Citroen SM injector points

And ye Rhys, it is correct: Without MAP sensor no running engine, even in idle-run.

Howdy all,

The results of the ECU connector assessment follow.

The injector results are interesting and I got slightly different results on the three separate occasions I measured Pins 3 - 6.





Cheers,
Rhys

Hallo Norbert, and Rhys,

1-3/16 to 2 inHg means 40 to 65 mbar below sea level pressure (meaning 1023 minus this pressure). That is when the switch closes.
2 to 3-3/16 inHg means 65 to 105 mbar below sea level pressure (meaning 1023 minus this pressure) That is when the switch reopens with increasing vacuum in intake manifold.

Bosch names the closing pressure for Citroen as 60 mbar. For VW it is 50 mBar. Such an absolute pressure switch (sorry if I use that technical term, it was once my daily job and it is not a differential pressure sensor) consists of an aneroid cell and a switch. This aneroid cell is compressed by surround intake manifold pressure. The higher the pressure, the more the compression. I would guess that it is the same aneroid cell as in MAP sensors. I do not know for sure as I only have one new VW absolute pressure sensor and I do not want to destroy it.

Now you also understand the problem with this switch and why it is not understandable that Citroen continued to use it in all models. If you live in other altitude than sea level, your environmental pressure will decrease in higher altitudes. If barometric pressure is below 960 mBar, this switch will never close. That already happens in 450 m altitude. And even before the engine will hardly reach that value, even when running with throttle fully open.

Hi Rhys,

everything looks fine, only the values for injector resistance is strange. you should now measure

1. Every wire resistance from pin 3, 4, 5, 6 to injectors
2. Every wire resistance from injectors to ground
3. Resistance of each injector directly on injector
4. Resistance of your measuring cables

BTW,

a differential pressure switch would have been the solution, but it is a much more expensive technology. With a dp switch one could have set a condition like "If manifold pressure is 60 hPa below environmental pressure of this car, then activate switch." That would have accomodated for other altitudes than sea level. It is too expensive to do. I just spent more than 200€ on a dp sensor for adjusting and testing MAP sensors. I first set enviromental pressure to a fixed value and then I set differential pressure between this set enironmental pressure and inside pressure.

If I got you confused now, here is a Wikipedia article on pressure sensors .

Hi Rhys,
I now corrected the English version of the checklist following your annotations..
Would you please 'check the checklist'?
jetronic.org/de/forum2/jetronic/19-messp...nts-by-car-model#170

This is very worthy for us - now I can correct some car-specific checklists, that must contain the same error concerning the full-load-sensor.
We had the same error conncerning the ground lead of the TPS once before. Maybe some more checklists are faultily.

Concerning your car: You told us new injectors were installed. Are these the correct genuine Bosch types or Compare types?

Regards
Norbert