Injectors doesn't inject

Hello,
i'm new on this forum.
I have a problem with my '75 mercedes 450 sl.
The injectors doesn't inject.
I’ve used the website as a guide to check my ECU unit.
After this i may assume that my ECU is broken.

- I’ve checked the power between pin 11 and 16, 11 and 24.
These are both 12,25 as u can see in the attachments, so i think these are correct.

- I’ve checked the trigger contacts between 12 and 14, 12 and 14, 12 and 21, 12 and 22, and they all give a good signal. (see attachments)

- I've also checked if there is a signal between pin 12 and pin 25, but also here i measure nothing.

Dispite this all, there is no constant signal on my injector outputs, (see attachments).
Other components like my fuel pump does work perfectly.
Is there something else that i have to check, to be sure my ECU is broken?
If i'm sure it is broken, is there a possibility to just get a ECU from the scrapyard, with the same partnumber?
Thanks in advance!

Hi Ward,

your dwell on trigger contacts seems to not the same on all the contacts. While dwell does not really matter, I would propose to align trigger contacts. And it is much better to measure all 4 trigger contacts at the same time with a 4 channel oscilloscope. Then you can also monitor the 90° between all 4 of them.

Your pocket oscilloscope seems to be on wrong trigger or it cannot handle injection pulses. I cannot see a single good one and I believe it is due to your measuring method.

Sorry,

read your thread again. If injectors do not inject at all (no vibration / sound) and your MAP sensor is connected electrically to ECU, and if your measured trigger contacts on ECU connector as well as 3,4,5,6 then it is your ECU. You can use any with the right Bosch no. But I doubt you will find one on scrap yard.

I've tried to switch the ECU unit, with a working one, but still the same.
The injectors won't inject, I've placed little cups underneath the injectors, but there is no fuel at none of them all.
Tomorrow i'm going to check all mass connection.
Does anyone has another idea what the cause may be?
Thanks in advance!

Hi Ward,
yes, check the mass connection of the injectors, located on the top of the engine.
All injectors are connected to one single point.

In measuring the injector's resistance at the ECU-plug you can check the connectivity, too.

Regards
Norbert

Hi Ward,

as I wrote above: If you measured pin 13,14,21,22 (trigger contacts) at ECU connector and if you also measured pins 3-6 then you know incoming and outgoing contacts. Also measure pin 24 to have +12V to pin 11 . Otherwise injectors wont operate.