Problems with my SM D-Jetronic

First of all, thanks a lot for your site because I have learned a lot about D-Jetronic there. In Spain is not easy to find books about it. I am 41 years old but I like cars older than me and many friends and my father has or has had cars with this injection (Saab 99 EMS, Volvo P1800 ES, VW 411 LE)

I am the owner of a Citroen SM since two years. I have repaired the engine because it consumes more oil than petrol, but now, the engine is mostly brand new.

I have now two questions because it doesn´t works as smooth as a new engine should do.

The first problem is that the engine works too rich when it is hot. Both NTC (air at the air filter and cooling system) are new. What I have observed is that when the engine is hot and you are running at the city, the electric fans works and the voltage at idle speeds is under 12 V. In this situations the engine doesn´t works properly. I have checked that the ECU takes the electricity from the alternator regulator, so I think than maybe the problem is that when it is hot, the voltage is too low for the ECU and it doesn´t works fine. Maybe is better to take the electricity directly from the battery, what do you think?

The second problem is that, when you push the throtle after driving with out pushing it (over-run cut off), the first two seconds the engine misfires like when you have a dirty fuel filter. You can feel it worst when you push lightly the pedal than if you push it harder. I supose that the problem could be with the throtle position sensor, because it cuts inyection like if you where driving in over run mode could be?

The car works very fine when it is cold and while you are driving at the highway, but as soon as you get to the city or in a traffic jam it starts to work so rich that you feel your eyes wants to cry.

What do you think?

Have you got the wiring diagrams for the Citroen SM D-Jetronic?

Best regards and thanks for your help.

Hi Ruben,

Welcome to jetronic.org by Dr-DJet! And hey I have never seen a Saab 99 EMS.They are very rare in Germany.

It is correct that an ECU shoudl get a minimum of 11,5 V to work properly. And I am surprised that it should not be directly connected to the battery. Normally ECU gets it voltages directly form their without fuse via 2 relais. So you should check on pins 16 and 24 hwat the voltages is against pin 11 (ground). A normal alternator should load the battery at 14,4 V .So the voltage should go up to that level when the engine is running.

When it comes to throttle switch and ignition that SM is very special. I always have to check Bosch German documentation what is happening there. From my memory: There are 2 throttle switches. One is for D-Jetronic and one controls an over-run system independent of D-Jetronic. If I remember right, there is also a system to add additional air below certain engine load. Our user iolo (Immanuel) is actually the specialist for this car and I hope he has an English documentation for you on this. I remember that he confirmed that these 2 technical additions are normally broken.

Also the ignition distributor is a nightmare. It has 2 contacts and drives two ignition coils. It is difficult to tune ignition timing of these. Additionally this Marcheval SEV ignition distributor has a proprietary trigger contact cassette that we see nowhere else. It is not a Bosch solution.

So that was just to give you some ideas whar could go wrong. I hope that Immanuel knows a source for English manuals.

Thanks. My car has not the original SEV Marchal distributor. The last owner changed it and now I have the Van Rootselar Distributor wich combines parts from the original SEV and Bosch with electronic triggers for the ignition. For the D-Jetronic uses the same triggers as the original. You can see it here www.sm-ignition.com/en/archives/media/pi...-rootselaar-ignition

This is my friend´s Saab 99 EMS, I love this car, very funny and reliable rubenfidalgo.com/uncategorized/saab-99-e...cion-no-un-flechazo/

Hi,

that is great to see. I never heard of this replacement ignition distributor. Immanuel has even done a repair kit for the SEV trigger cassette. I only have 3 of these test benches shows on the replacement distributor.

Can you ask your friend whether he has spare Saab MAP sensors for me to take reference measurments? I never got hold of any single Saab MAP sensor.

Of course I´ll ask him about it. This car has the third type of MAP with the black plastic cap and the full throtle contact. If we don´t have another spare MAP maybe we can send you the MAP wich is in the car, he has many cars (Volvo P1800 ES is one of them) and don´t use the Saab so often. I´ll ask.

Hi Ruben,

I have asked iolo to join in on this discussion but have not heard of him. I searched my documents and can only find German documents on SM, nothing in English. So my hope is that iolo would return from Easter vacations and then have some documentation.

I found a link to a Citroen SM website that seems to describe this over-run and idle-run stability circuit on pages 48 ff: www.citroen-sm.org/static/Citroen639-7.pdf
Ans also a spare parts list: www.citroen-sm.org/static/Cit612_IE.pdf

Hello, thanks a lot!. I have been with my friend this weekend. We don´t have another air mass meter for the Saab 99 EMS and he left the car in a house he has in another city. Maybe on may I have to go there and bring the part with me to send it to you.

Best regards.

Hi, that would be great!

Hi Ruben,

sorry for the late reply. I've been busy lately.

What I have observed is that when the engine is hot and you are running at the city, the electric fans works and the voltage at idle speeds is under 12 V. In this situations the engine doesn´t works properly. I have checked that the ECU takes the electricity from the alternator regulator, so I think than maybe the problem is that when it is hot, the voltage is too low for the ECU and it doesn´t works fine. Maybe is better to take the electricity directly from the battery, what do you think?

As Volker said, the ECU must be connected directly to the battery. But if you only have 12V something must be wrong. Check your regulator and the alternator. Do you still have the original arrangement (alternator with a separate regulator)? The mechanical regulators are often broken. I would suggest to convert to electronic regulator like this:
Regulator modification
Could also be a weak alternator, the two cooling fans are pulling a lot of power.

My car has not the original SEV Marchal distributor. The last owner changed it and now I have the Van Rootselar Distributor wich combines parts from the original SEV and Bosch with electronic triggers for the ignition. For the D-Jetronic uses the same triggers as the original.

I also have the Van Rootsleaar ignition, which usually works fine.

The first problem is that the engine works too rich when it is hot. Both NTC (air at the air filter and cooling system) are new.

NTC air filter and cooling system properly connected and the plugs were not reversed?

The car works very fine when it is cold and while you are driving at the highway, but as soon as you get to the city or in a traffic jam it starts to work so rich that you feel your eyes wants to cry

This could indicate a dripping or leaking cold start valve. Or the cold start valve is permanently activated by the thermo switch. As long as the engine is cold or the engine speed is high enough, the engine will run reasonably with too much fuel.
In addition, the Maserati engine setup is extremely susceptible to false air.

My recommendation
1. Disconnect and close the fuel supply line on the cold start valve.
2. Close all unnecessary air lines (red markings in the diagram)
3. Do a test drive

The second problem is that, when you push the throtle after driving with out pushing it (over-run cut off), the first two seconds the engine misfires like when you have a dirty fuel filter. You can feel it worst when you push lightly the pedal than if you push it harder. I supose that the problem could be with the throtle position sensor, because it cuts inyection like if you where driving in over run mode could be?

1. That's a known problem. The throttle valve switch must be set very precisely.

2. Open the throttle valve switch housing. The board and the pickups must be absolutely free from any grease !! If necessary clean board with circuit board cleaner only.
3. The circuit board is connected to the plug with spring tongues. These spring tongues often come loose or are corroded at the contact point.
A Bosch Service Point (Koller and Schwemmer) gave me the tip to solder the spring tongues directly to the circuit board.


best regards
Immanuel

Thanks a lot for your help. I have changed the throtle switch wich is mounted on the butterfly of the driver´s side intake manifold. This is de over-run switch and it only has a micro-switch contact inside and only 2 of the 4 pins are connected. The other throttle body is the position sensor for the throtle and the 4 pins works. With the new switch now it runs perfect.

My car has the old regulator type, but with an electronic control inside, like the one you show to me.

First of all I´ll change the wiring and conect the ECU directly to the battery. Then, I´ll check for manifold leaks.

Thanks!!!

Hi Ruben,

You can repair the throttle switch at the drivers side very simply. The micro switch is available at elecrtronics part dealers- it is used in computer mouses. Costs about 4 USD, but the new switch art BOSCH is about 500UUSD. Buy some more of the switches.

Andreas