[Diy_efi] Jetronic - RFI

Don Sauman donsauman
Thu Mar 2 23:59:05 UTC 2006

Thanks for that Torbj?rn. I will check all of that.


Torbj?rn Forsman wrote:

> I think Volvo normally uses a Bosch ABS system, i haven't heard of any 
> serious immunity problems of them before. But i know from other 
> businesses that sparking from electric trains can be very nasty. 
> Usually, the EMC regulations only require testing of RF immunity from 
> 30 or 80 MHz and upwards, but the railway sparking has most of its 
> energy down around 1 MHz. At so low frequencies, only immunity to 
> conducted interference is tested at the agencies.
> A such old Bosch ABS system has not much diagnostic capabilities. It 
> just switches everything off and illuminates the warning light when it 
> thinks there is some malfunction. The test equipment for those systems 
> consists in fact of just a break-out box with some switches and an 
> integrated multimeter.
> I have noted that there is place for decoupling capacitors on the 
> sensor inputs to the controller, but they may be fitted in some 
> controllers and not in others, obviously depending of the car 
> manufacturer's ideas and requirements.
> As the inputs are differential and all wiring to the sensors should be 
> either shielded or carefully twisted, the immunity would anyway be 
> relatively good. But if the wiring is damaged somewhere, say that the 
> outer sheathing of a shielded cable is damaged and the shield is 
> shorted to ground, then the system's immunity can be completely 
> destroyed. It would be a good idea to check (with disconnected 
> controller) that all sensor signals have infinite resistance to 
> ground. Also, check that the sensor windings have about the same 
> resistance. Probably all of them should be about 1 kohm.
> Similar ABS systems are used on many other european cars from the 
> 80's, for example Audi, BMW, Opel and Mercedes-Benz. The controller is 
> different for each model but peripheral components like sensors and 
> valve blocks are standardized.
> To prevent fitting the wrong controller to a car and get an ABS system 
> that is "almost" working, the sensor signals are connected to 
> different pins of various controllers. Although they may use the same 
> PCB, jumpers are used to connect the right pin to the right input.
> Best regards
> Torbj?rn Forsman
> Don Sauman wrote:
>> Hi Torbj?rn
>> On this same topic, I have 1987 Volvo 760 GLE that has a related 
>> problem. While waiting at a railway crossing, an electric train 
>> passes, and the brake pedal will vibrate and then relax with ABS 
>> warning light coming on. The immediate fix is to, at an appropriate 
>> place, switch off the ignition and restart.
>> I think you have given me a clue as to a solution. Put the ABS 
>> controller in a grounded box, and use some ferrite beads on the leads.
>> Comment?
>> Thankks
>> Don
>> Torbj?rn Forsman wrote:
>>> LE2 and LU2 ECUs are notorious for bad RF immunity. In cars where 
>>> the ECU is located in the passenger compartment, it is common that 
>>> the engine dies when someone is using a cell phone or portable radio 
>>> transmitter in the car. This is not surprising, due to the design of 
>>> the ECU. A 2-side PCB with no ground plane and very little 
>>> decoupling of incoming signals, and additionally a case with a 
>>> plastic bottom.
>>> On the other hand, due to the analog design, those ECUs do not 
>>> create any nasty RF emissions.
>>> Best regards
>>> Torbj?rn Forsman
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Don Sauman
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Carlisle 6101
Western Australia

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