thermo time switch

[greythunder]

from what i'm reading about this part it controls the fuel enrichment until the engine gets to temperature. it would make sense this may be the problem with my 92 300d 2.5 because it starts rough, missing and such and then it's fine after getting to temp.

can anyone tell me where this part is located on the engine, and if there is a testing procedure.

Mercedes® Thermo Time Switch, 1977-1993 - Mercedes Parts And Accessories

[compu_85]

The thermo time switch is only used on gas cars.

-J

[Mxfrank]

This function is handled by the EDS system, which is a pretty complicated thing to troubleshoot. Doesn't usually go bad. There's a solenoid on the back of the IP that controls the position of the rack, a computer behind the battery, various temperature sensors and the air mass sensor. It's not covered by the FSM, the documentation is in one of the service bulletins. They're available through WIS-net, but I think you have to pay for access.

[compu_85]

That solenoid is used to control idle speed, and yes the EDS computer looks at coolant temp to see what the idle speed should be.

If the motor is missing when cold I would look at the glow plugs, injectors, and injector timing.

-J

[greythunder]

thanks for all the replies!

I replaced the glow plugs and reamed the holes yesterday, and im getting 12.5V at on each pin at the gp relay. I replaced nozzles and pop tested a few months ago. maybe the glow plug temp switch?

it has done this miss/rough start since i have had it. with all i've done so far it has helped a ton with power and smoothness, when it's warm. but it's almost like one of the cylinders isn't firing when it first starts.

Question, what is the single pin sensor to the left of the engine fan in what looks like the block on the front?

[Mxfrank]

There are probably two thermo switches there, one is tucked under the manifold and behind the the thermostat, the other where you can see. The one you can see I believe is for the afterglow function, the one towards the rear I believe is the EDS switch. These aren't sensors, they are switches...set to turn off a fixed temperatures. Don't hold me to the function, it changes from year to year and model to model.

[big d]

I have a same problem with my 1992 300D.It idle fine til afterglow cycle is done than it start missing.After it warm up it work fine.

[dieselbenz1]

The one one the left under the tensioner bolt is a temperature sensor used for glow plug duration. I can't recall the resistance verses temperature but I believe it can be found with a search. The other sensor on the right higher up is another temperature sensor used to control the auxiliary fans. In my case 92 e300d they are not interchangable.

I do know if you put a 1 k resistor in place of the glow plug temp sensor the after glow is maximum. If you do this and your engine runs normal until the after glow goes out it would point to perhaps pop pressures being wrongly set as was in my case.

[greythunder]

is the glow plug temp sensor the one directly under the glow plugs of cylinders 1 and 2?

[dieselbenz1]

No that is the auxiliary fan sensor
Glow plug temp sensor on passengers side lower down close to the front

Sorry about my confusion in my last post I assumed left right as you are facing the engine from the front

[greythunder]

thanks for the clarification.

I think I may have figured out the problem, and boy do I feel like a tool. It made sense to me that once changing the glow plugs after 130k miles, that it started worse and rougher because they are pulling more power from the battery. I tested the voltage at each one during the glow plug burn cycle and noticed the it started at 12.5 volts then quickly fell to 9 volts over the course of 5-6 seconds.

this morning I got up with the engine cold and hooked my jeep battery up to the Mercedes battery and "jumped" it.

almost no missing or rough idling.

I think I just need a new battery. the one on it is one that was on the car when I bought it and the guy said he put a new battery in it recently 'just to get by'. he said he couldn't find one that was listed for the car. it only has 615 cca.

what should I be looking for in a replacement battery?

[dieselbenz1]

I can't recall the exact model but when I had replaced mine there was only one equivalent third party identical to the OEM size for cranking power and physical size. I think international brand but I am completely satisfied 7 yrs latter and going strong.

[dieselbenz1]

The glow plug duration is based on engine temperature and 12 plus volts are supplied to the glow plugs for that time period. Then the afterglow kicks in again for a time period based on engine temperature but only 9vdc go to the glow plugs!

[greythunder]

I got a new battery, a huge 1080a/900cca unit from napa.

definitely helped a lot of things. at idle with the ac on it no longer feels like a full body massage sitting in the seat, and the transmission seems to shift better, weird I know bc it's vacuum controlled.

however, the rough start up is a good bit better, but still persists. I have been able to identify 4 what I think are temp sensors/switches. any help on identifying them for troubleshooting would be helpful.

the ones I will call 1 and 2 are on the top of the engine close to the upper radiator hose 1 is 2 poles the other 1 pole.

#3 is under the glow plugs of cylinders 1 and 2 and is one pole

the other is I think the one referred to above on the left front of the engine kinda down low. I haven't been able to look for the one closer to the thermostat housing.

I called the stealership and the parts guy and I had a hard time trying to identify what they were by their location, and he found one that he said was the only one in the country's inventory and it was $210

I almost forgot to ask if I need to be ready for coolant to gush out of all these sensor's holes when they are removed? the one under the glow plugs follows the glow plug harness back to the gp relay.

[dieselbenz1]

What you refer to as 1 two poles is for the auxiliary fans. Number 2 one pole is for the temperature gauge. Number 3 I don't have this. By thermostat on opposite side of engine is glow plug sensor.

Yes a bit of coolant will leak just be fast!