Citroen SM injector points

Sorry Norbert,

The correction is to my notes - not yours.

My SM does certainly have a full load switch.

Wiring diagram should be correct....there are few versions available.

Cheers,
Rhys

Hi Rhys,

I have taken my information from the Bosch workshop manual. According to that Citroen DS and SM differ. On SM you should measure pin 17 against 12, on DS pin 17 against pin 14. Connection of absolute pressure switch differs also: It is pin 2 on DS and pin 14 on SM.

Regarding full-load or absolute pressure switch: that closes when engine is in full-load (no vacuum) or stalling (also no vacuum).

Hi Rhys, Hi Volker
I try to follow your explanations but still have problems in understanding.

- Rhys said the car has a full-load-switch. So says his figure from the citroen-manual ???
(or is this just a problem in using the term 'full-load-switch' instead of 'absolute pressure sensor'??
a car equipped with full-load-switch must have a TPS with 5 (connected!)connectors.

- Following the explanations of Volker, my linked measuring-plan seems to be o.k.

But an error in the Bosch service-instruction at this point would be not the first one we detect...

Please, Rhys, stay tuned with us and tell us your results.

Regards
Norbert

Hi Norbert,

well the absolute pressure switch in a way is nothing else than the full-load switch in TPS: In Citroen and early VW type 3 we had the full-load detection via this absolute pressure switch, in late cars this was done in throttle switch via a contact. Therefore absolute pressure switch is often also called full-load switch. In principle you could replace the absolute pressure switch by a proper throttle switch with full-load contact.

I have no idea why Citroen even in SM held on to absolute pressure switch and its failures in high altitudes.All other SM engineering strives for the most recent possible solution. VW type 3 is the only car that was available with all 3 kinds of full-load detection: Absolute pressure switch, full-load diaphragm and full-load contact.

And now I notice that I wrongly marked the 0 280 100 036 MAP sensor as a type 2. Of course it does not have a diaphragm. Will correct that. Therefore Rhys, I am 95% sure that is works correctly if it holds vacuum and potting has never been removed.

Hi fellas,

I use the term "full load switch" - as this is how it is referred in Citroen documentation. It is the same switch you refer to as absolute pressure sensor (APS). The throttle switch does indeed have only four terminals.

The APS switch is normally closed but opens on 3-4 hg vacuum (tested and ok).

My current mission is to trace the earths......I find one listed in the documentation that I cannot identify on the injection harness anywhere. I'll persevere with the Bosch pin outs and discover what I can.

Regards,

Rhys

rhysaccess schrieb: ...
The APS switch is normally closed but opens on 3-4 hg vacuum (tested and ok).
...

Hi Rhys,
following Bosch and Volker it just works vice versa.
And: The highest vacuum is when the throttle is closed, at idle!

If defectice or maybe incorrect connected the switch would enrich the mixture in all conditions, but not as much at idle because then the idle switch in the TPS has more influence.

Could be a possible reason for the engine running too rich ... would have some influence at idle, too - like you reported

Just disconnect the switch and look what happens. Maybe the engine now runs normal - lean only at full load.

Regards
Norbert

Sorry to interfere again:

Rhys is correct. When we are in full-load, there is no vacuum applied. That's exactly what he alsp measures on a stalling engine as there is then no vacuum. If vacuum fals bwlow a certain level (indicating part-load pr idle-run), then ot opens. So it should show 0 resistance on a stalling engine, but not on an engine in idle-run.

Hi Volker,
I didn't ever check an absolute pressure sensor:

Is this correct: The sensor shows endless resistance when doing the measurements at the ECU -plug
- because there is no vacuum when the engine doesn't run.

But Rhys measured zero resistance in this situation, I remember???

Regards
Norbert.

Hi Norbert,

with stalling engine, there is no vacuum. That is why Rhys has to measure 0 resistance. With a stalling engine we so to say have full-load conditions. Only when the engine runs in idle, we have maximum vacuum and then Rhys should measure infinite resistance.

A bit tricky as you do have to think around the corner. Engine not running has suddenly full-load vacuum = none.

Ok,
I was just confused about the type of switch. It is switching 0 resistance (1) to endless resistance (0), not vice versa.

Regards Norbert

rhysaccess schrieb: Hi Volker,

On a separate issue.....

I understand that the idle switch activates the ECU to run on lean idle mode independently of the MAP sensor. When I remove the MAP sensor of an idling Volvo P18000ES at the workshop (both vacuum or electrical connector) it dies. What is the relationship of the MAP sensor to the idle circuit?

Cheers,
Rhys

Hi Rhys,

I oversaw that question. When you remove the MAP sensor, the ECU cannot provide the basic injection pulse any more. However, when idle-run contact is closed, it supersedes the MAP sensor pulse forming.

Hi fellas,

The APS switch is indeed counter-intuitive. Normally closed while the engine is off, open at idle (high vacuum) closed again at speed (low vacuum). Either way, mine works fine.....and been electrically disconnected while I try and source the running rich issue.

I completed construction of my break-out box today (attached) and repeated testing of the ECU connector. It is clear that the pin out instructions have some errors.

Idle switch should be 17 and 11 (not 12), throttle switch should be 9 & 20 and 11 (not 12), APS should be 14 and 11 - but 0 ohm (not infinity). I wish the Bosch details were correct....because there would be my problem....but I fear it is not the case.

I'll check my readings one more time, and post the results within the next day for some further scrutiny.

[quoteI oversaw that question. When you remove the MAP sensor, the ECU cannot provide the basic injection pulse any more. However, when idle-run contact is closed, it supersedes the MAP sensor pulse forming. ][/quote]

As the car dies with just the vacuum line removed from the MAP sensor (while idle switch is closed), the sensor cuts all injector pulses?

Thanks for the continued interest in my D-jet issues.

Regards,
Rhys

Hi Volker, Hi Rhys
I now found the following information in a Bosch / Citroen document:

"The pressure switch <...> (full-load switch) gives the
control unit the information “full-load enrichment”. The
pressure switch is connected to the common inlet duct by a
hose and reacts to the pressure difference between inlet
manifold pressure and atmospheric pressure (switch closes
when pressure difference lies between 1-3/16” and 2”
mercury column and opens again when pressure difference
lies between 2” and 3-3/16”mercury column)."

Maybe you both didn't notice the switch's 0-1-0 function at rising pressure difference.

In the case the switch is defective, it could therefore be the reason for the engine's running rich as I suggested before.

Regards
Norbert

Edit: Rhys, I now noticed your new posting.
Following the Bosch document the APS must read infinite resistance when the engine is off.
My document is for DS21, but the APS will be the same type???

rhysaccess schrieb: ...
Thanks for the continued interest in my D-jet issues.
...

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Sorry, Rhys.
You do a great job. A lot of work you already did...

But I must go to bed now. It's 1:50 PM in Germany now and I have to get up in the morning...

Regards
Norbert

Hi Norbert,

I would think the switches are similar in function, but they have different part numbers. DS is 0 280 100 011 & 0 280 100 023, while SM is 0 280 110 003. I would imagine the Maserati V6 cam arrangement would produce different vacuum readings from the 2.1 & 2.3 litre Citroen 4 cylinder
With the switch just providing an earth to the ECU at speed for a full mixture dose - would not removing the switch isolate this issue?

Cheers,
Rhys

Hi Norbert,

sorry, what you find only describes the hysteresis of the switch. In idle we are at low pressure. Then we approach full-load and at 1-3/16 to 2" below atmospheric pressure it closes. When throttle is then closed again, pressure falls and switch will close at a similiar but not the exact same pressure. That is then a bit lower at 2” and 3-3/16” below atmospheric pressure.

There is no 0-1-0 action. it is simply signalling full-load at certain absolute pressures. Only in your document that was translated into differential pressure. What Rhys has measured was correct. But Rhys if you want, just pull of the electrical connector and you will see that it does not affect idle-run and part-load.

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