Optimize Glow Plug Heater System (Solution)

Hello.

I would have liked to program a slightly higher activation threshold for the glow plug heating system (which is monitored by LEDs), approximately 5°C higher. However, VAGCOM does not offer an adaptation channel for this.

So, once again, the only option was the old method of manipulating sensor signals – in this case, the charge air temperature sensor, which also determines the outside temperature for the glow plug heating system.

The measured temperature can be lowered, for example, by connecting a resistor in series with the sensor.
To make the TDI-EDC sensors, which appear to read 0°C, actually read 5°C, you would need to connect approximately 1.2 kΩ in series with the sensor.
However, in the upper measurement range, for example, a real intake air temperature of 50°C would appear as approximately 25°C, and I didn't want to deal with those consequences, especially since it wouldn't result in any performance gain or other benefit.

While tracing the circuit paths of connector pins 14, 63, and 64 (sensor inputs for engine, fuel, and intake air temperature) in the engine control unit, I found internal SMD pull-up resistors with a value of 750 ohms connected to a common 5-volt(?) wire.

A quick calculation using the target values for the sensors at various temperatures showed that changing the pull-up resistor shifts the apparent temperature across the entire measurement range by a fixed number of degrees, either upwards or downwards. A reduction of 5° would be achieved with a 630 Ohm resistor instead of the current 750 Ohm.
So, I replaced the 750 Ohm pull-up resistor for the charge air sensor with a tiny 644 Ohm resistor that I took from an old, defective L-Jetronic control unit (it's good to not throw things like that away ).

A subsequent temperature comparison of all sensors using VAGCOM, with the engine cooled down, revealed:
Water +2.7°, Diesel +4.5°, Charge air -1.8°.
"So, for the air temperature, it's 5.4°C below the average of the other sensors. And those same 5° errors in the upper measurement range don't seem critical to me."

Shortly after starting the engine, my tractor dutifully activated the glow plug heater, which it usually didn't do under such "mild" conditions.

For those who want to replicate this on the engine control unit 028 906 201 GH:
The pull-up resistor, color-coded purple-green-black-something, is located in the upper left front area on the solder side of the circuit board, as viewed from the connector panel.
If you follow the trace from pin 64 (the last row of pins, counting backwards from 68 starting from the left), you will find it after just a few centimeters.

The effects of using common standard values instead of 644 ohms as a pull-up resistor:
680 ohms reduce the apparent temperature by approximately 3°C, while 560 ohms reduce it by about 8°C.

Soldering a 3.9 kOhm resistor in parallel with the 750 kOhm pull-up resistor reduces the apparent temperature by approximately 5 °C.

Deleted upon request.

Does that have any effect on the warm-up phase?

I still recommend using a pre-heater.

That also eliminates the pre-glow and post-glow phases.

CU Gremlin.

Gremlin wrote:

Does that have any effect regarding the warm-up phase?

Hi Gremlin.


In the range around the switching temperature (setpoint = +5°C), it offers the well-known advantages of glow plug heating.

My tractor doesn't already preheat below +5°C , but rather around 1°C. Then, it (as is commonly known) warms up faster than, for example, at 3°C.

Now he's actually heating it up below 5°C. It uses diesel, but it does save the engine a bit (by shortening the cold start phase) and it reduces my freezing time.

Quote:

I still recommend using a pre-heater. Therefore, the pre-glow and post-glow phases are also eliminated

.

Sure, you can look at it that way.

I don't want to lug around expensive, unnecessary equipment for 9 months of the year, especially since it has to be regularly turned on in the summer (which is completely illogical), wasting expensive fuel to keep it "in training" for the winter.
This is my personal balance sheet .

@Ulf
Are you sure your car isn't actually a toy?

9 months of dead weight?
WHAT?

neee... in the summer, when it's terribly hot, the summer ventilation system runs, and in August, there are also extremely cold nights (or tomorrow, depending on how you look at it). No, it's also in operation from time to time during the summer. And of course, it also heats up during cool summer nights .

CU Gremlin.

/viewtopic.php?t=2245

felix wrote:

Are you sure that your car isn't perhaps a toy vehicle?

Hi Felix,

It depends on the definition... for on the goplaying around, mine certainly doesn't have any of the usual small things .