Citroen SM injector points

Hi Rhys,

I've checked the secondary throttle switch, it is only for the additional throttle switches and idle-speed control.

So we are left with

1. Cold start valve
2. False air leakage -> Use brake cleaner to check if engine speed would change
3. Leaking injectors -> Make spray test and replace rubber sealings
4. Completely misadjusted ignition timing
5. Finally ECU

Hi Volker,

Yes, secondary switch only operates electro valve to operate vacuum actuator - to close secondary throttle butterflies at idle. All adjusted and working ok (unusual for I.E. SM).

I have disconnected cold start injector lead to isolate the cold start injector as being a possible cause while testing this mixture issue.

Even though type 1 MAP sensor seems OK - idle still runs rich (with adjusted idle switch) - so I rule out MAP sensor for now.

So -

1. Re-test all connections with brake cleaner and look for change in engine speed.
2. Re-adjust ignition timing (not touched for a while)
3, Suspect ECU
I will contact local company that repaired/tested ECU previously. What questions must I ask to understand that they know what they are talking about, or that their testing is adequate?

Thanks again,

Rhys

Hi Rhys,

it is not enough to electrically disconnect cold start valve. You should disconnect it from fuel as it could be leaking even that is is electrically diconnected.

Regarding your ECU: Ask them how they verified proper function after repair. Did they check all function block's operation against references? Maybe you can find someone with the same type of ECU down under. That is easier than sending it to Europe for verification.

Regarding ignition timing:

It is not enough to just adjust it at one point. You must also verify that ignition timing speed and vacuum adjustment works properly. Therefore normally workshop manuals normally contain a value for adjustment plus 2 for speed reference and vacuum advance.

What about air leakage and injector spray test?

Hi Rhys,
one more idea: What about the vacuum tube towards the full-load-switch?
Some models have a calíbrated, very close borehole in the intake manifold that could be blocked.
The full-load switch would then constantly send 'full load'.

Regards
Norbert

Hi Norbert,

The full-load switch has no restriction in the hose. It draws from one of three tubes on the LH plenum (Decel, full-load , MAP sensor). Tubes are ok, but the switch being isolated removes the possibility of earthing pin 14 and the ECU fully dosing.

Hi Volker: I will undertake all that you recommend.

Is this a foolish idea? Remembering that even at idle - my mixture is too rich. Would assessing the running vehicle on a Volvo 164 ECU (which I can access) - on idle circuit only, be a way to isolate a ECU dosing problem? I can work out differences in the injector pin-outs......and the mother boards seem similar?

Cheers,
Rhys

Hi Rhys,

that is too difficult to answer right away. I will have a look at it tomorrow. Is there no SM club in AUS where you would get another ECU for testing?

However I would also need the Volvo ECU no, as there are several.