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 wrote: 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.