Very rich running and white smoke - 1973 450 SL R107 DJet

Hi All

Feeling very lost chasing a very rich running condition and white smoke from the exhaust on my 1973 r107 450 SL DJet



Smoke tends to be worse upon first start up once warm and then reduces (but still present). Plugs are black (sooty dry plugs)

• Fuel pressure is just below two bar and both air temp and coolant sensor are providing correct resistance readings.
• Map Sensor is holding the correct pressure however looks like it has been tampered with previously (see below pictures) 
• Timing has been checked. 7° BTDC is marked. For some reason when running can only see this mark at 18° mark. However timing is set to 7° BTDC without vaccume (noticed no change in timing when the vacuum line was added. Breaker plate is moving when mightyvac is used)
• Vacuum Smoke Test has been done recently and leaking parts replaced
• The injectors look original and are all firing
• Distributor - When chasing this problem last year, I listened to the injectors and realised 4/8 were not firing. This led me to the trigger points. I replaced some of the blocks and reset all dwell to 120-130 degree range. All injectors are now ticking.
• Can’t see any contaminants in oil
• No loss of coolant or blowback/bubbling in coolant reservoir

Feel it's being massively overfueled. It's been two years chasing this issue since i imported the car, and just want to be able to enjoy it now. Any guidance or diagnostic help is much appreciated! 

Nick





 

Hi Unknown,

we would appreciate if you could sign with fristname so that we can politely address you.

White smoke sounds like ATF. You will find a steel vacuum line from engine to gear box that modulates switching of gears. The actuator there can leak ATF to engine and then you will have huge white smoke clouds from exhaust. Test by removing that vacuum pipe from gear box and close ist.

Hi Dr-Djet,

I will check, however does this also mean i'll be burning rich? The smoke smells (and stings!) like fuel.

Thanks,
Nick

Hi Nick,

Too much fuel should rather make black smoke. But if it stinks fuel, then MPS, water temperature sensor and cold start valve are first candidates to look for.

Hi Nick,

Someone has likely tampered with your MAP sensor. From the factory there is a black cap, but this is now removed and it looks like someone has messed with the screw. That is usually bad news, but sadly not uncommon with US origin cars. Try to locate a “virgin” specimen with the part number 0280100100 that fits your car. Have you checked whether the cold start valve is leaking or stuck open?

Setting timing on your engine should be done with vacuum and then it should be 5 degrees ATDC. You describe that there is no difference with it plugged or unplugged. This suggests a broken vacuum can. The car will still run, but not optimal. I don’t believe it has any effect on your rich running condition. Have you tried measuring your CO values?

Best, Peter

Thanks All!

I'm going to look at ATF and cold start valve.

For the MAP sensor, given that someone has already adjusted, I've been recommended to try adjusting to see if it rectifies any of the symptoms. I believe there is small 7M Hex and then a small slotted screw inside that. Does anyone have any experience adjusting these?

I'll also explore the vacuum can Peter, thank you!

Hi Nick,

there is no slotted screw inside your MPS. And if you play too long with it it will leak. Either through potting or worse through aneroid cells. Then it would be scrap.

This hex screw is highly sensitive. I do recommend not to adjust by trial and error.

Hello, I also have a 1973 450SL from the USA. My car also smoked heavily during the warm-up phase – white smoke! In my case, the cause was broken plastic brackets for the oil spray nozzle on the left cylinder bank. 50-year-old plastic becomes brittle. You can easily test this: Disconnect the black hose on the left valve cover that leads to the air valve and temporarily plug it. Then start the cold engine. It will probably smoke initially, but the smoke should quickly subside once the remaining oil in the intake manifold has burned off. Best regards, Stefan 
 

Hi All, 

A few updates from today: 

Smoke is definitely worse on startup, it reduces once warmed up. 

- Cold start valve looks to be spraying well with no visible leak (see video below). However, any recommendations for the best way to test that it's not continuous firing once running? 

- ATF looks low, I will top this up and monitor levels. No visable leaks but let me know if there's any recommended checks. 

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Hallo, mein test dauert weniger als 5 minuten, deine Versuchsaufbauten bestimmt mehrere Stunden. Nochmal zur Erklärung, auch wenn es hier Stimmen gibt, die behaupten, dass motoröl nur blau raucht - tut es definitiv nicht, wenn genug davon in den Brennraum gezogen wird, dann wirds weiss - und das ist bei nachfolgend beschriebenem Schaden genau der fall.
Besagte Öldusche wird mit Kunststoffhülsen verbunden und in den Ölkanälen des Zylinderkopfs verrastet. Beim Abnehmen der Ventildeckels kann man da durchaus mal dran kommen, z.B. nach dem Ventileinstellen etc.. oder sie brechen von alleine. Wenn sie gebrochen sind, spritzt das Öl direkt auf den Ölabscheider des Ventildeckels. Solange der Zusatzluftschieber geöffnet ist (Warmlaufphase), zieht die Ansaugluft über den Ölabscheider das Motoröl in den Ansaugtrakt vor die Drosselklappe - Rauch. Sobald der Motor auf Betriebstemperatur ist, schließt der Zusatzluftschieber und der Ölstrom hört auf -somit auch das Rauchen. Also ziehe den schwarzen Schlauch vom Ventildeckel ab, und verschließe ihn - ein Lappen reicht! Motor starten und prüfen - sollte aufhören, war zumindest bei mir so. Ich habe dann die Ventildeckel abgenommen und die Schadhaften Verbinder ausgetauscht - seitdem raucht bei mir nichts mehr. VG Stefan

Hello All, 

After some suggestions to look at the oil rail, I took some time to pull valve covers and also the injectors. 

Injectors - I have two injector types, which i feel can't be correct:  0280 150 036 & 0280 150 015. I believe both of them were for the 117 engine, but does anyone know which is correct? Can both types be used? 

Oil rail - Couldn't see anything that concerned me too much. All plastic clips seem to be intact and seated well. 



 

Hi,

0280150015, 024 and 036 all have same color and flow rate. That fits. iF THEY ARE WORKING PROPERLY.

Hi, wenn ich das richtig sehe, bist an der Falschen Seite unterwegs. Du musst auch nicht gleich den Ventildeckel abnehmen, es reicht den Schlauch abzuziehen und zu verschließen - und dann Motor starten. Sicherheitshalber ein Bild im Anhang.