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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Perhaps it could be the thermo-time switch or the #2 temperature sensor shown in pic?

The thermo-time switch controls the cold start injector ( extra one on driver side). Injects fuel during starting for short period only when temperature is low . The #2 temperature sensor is very important. Without that the car would not run well! It is mart of the mixture control. The #1 temperature sensor is on the air intake - It is more important when air is cold.
By the way, the AAV as shown in pic is also important. It is open during cold start and gradually closes until coolant gets to about 150F. They often are sluggish or stuck and cause djet owners grief!

By the way, pic is from Comprehensive Guide in EGv107 in stickies - a must read for new Djet owners :)

 

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Outstanding Contributor
450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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I think it is actually the injector part of the cold start system, but bear in mind that I don't know didly about Mercedes's. This has all been a great learning experience for me. This sensor is located just aft of what appears to be the thermostat housing, but I could be wrong about that too.
The single wire one directly on top of thermostat is 100 c switch for the aux fan.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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The single wire one directly on top of thermostat is 100 c switch for the aux fan.
Right, it is shown in pic. But that one would not have affected the way engine ran. T2 would. TTS would, I suppose, if somehow it kept the cold start injector open.
Interested to know which one it was.
 

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1987 560SL, 2000 Kawasaki W650
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What contact cleaner do you use? I've never found one that worked very well.
Caig Deoxit is the stuff the recording studio engineers use. Dexoit D5 for regular contacts, Deoxit F5 Fader Lube for anything that moves, like switches. I use No-Ox-Id grease sparingly on things like the battery terminals and other exposed electrical surfaces.

The fiberglass pen is great for cleaning thick oxidation on contacts. Wear gloves unless you like tiny little glass slivers on your fingers. One trick I use when cleaning something with heavy oxidation is to put a vacuum cleaner next to what you’re working on to suck up the dirt as it comes off and any glass slivers.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #25
I have cleaned and reconditioned four injectors, and none were plugged. The screens in each were clean with no debris. The injectors themselves were covered with crud. The seals were very brittle. I could blow air backwards through all of them but #6. The dead cylinder was #8. I haven't pulled the #8 plug yet, but the ones I have pulled indicate the engine is running very rich. I will flow test them tomorrow if I have time..
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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If the sensor you were talking about was the #2 temperature sensor, that could be a reason for the rich mixture. Or it could be something else.....
 

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450slc5.0cab 280sl5sp 280se4.5 500se+500slAMG +250seStkW108 350sl4spdX3 500secEuro
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Looks like those injectors have already been redone because they have clamps on the bottom (injector side) that I believe is a crimp from the factory. So the injector-to-rail hoses have been replaced. These clamps look new too.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #29
It all looks new because I replaced the old ones with new ones. I replaced the clamps, the pintels, the hoses, the seals, and the screens. The rest I cleaned. I cut the crimps off with a die grinder, but all of them did not have the factory crimps. You are looking at a rail ready to be re-installed. It was easier to pull the entire rail at once than pull individual injectors. The second injector from the left has a Bondic repaired receptacle - note the clear color.
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #30
I also have new injector harness plugs coming - the old ones just crumbled when I tried to remove them. Once they arrive, I will solder them onto the existing harness and shrink wrap the individual wire connections. I found some for $4.41/each, which if you have searched for them, is a bargain. The plugs in the car are like new Bosch Premium plugs, which I will not replace. I did clean them and set all the gaps to 0.038". The rebuild kit I bought for $77 off the net. The kit came with all new parts as you see them - new TI clamps, hoses, seals, pintels, and screens. For a little over $100, I have reconditioned injectors. A Wilmington Mercedes dealer wanted $1200 to do the same job. The engine is well designed and it is easy to work with individual components. Now I know why Mercedes has so much success in Formula 1 racing.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I also have new injector harness plugs coming - the old ones just crumbled when I tried to remove them.
Besides crumbling, they likely didn't make a good connection. How about the rubber boots that fit over the connectors? Are they still there? They need to be put on before the plug.

BTW, there is a whole thread here about rebuilding harnesses. Brad (aka cush) started it. Based on his research, I rebuilt my harness back as far us the section that exits the firewall. Heat damages the wire insulation as well, so cut back as far as needed.

Regardless of how you do it, it is a good idea to replace the injector connectors. While about it, do the ones for sensors too. This company in Germany can supply the parts at reasonable prices: Repro-Parts including the sensor multi-pin plugs.

The sleevesthat cover the harness wiring are also likely toasted. We used a type sold in USA (covered somewhere in threads below)

Harness thread (later part covers what cush is doing now) D-Jet Engine Harness

My rebuild covered here: Winter/Spring Djet project

How about that 'sensor' you had forgotten to replace - identified it yet?

Having fun?
 

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1974 450SL 1965 Thunderbird 1927 Oldsmobile 1950 Buick 1977 Jeep CJ7J7
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98 Posts
Discussion Starter #32
Actually, I am having fun. I love old cars. I have a 1965 Thunderbird, a 1927 Oldsmobile, a 1950 Buick, and the 1974 450SL. I have sold a 1937 Chevy pickup with 17,000 miles on it, an award winning 1949 Hudson convertible (which I regret selling), and a 1957 Thunderbird. I always wanted a 450SL ever since I saw a good looking blond drive up in a white one at the pool at Mississippi State Univ. My 450SL is also white, and represents the best deal I ever got on a car. The blond, who wound up living with me, wasn't such a good deal. She was evil. Also, the damn car wasn't hers.

That sensor is an injector.

My biggest problem is that I don't know enough about the 450SL to know what is missing, like the boots over the injector plugs. Now I need to get them on the way here before I start splicing wires. I am depending on guys like you and the others to keep me on the right path. I heed all advice, and so far, I have gotten nothing but good advice on this forum.
 
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