'73 450 SL electronic fuel injection

[osc]

Hi - That hose goes to the radiator expansion tank onto the little pipe just below the filler cap. (I am waiting for hysterical laughter at this point, but I don't know - is it definately vacuum??) There is no sign of a transistorised ignition unit as I've see on later cars. There are wires coming from the loom towards the coil/ballast resistors - red/black and green/black. There is another wire (purple/red) from the starter 'block' near the battery which I assume is the 12V feed direct to the coil which is live when the engine is cranked. There is another green/black wire going from the coil -ve to the points.
It looks to me that the car does not have electronic ignition....Is this possible please?

i was joking when i said the water washers but maybe i wasn't that far off!!!
ok, i think we have a problem here......can you follow the pipe to the back of the engine bay at tell me where it is connected? if it goes into the inlet manifold it can connect in 2 points. one is a horizontal connection straight down on the inlet manifold that you can clearly see if you get you head back there and the other is tucked in horizontally (use a mirrror and a torch)

both are to the right hand side of where the fuel pressure sensor is mounted and this looks like where the pipe is coming from.

if it is on one of these manifold pressure points then the other end of this MUST go onto the manifold pressure sensor.

The little pipe on the expansion tank is an overflow and there should be a open pipe connected here which will drip any overflow down to a safe place and not squirt in your face. Someone who does not know what they are doing has seriously messed about with your car....

Regarding the transistorised ignition unit. It sounds to me like someone has removed this and as far am i know, your car will not start without it. The Other wires you have mentioned are all correct and the same as mine, but as far as I know you need this unit - are there signs of 4 screw holes and a large hole for the wires to come into the engine bay through the wing? I have a spare unit but it sound like there are a few fundamental issues that need to be sorted before you get to this point.

 

[Alex Crow]

i'm losing strength here, osc, how about you? it will not start without that vacuum connection to the pressure sensor, and the O/P is not trying hard enough to check it out - he/she has been told............

regarding the ignition, i know that this engine in the earlier 108 chassis could have points/condenser/ballast and coil - not electronic. could be the engine or ignition setup has been swapped? malcolm seems to say it may be either depending on age - who knows!

 

[television]

i'm losing strength here, osc, how about you? it will not start without that vacuum connection to the pressure sensor, and the O/P is not trying hard enough to check it out - he/she has been told............

regarding the ignition, i know that this engine in the earlier 108 chassis could have points/condenser/ballast and coil - not electronic. could be the engine or ignition setup has been swapped? malcolm seems to say it may be either depending on age - who knows!

I spent ½ hour on benzworld today and there are many post relating to the change from points in 1973.

Do not forget that transistor ignition was a new thing then and the 107 was first shown in 1971

 

[osc]

Alexander: yes i am being to loose it on this. my car took me agessss to get running right, that fuel pump drove me nuts but this one is beginning to baffle me!

I am a bit confused since my car has points/condenser/ballast and coil AND a transitor box.

This chaps desciption sounds exactly like my car, I still think the ICU has been pinched.

Malcolm: could you send me some links regarding the change from points...i am curious.

 

[television]

I did not keep them,,but later in the day I will go back and look

 

[Isdyldan]

Hi, the pipe which is currently connected to the expansion tank joins the inlet manifold near the bulkhead vertically downwards. (please see photo - it is the braded hose). Are you saying that it should be connected from here to the unit shown in the second photo which is next to the battery on the inner wing please?

 

[osc]

Hi, the pipe which is currently connected to the expansion tank joins the inlet manifold near the bulkhead vertically downwards. (please see photo - it is the braded hose). Are you saying that it should be connected from here to the unit shown in the second photo which is next to the battery on the inner wing please?

Yes this is correct.

1) Make sure the rubber braided pipe is in good condition since it needs to hold a vacuum

2) Can you suck on the pressure sensor inlet connection (use another tempory pipe if you don't want to remove it) and test that it does no leak. When you suck, it should hold vacuum.

3) If possible, remove the plug and measure the resistance across the pressure sensor for (i) pins 1 to 4 (ii) pins 2 and 3

 

[Isdyldan]

Hi - the unit appears to hold vacuum. The resistance accross pins 1-4 is about 90 ohms and accross 2-3 is about 3 ohms.
Regards, Dylan

 

[osc]

Sounds like some progress, but 2-3 should be a few hundred ohms. Can you recheck.

Now for the transistor unit - can you start with some picture of the inside of the distributer (points, etc)

 

[Isdyldan]

Many thanks for your help with this.

I rechecked the 2-3 resistance, and I must have been touching the prongs - I now have a reading of 364 ohms.

Please see attached photo of the distributer.

 

[television]

Yes they are just standard points and not electronic ignition,I take it the cap is out of view under the rotor arm

 

[osc]

ok therefore i still think there should be a "transistorized switching unit" mounted underneath the wing behind the headlight area with 4 wires.....

*brown wire to earth
*green/yellow wire to distributer contact breaker
*black wire to 0.6ohm ballast resistor then goes to coil +ve
*red/black wire to 0.4ohm ballast resistor (and in parallel to starter motor red-violet wire). the other side of the ballast resistor to ignition switch (red/black wire)

can you find it or get one? i have one of these as a spare for my car.

 

[Isdyldan]

ok, thanks. I'll have to try & get one - maybe from Mercman. I had to get a replacement for my first 450 as it had water ingress, so know the unit you are talking about. There is no sign of one on this car. I don't really understand why it is needed, as there is a spark etc, but if it is then I'll have to get one!

 

[television]

I cannot see how you can use points with a transistorized ECU if you have not got the photocell module in the distributor

 

[osc]

This is my conclusion based on the information you have provided and what is fitted to my car. Make sure the unit is from a 450 1971-76 D-Jetronic since I know there are several different types that where on the 350, etc. It will not have a socket on it like the later ones, but instead four wires directly out with the colours I have already indicated. Picture attached. Price from new from USA is around $500. Good luck!

Maybe someone else is able to advise on its function and if you can get it going without - my time is limted to start investigating the unknown.

 

[Alex Crow]

if isdylan needs one we could supply s/h for a lot less.

here goes FROM MEMORY!!

i believe that these early ignitions used points and transistorised switching as osc says, we have a j reg 108 450se in at the minute so will have a look tomorrow, it probably has no cap/condensor.

the electronic triggered later types had a kind of hall sensor and the module had two plugs (not seperate wires with loop terminals), but this was only on k-jetronic systems. as far as i remember there were never photoelectric triggers as MB OE, just as retrofit for eg 280sl pagoda.

as i say that is from memory, but i will get back tomorrow with some facts.

 

[television]

http://www.benzworld.org/forums/r-c107-sl-slc-class/1461941-73-distributor-question.html

 

[Isdyldan]

Thanks guys. I'll have to give this some thought. I have sourced an ignition module, but it is the wrong type which you describe with the two plugs. I can't see how this is any different from any other car with points - points close, coil charges, points open, spark to cap which is distributed to correct plug. It should run.

 

[television]

Thanks guys. I'll have to give this some thought. I have sourced an ignition module, but it is the wrong type which you describe with the two plugs. I can't see how this is any different from any other car with points - points close, coil charges, points open, spark to cap which is distributed to correct plug. It should run.

This is my view as well,,and I would not worry too much, the only thing with the distributors is that the top bearings can where and give erratic running when very worn

 

[Isdyldan]

I think I need to go back to a few fundamentals. It seems I have fuel (wet plugs) and a spark, so it must be timing. I have staticaly timed it to TDC, but maybe I am 180 degrees out at the distributer? How do I tell if number one cylinder is at TDC on the compression stroke please?