1975 350SLC rebirth

Dear Volker,

Thank you!
Well I have reached the stage where I would be grateful for some advice / suggestions!
A bit of background first. The car is generally in great condition, with 35000 kms on the clock, believed genuine. The camshafts are like new and the timing chain only shows very minimal stretch. However it has been parked for about 20 years and I have no idea if it ran when park.
Before attempting to start it, I set up a fuel feed from a jerrycan (I intend to fit a new fuel tank). Fitted a new fuel pump (3 bar operating pressure) and filter. Flushed the fuel lines on the car. Changed engine oil and filter. Adjusted valve clearances. Checked distributor on the bench, cleaned points and cleaned injection trigger contacts. One out of 4 was not working but I got that going. Checked and cleaned TS on bench. Checked MAP holds vacuum 0.5 bar.Fitted new plugs, Checked fuel pressure at cold start connection 2.2 bar on my guage. Checked for spark very good. Then attempted to start . Pump runs a few seconds when turning on, and also runs when starter motor is activated. Engine does not start, but will run when carb cleaner is sprayed in the intake. At that stage I tried to feel for vibration / noise on injection valves nothing. I then checked if there is any voltage at the injection valve socket, on a 1 volt scale, absolutely nothing, I did this on cylinders 1, 2 and 3
Then I followed all the checks in section 13:
12 volt present on pins 16 and 24, start signal on pin 18 also good. Temp sensors, TS, MAP all read correct values.
Fuel pump control between pins 19 and 16 shows 52 ohm, which is more than a few... But the pump seems to do what it should do.
Now of course I am starting to think that the ECU is faulty!!! As it does not fire the injectors!
Have I missed anything?
Many thanks,

Jean Pierre

Hi Jean-Pierre,

I opened a new thread as you had put it in Introduction.

Now when it comes to non-firing injectors. That can have many reasons:

1. Injector needle can stick inside. Can mostly be repaired by cleaning.
2. ECU can be broken
3. Wiring and / or grounding can be faulty
4. Steering wheel on wrong side
   
   - don't take me serious on that

Injectors must fire during start but of course engine vibrates and you can hardly feel their tickering while cranking engine. But try the following: Ignition ON - not too long as this might burn ignition module and / or power resistors - and push down gas pedal. You should hear injectors tickering. And disconnect ECU connector and measure pins 3, 4, 5, 6 against ground. You should see 1,2 ohm plus a bit for wires.

Dear Volker,

Many thanks for your reply, I have only just found it as it is a different thread now...
The ECU has already been sent to England for checking / repair.
I will of course keep you posted but it will take a few weeks before I get it back!
I will check those pins tomorrow.
Surely one should see some voltage at the injector plugs on a 1 volt scale while cranking?
I tested cylinders 1 2 and 3 which are in 3 different groups...
The only sign of life is from the cold start injector, plus of course the engine runs when starter motor is activated and carb cleaner is sprayed in the intake.
When we got the car the whole fuel pump / filter assembly at the rear was missing altogether, which leads me to think the car had a problem when it was parked... Or it could have been stolen while in storage!

Best regards,

Jean Pierre

Hi Jean-Pierre,

interesting I know of no one in the UK who would have all reference values to test each function block before and after repair.

Dear Volker,

The ECU went to the UK, was tested and found to be working perfectly...It's now back with me.
So I decided to test everything again from the ECU plug

PIN
1  351 ohm @ 17 degrees  air temp sensor
3  1.4 ohm to ground  output injectors group1
4  1.4 ohm  output injectors group 2
5  1.4 ohm  output injectors group 3
6  1.5 ohm  output injectors group 4
7  to 15 88.9 ohm to ground open  MAP primary coil
8  to 10 334 ohm  to ground open  MAP secondary coil
9  to 12  open then on and off while pressing throttle slowly  TS
13  on / off while rotating engine trigger contact 2
14  on / off while rotating engine  trigger contact 4
16  12.35 volt ignition on
18  12.35 volt start position
19  to 16  58 ohm  output to fuel pump relay
20   open then on and off while pressing throttle slowly  TS
21  on / off while rotating engine  trigger contact 1
22  on / off while rotating engine  trigger contact 3
23  2.95 kilo ohm @17 degrees  water temp
24  12.35 volt ignition on

So everything looks normal apart from 19 against 16 you say should be only a few ohm, I get 58. Is that bad? However the pump seems to behave normally, it runs for 2 seconds or so when ignition is switched on, it also ran when the starter motor was cranked.

I say ran because the starter motor has decided to stop working, I need to look at it on Monday. Therefore I could not try to start the car.

Next stop I guess, check the injectors?

There are 5 relays above the fuse box, I am not sure which one is the fuel relay, what do I need to check there?

Jean Pierre

Hi Jean-Pierre,

do you have a test protocol from the UK how and what they tested? I am curious whether they know what they are doing and whether they test each function block.

Have you ever tested fuel pressure and does fuel pump run for 2 seconds after starting? Fuel pump relay resistance is okay.