Die Bosch D-Jetronic war 1967 die erste Großserien elektronische Einspritzung der Welt. - Bosch's D-Jetronic was the first mass-production electronic fuel injection.

Citroen SM doesnt start

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01 Mar 2017 22:39 #6868 by afdahl
Citroen SM doesnt start was created by afdahl
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

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01 Mar 2017 23:11 #6869 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
Tjena Johan,

does the fuel pump also not run for 2 seconds after switching on ignition?
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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02 Mar 2017 08:17 #6871 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
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

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02 Mar 2017 09:44 #6873 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
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.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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02 Mar 2017 10:19 #6874 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
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?

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02 Mar 2017 10:38 #6875 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
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.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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02 Mar 2017 12:39 #6876 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
The pump does run with 12V directly. And The lead to the pump from passenger footbay works.
When I do that the car runs on the minimal fuel from the coldstart for one-two seconds.

But the ECU seems not to run the main injectors. I have tested with another borrowed SM ECU with the same result.
(I have not done the work with removing and testing main injectors yet, just checked cold start injector.)

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02 Mar 2017 18:22 #6879 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
Tjena Johan,

then you need a wiring diagram and follow back from fuel pump to relay and all the way back to ECU. Can you measure on connected ECU, whether it applies ground to pin 19 for 2 seconds after switching on ignition?

I guess that someone has fiddled with the cabling when installing the carburettor button fro fuel pump. Or it might just be classic fault: Is your plus pole on battery firmly tight? There is an additional cable from there to EXU and fuel pump relay that brings +12V to them, If that cable is loose, everything on the car runs, but not ECU and fuel pump. Cold start valve, starter and ignition would run.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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26 Mar 2017 18:51 #7029 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
Tjena Volker.

I must admit that there was some issues with battery connections, but now battery is changed and new connections very solid.

I have measured pin 16 and 24, there is a solid battery voltage.
I have measured pin 19 with ECU attatched and NO signal when switching on ignition.
I have changed relays.

I have tested with full constant battery to running fuelpump with 2Bar pressure, but nothing other than starting on coldstart valve for a couple revs.

I will have to dive into the cabling..... Any SM owner that have electrical schematics for IE model?

Regards
Johan

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26 Mar 2017 19:50 #7030 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
Tjena Johan,

so you measured that the exit of pin 19 to +12V never goes to ground, even not for 1-2 seconds after switching ON ignition.

In that case your ECU is broken and needs repair.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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26 Mar 2017 20:28 #7031 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
Can ECU function intermittent at first and then die completely?
I have tried one other ECU (right number), but have no idea if that one wasnt faulty or not I must admit.

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26 Mar 2017 20:29 #7032 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
I measured it through wire insulation near ECU to ground and didnt get anything when I switched on ignition.

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26 Mar 2017 21:19 #7033 by nordfisch
Replied by nordfisch on topic Citroen SM doesnt start
Hi Johan,
you have to test this using an Ohmmeter, not a Voltmeter.
Did you do it this way?
Resistance has to be almost 'zero' for two seconds when switching ignition on - (continuous during start), then return to infinite Ohms.

Regards
Norbert
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26 Mar 2017 21:31 #7034 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
Aha, I thought I would have a 12V signal through the ECU but obviously the ECU should ground the relay through pin19?
I have no breakout cable so I have to use the needle again to start measure again.

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26 Mar 2017 21:54 #7035 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
No I got almost The Same value with my crude equipment, in the mega ohm range.
Some difference but it didnt fall to zero.

Still The same conclusion about faulty ECU?
Repairing ECU sounds like a lengthy and expensive business. Is Bosch only source?

Regards
Johan

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26 Mar 2017 22:08 #7036 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
Hi Norbert,

sorry to contradict Norbert. Easieast way is to measure pin 19 against +12V. That would show nothing when fuel pump is off and -12V when ECU switches ON fuel pump.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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26 Mar 2017 22:38 #7037 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
Volker you mean zero V or +12V?
I got roughly 12V

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27 Mar 2017 00:23 #7038 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
Tjena Johan,

ECU puts this output actively on 0V to activate fuel pump relay. That is why I say measure against +12V.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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04 Apr 2017 21:24 #7126 by afdahl
Replied by afdahl on topic Citroen SM doesnt start
I have tested with other ECU again and also with a Citroen DS ECU, no change....can it be ECU and is there anyone repairing them? (Bosch)
Is the ecu getting pulse from distributor contacts or ignition coil?

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04 Apr 2017 22:38 #7127 by Dr-DJet
Replied by Dr-DJet on topic Citroen SM doesnt start
Tjena Johan,

well this feature is present in every D-Jetronic ECU. ECU activates fuel pump relay via setting pin 19 to ground in these cases:

  1. for 1-2 seconds after ignition is switched ON
  2. definitely as long as starter is activated
  3. as long as trigger contacts signal a motor rpm of > 250 rpm

So if your ECU does not activate fuel pump relay in cases 1 and 2, it has nothing to do with trigger contacts. Only case 3 is linked to them.
Viele Schraubergrüße - best regards, Dr-DJet Volker
Alles für den Mercedes-Benz R/C 107 und W116 in der SLpedia Sternzeit 107

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