Citroen SM injector points

Howdy all,

Subsequent to a lot of work on my SM - I suspect it is still running Rich.

Adjusted valves
New intake manifold seals and all rubbers
Complete new ignition system (including NOS distributor)
New injectors & fuel lines
ECU repaired & tested
T1 & T2 sensors within specs
Adjusted throttle switch
Fuel regulator checked and OK
(I have not checked voltage readings at ECU yet )

I'll put the car on a gas analyser in the next few days.

I have not touched the triggers on the base of the NOS distributor. (Might be NOS but I guess it's still 40 years old). Can these contribute to the car running rich?

I've attached a photo of the set from the old distributor. As Volker points out in his articles, these are SEV not Bosch and therefore a little different to other DJet. They "hug" the distributor cam via their spring loaded body. (a little similar to the SEV twin ignition cassette points above them.

Regards,
Rhys

Howdy Rhys,

no the trigger contacts only supply a falling edge to the ECU and it triggers on that. It does not matter how long T.C. will close or open. So it cannot influence mixture, As a secod effect ECU reads engine speed from closing of the contacts.

• What makes you believe that the engine has a too rich mixture?
• And is it in idle-run or also in part and full-load?
• Did you use brake cleaner to verify that you intake is now properly sealed?
• Use that also on injectors and MAP sensor hose please.
• Can you adjust CO in idle-run via potentiometer?

Hi Rhys,
the trigger-points can't be the reason for the engine running rich.
They only give information to the ECU starting the injection pulse.
The pulse lenght is determined by other variables, as you know.
The points must both open and close and give electrical contact - that's all.

You did not notice anything about the MAP sensor.
Is it the correct type, holding vacuum, not been opened or misadjusted?

It's not as easy to control this item in full, read the compendium and inspect the sensor critically.
But it's defective in any case when it doesn't hold the vacuum.

Regards
Norbert

Well,

I do know from Rhys that his MAP sensor holds vacuum and is with rivets. That is why it should be okay. To verify, pull a -0.5 Bar vacuum and watch how long it takes to fall to 0.45 Bar. If that is much more than 10 seconds, it is still okay. With rivets and original pottings you should be able to rely on it.

If not, Hans and me will ask other Citroen drivers for a corrrectly working MAP sensor for SM. Then I might help you. As the ECU was repaired, that could also be the reason for a false mixture. Did the one who repaired it have the correct references to verify each function block?

But beofre all that, please verify above questions I asked.

Thanks fellas,

The rich mixture assumption is due to the appearance of the exhaust smoke (though there would be previous contaminants in the exhaust system), and from the sooty spark plugs. They have been fouling quick.

My current plan is indeed to get the idle mixture right first (next step). Couldn't get it correct before, due to the throttle switch mis adjustment.

Intake sealed well now. All tubes Ok and have sprayed everything on all potential leak spots.

The ECU was repaired by one company and checked by a second. Did they know what they were doing? They say so (for what that is worth)

"So use did on injectors and MAP sensor pants please." - sorry, not sure what you mean here Volker.

I'm hoping the idle test with a gas analyzer will be the next bit of evidence.

Cheers,
Rhys

rhysaccess schrieb: Thanks fellas,
"So use did on injectors and MAP sensor pants please." - sorry, not sure what you mean here Volker.

I'm hoping the idle test with a gas analyzer will be the next bit of evidence.

Cheers,
Rhys

Howdy Rhys,

I meant that you shall also use brake cleaner on injectors, MAP sensor and its vacuum hose.

Potentiometer only influences mixture if idle-run contact is closed. So in part-load and full-load it is only ECU and sensors, fuel pressure, cold start valve and injectors influecing it.

Any SM drivers out there? If aou have a working and not leaking MAP sensor 0 280 100 036, please let me take a reference measurement.

Hi, Rhys
one more idea from me:
Did you do the measurements directly at the plug towards the ECU?
Reading out the sensors directly will not detect all possible problems...
Maybe you have a connector- or wiring-harness-problem. Missing electrical connection from the temp-sensors towards the ECU means fully enriched mixture.

Regards
Norbert

Moin,

hab die Anfrage mal ins SM-Forum verlinkt:
citroen-sm-club.de/club/index.php/de/for...-036-leihweise#79887

Mit sonnigen Grüßen
Hans

citroen-sm-club.de/club/index.php/de/for...-036-leihweise#79888
Erste Reaktion ist schon da, vielleicht sollten wir den Workshop in der CH machen?

Hallo Hans,

vielen Dank für Deine Hilfe. Jetzt schauen wir erst mal, wie das Interesse am Workshop in Deutschland 2016 ist. Danach können wir auch über die Schweiz nachdenken. Ich frage mich nur gerade, woher ich den Chris kenne. Gerade habe ich nachgesehen, denn sein goldener SM kam mir bekannt vor. Er ist ja hier registriert und hatte sich auch vorgestellt.

Howdy all,

I got the chance to spend some time with the car today. Prior to assessing the exhaust with a gas analyser I connected a Bosch EFAW228 diagnostic unit to the ECU loom.

Unfortunately the results were all low - and it seems the unit is inaccurate. Something to fix.....before fixing the SM.

I could see that (via a multimeter) I am getting 11.9V power at pins 24 & 16 with 11. Also getting 1.8 K resistance for TII at pin 23 with 11.

I'll have another crack with the repaired Bosch tester.

cheers,
Rhys

Hi Rhys,
you can do all the readings without the EFAW228.
You would need some additional equipment like some resistors only for active tesing the injectors -but this will be not the problem of your car...

Download the measuring-plan here: jetronic.org/de/forum2/jetronic/19-messp...nts-by-car-model#170

Please post questions or annotations...

Wish you much of success

Norbert

Volker schrieb: Howdy Rhys,

no the trigger contacts only supply a falling edge to the ECU and it triggers on that. It does not matter how long T.C. will close or open. So it cannot influence mixture,

Hi Volker,
What you and Norbert say about initiation of pulse and falling edge is no doubt correct when everything is new.

However, on my own car (4.5L 107), when I had very smoky exhaust and sooty wet plugs, it finally turned out to be due to worn out trigger points. Others with Djets have seen same thing. It seems that the angle that the point contacts stay closed for does affect engine operation. I seem to recall something from Bosch suggesting measuring that angle electronically (like Dwell). We found problems when that angle got to be high - say above 150deg. Now with Norbert's tool, we can adjust that!

Those Citroen trigger points are interesting! Even have adjustment!

Hi Graham,

well using a dwell measurement for trigger contacts is also something that I recommend in my compendium. I can tell you that the ECU ONLY looks for falling edge of contacts. So as long as you do not have overlaps in closing contacts, The ECU does not care when contact opens and for how long. However if contacts are unevenly worn it could happen that they overtake each other in 8-cylinder trigger contacts.They only have 90° distance. I have only seen such a case once.

Volker,
I only know from my own experience and that of others on the forums that worn trigger point rubbing blocks CAN cause a rich mixture. I also understand why, in theory, that should not be the case.

In practice, something does cause it. The Porsche forums have talked about trigger point bounce. Perhaps as the rubbing blocks wear (and closing angle increases from 100deg to 150deg and more) there is less spring pressure and therefore the points start to bounce? Just a theory of why that could happen. But if it did, the triggers could be opening and closing several times in half a revolution. What would the ECU make of that?

Don't want to prolong this. Just passing on my experience

Howdy all,

Thanks for all the feedback.

I had an hour to spend on the car today with my gas analyser.

Note: I am using a Sun MGA 1200 analyser re-calibrated 6 months ago. No doubt the exhaust system will contain a fair bit of combusted crap after the car had run excessive rich for some time.

At idle, I could not get the CO reading at idle to go under 7/8%.

Smokes a bit, some miss on acceleration. Oddly enough I substituted the MAP sensor from a late MB unit, and the thing actually ran better and a little leaner – even at idle? (a little spurious and unconvincing result though)

I appreciate the link to ECU pin chart from Nordfisch. As suggested I’ll take all readings and report back.

Regards,
Rhys

Hi Rhys,

not being able to go below 7-8% means a far too rich mixture. Assuming that you made sure that idle-run contact reaches ECU, this could be caused by

• false air
• injectors leaking ar wrong spray
• broken ECU
• engine temperature sensor wrong or disconnected
• ignition timing is said to have no effect on CO
• MAP sensor (if not completely leaking should not effect CO in IDLE-RUN as well as it is superseded by potentiometer

So yes, you should always measure on ECU connector as Norbert pointed out. That's what I made appendix B for.

Hi Graham,

I did have the experience of what happens to a worn trigger contact during this year myself. 2 of 8 cylinders that were still running when cold, ceased to work when engine got warm.

When plastic cams get worn, the cam on distributor axle will not be able to push them open any more. Should one have some dirt or whatever on either axle or plastic cams, then it would be possible that they open and close several times: i.e. bouncing. That would not really confuse the ECU. It has a Flip-Flop reading these contacts and normally interpretes each closing as a signal from T.C. But it would need more than one contact to bounce as the flip-flop needs one bouncing contact after the other to change its state.Just one bouncing contact would not create that effect. Only if we would see bouncing on both contacts in alteration, it would create an additional injection pulse and it would also wrongly interprete engine revolutions. A flip is like two push buttons. Pushing one button sets the output, pushing the other resets output. In between you can push the first button as often as you like.

On the otther hand if we would come close to 180° closing angle, the 2 contacts on a 4/6 cylinder might overtake each other. However there is a huge tolerance on this injection timing. Fuel just waits before it gets sucked into cylinder.

As a summary: A bouncing would only create additional injection pulses if you had it in such way that it would be bounces in alternation on both contacts. I would see that as rather unlikely.

An 8 cylinder is actually like 2 4-cylinders in parallel, both in T.C. and in ECU.

Hi Volker,

I am proceeding with checking values from the ECU terminal block.

I’ve dismantled an old (Volvo) ECU to manufacture a break-out box as I find the multimeter leads on the ECU terminal contacts leaves some margin for error.

In the mean time, I’m having some difficulty with the pin out sheet with regards to pin 17 (the idle contact on throttle switch). The instruction is to measure against pin 12, but it would seem to me that pin 14 would be the correct pin. Pin 12 is indeed the central distributor trigger point, but with the ECU disconnected, their paths should not cross? (poor extract of Citroen wiring diagram attached).

Do you agree - or am I seeing this wrong?

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,
following the ECU-pinout to be found here at the compendium pin 12 is the ground contact for both sensors - wires connected inside the wiring harness.
Pin 14 is the connecton for the absolute pressure sensor.

Your car doesn't have a full-load-switch.

Be sure to use the correct wiring diagram.

The wiring differs from car model to car model

Regards
Norbert

Mmmm bit of a correction here –

Pin 17 is measured against pin 11 (14 will earth – but not on idle)
Pin 14 (the full load switch) should be measured against 11, but this should be 0 ohm, not infinity (as per instructions) – as the switch is normally closed, and opens on idle vacuum.

Cheers,
Rhys