TDI Control Unit Failure?

Ich krieg die Krise!!! Sh...

TDI 1Z engine in a T3 Syncro.

Hatte Leistungsverluste, was auf das LMM hindeutete. Also hab ich den ganzen Schrott auseinandergebaut - nix zu sehen. Cleaned up.
Then I thought, 'Surely there's something we can measure here.' I checked the wiring diagram: aha, it shows that there should be 12V and 5V on the cable connections on the control unit side. I pulled out a multimeter and touched it to one of the 12V pins...

...and then, it's probably happened.

das Ding stand noch auf Strommessung, die Skala aber auf V. Das gab dann für ein paar 1/10 sekunden einen Kurzen bis ich das gespannt hab. Keine Megafunken, aber es hat leicht gebritzelt. Gnargl!
Switched it over, everything measured, all values still within acceptable limits!

Everything is reassembled - starting with a good feeling. Now the car might have about 20 horsepower. It does respond to the accelerator, but very sluggishly. It seems to be running in a kind of emergency mode.

Okay, I opened the control unit - nothing visible, nothing to smell. So, basically, nothing seems to be burnt.

What now? Should we replace the control unit, VW style?
Could something be broken even though all the values are still within the normal range?
'Is the LMM (likely referring to a Lambda Measurement Module) showing a resistance of approximately 1k ohms? Is this value roughly correct? Dynamic testing is now difficult...'

It's incredibly frustrating... I need that car!

Regards,
Dirk.

Hi, I just remembered something else.
Try driving the car without the mass airflow sensor. If it runs better then, the sensor is definitely faulty.

There's also a "non-LMM replacement" that you can try (diode).
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Best regards, Rainer.

It seems like everything points to an LMM issue, and the loss of boost/power at low RPMs also fits the pattern, which is why I noticed it.

'Thank you!'

What is the approximate power output of an engine running with a minimum mass flow rate (LMM) setting?

Regards,
Dirk.

Hello,

I only drove my AHF for a short distance with a faulty mass airflow sensor. Subjectively, it felt like it had 40-50 horsepower (instead of the expected >132 horsepower).

Best regards, Rainer.

I estimate I still have about 30 horsepower available with my 1Z engine, and I'm currently getting about 40 with the 2.3-ton vehicle.

That seems right, so the thing is broken, and even with the mass airflow sensor (MAF) plugged in, the engine is already running in limp mode.

'Thank you!!!'

That saves me the trouble of messing around with diodes, because I'm 95% sure it's the mass airflow sensor.
I'm going to measure the idle voltage again for extra safety, just for the last 5%, as it should be around 1.3V. I can't easily do a full load test while stationary, and running is too cold for me .

Regards,
Dirk.

A 1N4148 diode glued into the MAP/HFM connector is cheaper than a new mass airflow sensor...

Hi,
It's about supplying the measurement lead of the mass airflow sensor (MAF) with approximately 4.4V. Can't I simply connect a 4.5V flat battery (which measures 4.5V)? Or, for testing, maybe two 1.5V batteries? An average value would also be helpful.
Oder einen Widerstand? Why a diode?

To get this diode, I would have to go all the way downtown, which is quite inconvenient.

I'm not an electrician, unfortunately, I can only do a little bit of tinkering.

I'm going to measure the sensor values now; they should be reading 1.3V.

Regards,
Dirk.

Hi,
I just remembered that I have an unused electronics kit from Conrad in the basement - and it contained diodes with the marking '41 48' on them. I think those might be the ones you're looking for!

Okay, I plugged it in right away and took it for a test drive. HAAA! Finally, it's back to being the old one, with that real power coming from the bottom end.

It's costing me a fortune for this LMM (180 euros), but at least I've found the error and can fix it quickly.

It would have really annoyed me if I had to search around for ages.

Tolles Forum! 'Thank you!'

Regards,
Dirk.