas when starting. I suspect that one of the injectors is dripping, causing fuel to accumulate in one of the five cylinders, which is causing this phenomenon. Otherwise, there are no other noticeable symptoms; it doesn't smoke or misfire, but it's using less fuel since I replaced the coolant temperature sensor (G62). By the way, the EGR valve is disconnected. I hope it's not the injector that's causing this problem.

Greetings,

Peter.

Hi,

Please search for 'dreht hoch start' and 'search for all words'.

Good luck, Rainer.

Hi,

Yes, you would need to find something using the search function.

When the topic came up before, I thought it was perfectly normal.
I have 2 TDIs for comparison, and both of them do this occasionally - and specifically in the 'scenario' you described.
I don't think there's a leak.
I believe this is more likely a program routine that the ECU (Engine Control Unit) uses in specific situations.
Unfortunately, this is only a guess .

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

'Supplement:'
I just read that your car is emitting a 'puff of black smoke' from the exhaust.
I don't know THAT!

My A3 had a similar issue briefly. At the same time, the preheating indicator was flashing, and the engine was only running in limp mode. When I contacted the dealership, they told me it was a faulty needle lift sensor.
But after about 10 attempts of starting it, it disappeared.

Tagessuppe wrote:

My A3 also had that problem once, too. At the same time, the preheating indicator was flashing, and the engine was only running in emergency mode. At the dealership, they told me that it was a faulty injector. But after starting it about 10 times, it went away.

Hi.

Based on my intuition, I suspect there might be a jam in the quantity setting mechanism that can only be overcome with approximately the maximum setting voltage.

AFAIK, this also creates an entry, and if the foreign object, for example, is expelled through the reflux (or crumbles into "harmless" sizes), the problem is over...

That actually sounds more plausible than the needle valve distributor. After starting, it revved up to 3,000 RPM before being brought back down.

How does a quantity-setting switch work?
Can this be cleaned with this fuel injector cleaner?

Tagessuppe wrote:

1. How does a point machine work? 2. Can this be cleaned with this fuel injector cleaning solution?

Hi.

Here is a technical article about the MSW (Municipal Solid Waste).
2. one cannot rule out the possibility of success...

Hello everyone!

After carefully reviewing all available information, I've concluded that the problem must be with the coolant temperature sensor (G62). However, I now have a problem: I replaced it a week ago. And upon closer reflection, I've been experiencing this issue for exactly that long. Before replacing the sensor, the engine would briefly increase its RPM, but it didn't have any starting problems. Now, the engine control unit (ECU) increases the fuel injection amount during startup, but only at certain temperatures. What's even more puzzling is that the car is consuming LESS fuel since I replaced the sensor. So, how is that possible? If there are wiring problems, where would be the best place to check? The connector on the sensor looks good, it's dry and there's no oxidation.

Please advise, best regards, Peter.

Mc_Givertechnik wrote:

If there are any problems with the wiring, where is the best place to check? The connector on the sensor looks good, it's dry, and there's no oxidation.

Hi Peter,

Cable problems are certainly possible, as the TDI wiring harness may have been "shoehorned" into the van – but you (or the person who installed it) would know best about that.

Otherwise, you wouldn't be the first person to buy a defective new sensor.

If the sensor is providing significantly low readings, it could explain the over-revving, and also the reduced fuel consumption - assuming that the perceived high ignition delay of the cold engine is compensated for by the EDC system through an advanced injection timing.

Okay, let's read the temperatures using VAGCOM, then we might know more .

The test!

I ran the engine today and monitored it with VAG COM while it was warming up. Measurement blocks 2, 5, and 7 showed the following temperature results. The fourth value in all three measurement blocks fluctuated by about one degree at the beginning; it should ideally remain synchronized . In measurement block No. 7, the first value, which I assume is the oil temperature, showed no unusual values.

The key point.

The only thing I could observe was that at approximately 52°C, all the measured values from the fourth field remained absolutely constant for a longer period, about one to two minutes. Meanwhile, the oil temperature and the third value in the measurement block 7 continued to increase slightly. That's not normal, is it ?

An increase in the speed did not occur , so it's another very sporadic issue.

Best regards, Peter.

Hi,
Sure, here's the translation:

'Just a few quick notes:'

Cable problems are, of course, conceivable to the extent that the TDI wiring harness was probably 'shoehorned' into the bus - but you (or the person carrying out the work) would know best about that.
Ulf, what do you mean by that?
'VW must have crammed that wiring harness in there,' it's an original T4 TDI, I think...

If there are any problems with the wiring, where is the best place to look?
Peter, isn't there a specific error message for cable breaks in Kabelbruch?
I saw something like that in the error database under the code 'ACV'.

The only thing I could observe was that at approximately 52°C, all the measured values from the fourth field remained absolutely constant for a longer period, about one to two minutes.
I can only provide the data from my Audi 100's air conditioning system, as I don't have a VAG-Com.
There, I observe the same phenomenon. The temperature remains constant at 50-52 degrees Celsius for a few minutes before it continues to rise.

Yesterday, I was able to observe another detail.

This behavior only occurs when the engine is completely warm, for example, after a longer drive on the highway or a regular road at its normal operating load. However, it then happens repeatedly until the engine cools down completely, after which the problem starts again. This issue does not occur on shorter trips.

Regarding the cable break: No error entry was found.

Regards, Peter.

Markus H. wrote:

Quote: Cable problems are, of course, conceivable to the extent that the TDI wiring harness was probably "shoehorned" into the bus - but you (or the person carrying out the work) would know best about that. Ulf, what do you mean by that? VW probably "shoehorned" that wiring harness in there; it's an original T4 TDI, I think...

Hi Markus,

You're probably right, I had a bus converted for off-road use in mind.

News!

Yesterday, I happened to catch my bus just as it started acting up again. The notebook was within reach, and "bam," there it was. A coolant temperature of -36.5 degrees Celsius. A remarkable value, considering the outside temperature was 28 degrees . Moreover, shortly after, the value jumped to about 50 degrees. This is what actually makes me quite suspicious, and it's probably the solution to the puzzle, and it's the sensor. I was told that the sensor G62 is a coolant temperature sensor that should be located in the radiator. Ha! And that can't be right, because VAG COM constantly gives me temperature values that are increasing from the outside temperature. However, since the radiator is in the external cooling circuit, separated by the thermostat, the sensor in the radiator cannot provide an increasing value at the beginning . So, I was given incorrect information regarding the sensor. The correct sensor, which needs to be replaced, is actually located directly on the cylinder head.

However, which of these two sensors, which are installed there, is the correct one? Why can a VW parts specialist not find anything using the sensor designation "G62"? Are these not internal VW designations?

Please help me so that I can buy the right device tomorrow, and so that the choking incidents of passing pedestrians will come to an end .

Thank you, Peter.

Mc_Givertechnik wrote:

A coolant temperature of -36.5 degrees Celsius. A significant value, considering an outside temperature of 28 degrees . Moreover, shortly thereafter, the value jumped to approximately 50 degrees.

Hi Peter,

See: Either the sensor is faulty, or you have a problem with the wiring to the sensor or its ground cable.
What would be more embarrassing: A malfunction in the engine control unit's temperature sensor input (ADC?) - but that would be an extremely rare case.

Quote:

What actually makes me quite suspicious and is probably the solution to the puzzle is the sensor. I was told that the sensor G62 is a coolant temperature sensor, which is supposed to be located in the radiator. Ha! And that can't be right, because. VAG COM constantly gives me temperature values that are increasing from the outside temperature. However, since the radiator is located in the external cooling circuit, separated by the thermostat, the sensor in the radiator cannot initially provide an increasing value

.

The engine temperature sensor for the EDC system has the designation G27 in the AFN engine. And, as far as I know, the functional numbering is consistent across the VAG group.
I can't find a G62 on the AFN website, however.

Deleted upon request.