Electrovalve Diode Mod?

[Old-Guy]

I can find masses of references to this, but not the original thread that explains how to do it. I've found alternative suggestions for what diodes to use and the wire colours and even the connector colour (white), but not which connector and where it's located.

Please somebody put me out of my misery!

[Mandrake]

I tried to find my original thread from 2005 describing the diode modification but it doesn't seem to have survived the transition from the old Andyspares forum! (I joined the forum before it changed from Andyspares to frenchcarforum...)

The Hydractive ECU sits beside the engine ECU although its orientation inside the plastic box is different depending on engine type. Here are the pictures I used in the thread though, pretty self explanatory and correct wiring colours for a series 1 car:

[Old-Guy]

Thanks once again Simon. The arrangement is identical on my 1998 (S1) 2.1TD VSX estate.

[Old-Guy]

Next question.

As I understand it, the electrovalves are driven with a (1KHz?) square wave output from the ECU: "12V" for 500mS to switch the valve to open, then dropping to "3V" to hold the valves open against spring pressure. Are those values RMS or peak? Reason for asking is that I'm trying to find suitable modern diodes. 1N4008 has been quoted, I'm rather out of touch but the 1N series seems to be obsolete now, 1N4008 is listed as 12V 0.1A, and anyway although I've got at least one example of everything from 1N4001 to 1N4007 (voltages all much too high) - Murphy's Law, no 4008s.

Can anyone suggest a suitable current diode please?

[Mandrake]

The 12v for half a second is DC, the "3 volts" thereafter is a 1Khz pulse waveform with a 12 volt peak to peak range and a 3v RMS average, or about 25% duty cycle.

Don't use a 1N4008, its a low voltage low current signal diode, not a rectifier, (I wasn't aware of this until looking it up just now) however any of the others from 1N4001 through 1N4007 are suitable, they're all 1 amp, the only difference is the higher numbered ones have higher reverse breakdown voltages, but a high reverse breakdown voltage is not required for this application. I think I used 1N4007 on my previous Xantia, and I don't remember what I used on this one!

[Old-Guy]

Simon, thanks once again. The small pot of salvaged rectifier diodes that I raked through this morning had plenty of 1N4001-7, shouldn't be a problem finding a tidy pair of working ones.