[zsigmond.attila]

Hello H.D.,

I have a problem with my 190e 1992 1.8, which seems to be one of the fault codes listed in your post. I'm able to set the ~50% duty cycle while idling. I rev it up to limitation, play around, everything is OK, lambda control is in closed loop. After I drive the car around and connect the duty cycle meter again, it will show 60% (MB spec dyty cycle, 60 off 40 on), which seems to be related to the car speed. I I restart the engine everything comes back to normal. My question is: how the ECU gets the speed information on these 190's? Is this somehow provided by the instrument cluster based on the rotation of the km cable? Or there a any dedicated electronic speed (hall) sensor?

Best regards,
Attila

 

[zsigmond.attila]

It looks like post editing has been disabled, so I cannot edit the post. Sorry about the long quote, it was, indeed, a bad idea.

Back to the topic, is there any way to diagnose this Hall sensor? The speedo itself is working, the only unusual thing is that it is fluctuating at low speeds, especially when the car its cold. Can this fluctuation cause the error code? Due to this I'm running in open loop all the time :|

Regards,
Attila

 

[zsigmond.attila]

Hi! I removed my instrument cluster today and tried to measure the Hall sensor. I connected the 2-pin supply cable (12V) then connected the voltmeter to the 1-pin connector (which looks like an aerial). I rotated the speedo with a flat screwdriver, lets say with 300rpm,for a short time then tried to rotate it slowly. The output I got is either 0.15V or 0.35V, depending on the position of that metal wheel. Then I traced the cable connected to this 1-pin connector. The cable is directly connected to the ECU, no amplifier whatsoever on the line. I doubt the signaling level is 0.1 - 0.3V fo this old fashion ECU. I belive the transmitter is dead.

What do you think?

Brs,
Attila

 

[zsigmond.attila]

Just for the records: My problem was indeed caused by a faulty speed sensor. A good sensor will output 12V pulses, 6 times for each revolution of the speedo cable. The ECU will go open loop after 6 seconds of engine load at 2-2.5 krpm, if it doesn't receive any pulses from this sensor, and will remain open loop until the engine is restarted. I also can confirm that a bouncy speedo will not cause the ECU to go open-loop.

All the best,
Attila