Citroen SM doesnt start

Hello.

I have bought myself a Citroen SM injection, it did run but had stuttering in high revs.
When I should go for anual inspection i died on me, impossible to restart.

It has a lumenition ignition system, which i have checked and have spark.
I have tested fuelpump for function and pressure, and set it to 2bar.
My hoses isnt the newest.

Now to the issue.
The ecu doesnt seem to "drive" the pump at all. When I wire it separetaly the car seem to make some revolutions on the cold start but then dies.

Regards
Johan Dahl

Tjena Johan,

does the fuel pump also not run for 2 seconds after switching on ignition?

No thats the problem, nothing.

The car have been converted and backconverted to and from carburettors....and fuelpump works when operating key when using that big carburettor relay.
But obviously doesnt run when connected to the singlelead comming from the wireharness going to and from ECU.

Regards
Johan

Hi Johan,

that means fuel pump only runs when you switch the extra button. And it did run on ECU before? You never know what modifications were made. You need to check them first. So your car would run with the extra button for activating fuel pump?

Other than that fuel pump is controlled by pin 19 of ECU. When ECU wants fuel pump to tun, it apllies ground to pin 19. That activates a fuel pump relay which then sends +12V to the fuel pump. So cables and relays can also be a problem.

Hi Volker.

Thank you for help.
I have applied 12V directly to pump but it will not start, just doing a couple of revs on the coldstart injector. (I believe)

(No extra button for it to run, just the relay that was installed into the carburettor cars.
That one was uninstalled when they switched back to injection.)

Thank you! I will work with ground,harness and relays.

It isnt any more "conditions" for ecu to switch on the pump?

Hi Johan,

if your fuel pump does not start when applying +12V, then it is broken, cables are broken or ground is corroded. In that case ECU can also not start it.

Normally ECU applies ground to fuel pumpe relay in following condictions:

1. For 1 - 2 seconds after igntion is switched ON. Then it ceases. You should hear the pump.
2. During cranking starter
3. When engines runs at a speed of more than 300 rpm

That can of course fail, but when your pump does not run when directly applying +12V to it, look for the fault there.