R107 450 1973 D Jetronic. Doesn't start - ignition timing problem?

[szamik]

Hello I again need some help.

I have just finished rebuild engine harness in my 450 sl. Now every injectors are working properly so I may think that "electrical" part of Djet works fine.

Unfortunately car still doesn't want to start. Next thing which I decided to check is the ignition. I replaced 8 spark plugs, because they doesn't look good. Also somebody installed 4 electrodes spark plugs, that wasn't good idea - in my opinion :-). Then I checked spark. It was fine on each cylinder so I thought that engine must to start but ofcourse not.

I discovered another important thing. Ignition distributor was loosen, there wasn't even screw in it. This may be problem why car still doesn't start. I think that, because if I change position of distributor , sometimes engine is blocking itself when I cranking. I think that it is happen because ignition is in wrong place. My question, if ignition timing isn't set up properly, there is some chance to start the engine? If not what I should do now? How can I set up ign timing without starting the engine first?

Thanks for help.

[Graham]

Originally Posted by szamik

I discovered another important thing. Ignition distributor was loosen, there wasn't even screw in it. This may be problem why car still doesn't start. I think that, because if I change position of distributor , sometimes engine is blocking itself when I cranking. I think that it is happen because ignition is in wrong place. My question, if ignition timing isn't set up properly, there is some chance to start the engine? If not what I should do now? How can I set up ign timing without starting the engine first?

Thanks for help.

Distributor has to be firmly bolted in place and it's position sets the timing.

For a start, you need to set cylinder 1 at TDC (top dead centre) on compression stroke. At this point, the cams on the #1 cylinder (passenger side front in USA) will be facing upwards like rabbit ears. The pointer down low in front of engine will point almost to the TDC mark on the balancer at front of engine. With engine set like that, rotate the distributor so that the rotor points to a mark on the distributor casing that is at about 1 oclock, when facing the engine. When set like this, the distributor will be almost turned as far as it can go turned counter clockwise and clamping screw will be almost at end of slot. If it is not, the distributor may hav eto be removed and re-installed so it is in this position.

Once in this position, engine should run if you have spark and fuel. Then you need to get a timing light and set the timing so it is at about 0-5deg BTDC at idle (750rpm). The rev engine to 3000rpm and make sure timing advances to
25-30deg BTDC (to show that centrifugal advance weights are not stuck)

[szamik]

Thanks for it.

I set up engine into TDC (I think so, balancer mark into "0" on wheel. I checked cams by looking inside the engine trough the oil cap hole. Both are facing upwards so there is chance that I set up engine properly ). Distributor is set as far as it can go turned counter clockwise. Engine still not start and it is blocking itself while cranking. Ofcourse if I remove main cable from coil to distributor, engine isn't blocking itself at all so I am sure that there is some problem with ignition

I found another thing. When I set up engine into TDC, rotor in distributor cap mark into 4 cyl cable? In my opinion it should mark directly into 1 cyl. Am I right? If yes, we have found what is wrong.

[Graham]

Originally Posted by szamik

I found another thing. When I set up engine into TDC, rotor in distributor cap mark into 4 cyl cable? In my opinion it should mark directly into 1 cyl. Am I right? If yes, we have found what is wrong.

Yes. with #1cyl at TDC, rotor should point to #1 wire which is at about 1 oclock. There is a mark on the distributor casing at that point. If you are not pointing there, then unclamp distributor, pull it up then rotate rotor and push distributor back in until rotor does point to the mark. The gears will cause the rotor to rotate, so you must have rotor pointing more anti clockwise before you insert it. Hard to explain, but just do it and you will see what I mean.

[szamik]

Okey, I set up rotor properly.

There are small succeses. Engine doesn't block itself while cranking and also it almost start :-)

Almost... Engine is trying to catch only if I press gas pedal almost to the metal. I found that throttle switch is also unscrewed and I can change it position.
Is this part needed to start the engine?

I will be trying more tomorrow, because battery is gone

[Graham]

Originally Posted by szamik

Okey, I set up rotor properly.

There are small succeses. Engine doesn't block itself while cranking and also it almost start :-)

Almost... Engine is trying to catch only if I press gas pedal almost to the metal. I found that throttle switch is also unscrewed and I can change it position.
Is this part needed to start the engine?

I will be trying more tomorrow, because battery is gone

Yes, you need to get the throttle position switch properly set. This link explains how to refurbish a TPS, but at least lock it back in place and set it with feeler gauge as described near end of pdf.

If engine won't keep running, try squirting some fuel into intake. Could be there is a problem with fuel injection system (trigger points for example)

Sounds like you should go read some of the D-Jet stuff on BW. Links to shop manual and other stuff there too:

Throttle Position SWitch - Early D-Jets. - Mercedes-Benz Forum

For general 107 stuff including section on Djets: The Encyclopaedia Germanica Volume 107 (aka EGv107) - Mercedes-Benz Forum

One owners attempt to cover most things we djet owners run into: The Comprehensive Illustrated Djet (72-75 350-450SL) Thread - Mercedes-Benz Forum

and this early training manual from Bosch: Early Mercedes Bosch D-Jetronic Training manual - Mercedes-Benz Forum

Good Luck!

[szamik]

Thanks a lot for this.

I set up properly TPS. There is 10 changes from 0 ohm to infinity when I press throttle pedal so everything is as it should but car still doesn't want to wake up. Engine is trying to catch but nothing else.

8 injectors starts to working while start cranking the engine. Cold start injector too. I measured level of fuel which goes out of each injector. Level is the same for each. So I may think that trigger points are okey. Also I was trying to squirt fuel into intake - no changes.

Spark? Nice and bright on each cyl so probably coil, distributor and battery (it's not in perfect condition,because after few tries it's dead but I think that it is not a problem) are okey. Plugs are new. After cranking they are still completly clean - without any symptom of burn but I can smell and see some fuel on them - illogical :/



Two things that may be a problem in my opinion. Potentiometer on ECU? Somebody changed it position because I see some scratches on it. I twist it into the middle of scale. I read that this potentiometer is for fuel ratio at idle, but while cranking engine too?

Second thing is a screw which is using to setting up idle. Also somebody changed it position. Here I don't have idea how I should set up this screw to start car

[Diseasel300]

I don't know anything about the D-Jet system, but if the plugs are wet after cranking and you know you're getting a good spark, it sounds like you're flooding (way too much fuel).

[Graham]

Originally Posted by szamik

Thanks a lot for this.

I set up properly TPS. There is 10 changes from 0 ohm to infinity when I press throttle pedal so everything is as it should but car still doesn't want to wake up. Engine is trying to catch but nothing else.

8 injectors starts to working while start cranking the engine. Cold start injector too. I measured level of fuel which goes out of each injector. Level is the same for each. So I may think that trigger points are okey. Also I was trying to squirt fuel into intake - no changes.

Spark? Nice and bright on each cyl so probably coil, distributor and battery (it's not in perfect condition,because after few tries it's dead but I think that it is not a problem) are okey. Plugs are new. After cranking they are still completly clean - without any symptom of burn but I can smell and see some fuel on them - illogical :/



Two things that may be a problem in my opinion. Potentiometer on ECU? Somebody changed it position because I see some scratches on it. I twist it into the middle of scale. I read that this potentiometer is for fuel ratio at idle, but while cranking engine too?

Second thing is a screw which is using to setting up idle. Also somebody changed it position. Here I don't have idea how I should set up this screw to start car

ECU potentiometer is only a fine adjustment, so starting with it in center is fine.

When you adjusted TPS, did you make sure to adjust the idle position so it signals to ECU when throttle plate is closed?

When you checked spark, was this with plug wire connected to actual plug?
And you got strong spark on plug?
Points set to about 0.014" gap?
Are your wires connected correctly?


The position of the idle screw (located next to AAV) is dependent on other things such as leaking AAV and other air leakage. But for a start, you could set it at about 1.5 to 2 full turns open. Only affects idle rpm.

Have you measured and set the fuel pressure? You must do that so you know you have ~30 psig in rails.

You may need to test all your sensor resistances for proper values and continuity at the ECU end of your new harness. This check should especially include the two temperature sensors & the MPS but while there everything else as well. Engine shop manual section 07.4 has section on how to do this with multimeter. Also do vacuum check on MPS.

If you think you are flooding, try disconnecting trigger points or injector leads and try starting with just fuel squirted into intake. Doubt that is problem if plugs are just a bit wet. More like they are not firing, at least at right time.

Double check your timing is approx right and not 180deg out: #1 cyl (passenger front in NA) cam lobes sticking up like rabbits ears with balancer pointer at close to TDC and rotor pointing to #1 wire position in distributor.

[szamik]

Benz finally start :-)

But... Engine starts, only when ignition cap is turned maximum clockwise direction (fully retarded ignition?). In the effect of that, engine runs very badly. Smokes a lot. Plugs after a while are covered by unburned fuel.

When I am trying to advance ignition just a little bit, there is no chance to start the engine.


Again need you help


One thing that I discovered is that sideslip in contact breaker is not in good condition - in my opinion. What do you thing? This may be a problem? Few photos:




And the engine start only with cap in this position:



This is how it runs and start:

https://www.youtube.com/watch?v=E2Nr6nhmxz8

https://www.youtube.com/watch?v=Awu9av5Gq10

[Graham]

Are you sure you have a 1973 model? What part of the world is car from? The distributor looks different from this one which I believe is out of a 73 450SL:

Your distributor:


Your distributor has the vacuum pod arm on the other side. I believe 1975 model had that type of distributor with 2 ports on vacuum pod - advance and retard.

Some other comments:
- that heavy wire going to the blue screw does not look original. It could prevent the upper plate from moving. Normally there is a thinner braided wire that connects the upper and lower plates and it is off to the side.
- I don't know what you mean by sideslip. Make sure you have a new set of points and that initial gap is set to about .014" or install a Pertronix 1885 electronic points replacement and forget about the points!
-If you keep the points, you can cut the wire going to the condenser (Red Dot in pic) and remove the condenser. It is not needed and most cars had them removed because they can cause problems.
- The screw location on the distributor clamp seems to show that the distributor casing is turned almost fully counter clockwise and timing would be advanced. But you say it has to be turned clockwise and fully retarded for engine to run? I am confused. If rotor points to #1 cyl mark on casing when engine is at TDC, then clamp should be about where your picture shows it for timing to be close to correct.

[meltedpanda]

you got the right expert helping you, but few other things to think about- has anyone messed with the timing chain, have you checked that TDC lines up with marks on the cam?
Fuel pump - original or after market? ( fuel pressure is important on these) spin up and stop when key goes to "on"
Did you check the cold start valve for proper function? turns on and shuts off?
AAV open and closes properly ( should be open at start)

[szamik]

Originally Posted by Graham

Are you sure you have a 1973 model? What part of the world is car from? The distributor looks different from this one which I believe is out of a 73 450SL

Yes, car is from 73. It was made for EU market so maybe this is the reason of differences.

Originally Posted by Graham

that heavy wire going to the blue screw does not look original. It could prevent the upper plate from moving. Normally there is a thinner braided wire that connects the upper and lower plates and it is off to the side.

You mean this wire in blue circle?



I don't have it in my distributor. Here is better picture how it looks in my car:



I removed wire which you are talking about and i tried to start the engine. It start and dies immediately when I relased the key, so I think that it must be connected as it was :-)Also I found that I don't have this clip (yellow circle) on arm.

Originally Posted by Graham

- The screw location on the distributor clamp seems to show that the distributor casing is turned almost fully counter clockwise and timing would be advanced. But you say it has to be turned clockwise and fully retarded for engine to run? I am confused. If rotor points to #1 cyl mark on casing when engine is at TDC, then clamp should be about where your picture shows it for timing to be close to correct.

Yes, it was my mistake :-) Ofcourse I was mean that distributor i set up COUNTER clockwise.

Originally Posted by meltedpanda

you got the right expert helping you, but few other things to think about- has anyone messed with the timing chain, have you checked that TDC lines up with marks on the cam?
Fuel pump - original or after market? ( fuel pressure is important on these) spin up and stop when key goes to "on"
Did you check the cold start valve for proper function? turns on and shuts off?
AAV open and closes properly ( should be open at start)

Marks on cam? No, I haven't. I'll check it tomorrow.

Fuel pump oryginal, it works well. Fuel presure is good. Injectors too, i checked them outside of car.

AAV is fixed. It was stuck but after cleaning it starts to work. I checked it in hot water. Works well.






Edit:

I broke something again :-) Engine starts and dies when I relased the key. It's not the problem with triggers because when I put some fuel directly into throttle body it happens too.

Tell me one thing. Ignition coil shoud have +12V on "+" terminal when I switch key to ignition? My doesn't have and also "-" is connected directly to the fender... In different cars coils have constans + on ignition and - is connected to breaker in distributor.

[Graham]

I checked and the EU 1973 distributor had part number 0231403004. It looks like this one (which seems to be the one you have):



There are two connections on vacuum pod. One for advance and one retard (at least on later cars). The specs for your car say to set timing at about TDC at idle with vacuum connected and 30deg BTDC at 3000rpm (vacuum disconnected and plugged). I don't know exactly how the vac advance retard works - do you have two tubes coming to the vacuum pod?

Yes the blue circle is the flex wire. It should connect between the upper and lower plates and be flexible enough to allow upper plate to move. Maybe install a thinner braided wire. This is how original looked on my car:


You should have a circlip in yellow circle.

Metedpandas suggestion to check static timing is good. With marks on passenger side cam lined up, cams on #1 pointing up, pointer on crankshaft should point close to TDC and the distributor rotor to mark at #1 . Always good starting point.

The way engine cuts out when you release starter may point to a wiring problem. During starting 12V comes from terminal 16 and bypasses the 0.4ohm resistor. Make sure you have 12V on the line coming from the ignition switch (turn it on without actuating starter - you should hear fuel pump run) The ignition wiring for the Djet is not same as other cars. This is diagram. Shop manual has check-out voltage locations - I will try and find a link.

[Frank Reiner]

Graham:

Just a thought: 1973 may have a four pin amplifier (switchgear), which switches the ground side of the coil, or since it is non-North America, there may not be a switchgear at all, just standard points controlled ignition.