What is this? - PeachParts Mercedes-Benz Forum

JEREMYC · #1 08-06-2006, 10:08 PM

I just got a new to me 83 300cd and I was repairing a few torn and rotted vacuum lines. I noticed one of the vacuum couplers that hook a plastic line from the black box on top of my valve cover to a sensor on my t-stat housing was craked so I tried to replace it. This is my 3rd diesel benz so I am aware of the various things to watch out for. Well I barely touched this line to replace the rubber and a nipple on the sensor broke. I touched the other and it broke too. Can anyone tell me what this sensor is and what it does. It sits next to a temp sensor that hooks into the t-stat housing too. A line runs into from black box on valve cover to this sensor and out of it to something that may be the waste gate maybe?? I think it is the waste gate because it has a small metal flexpipe on it and it looks like has soething to do with the exhaust. Help me please!!!!

techguy512 · #2 08-06-2006, 10:15 PM

Quote:

Originally Posted by JEREMYC

sensor on my t-stat housing......
small metal flexpipe ..... something to do with the exhaust

The thing with the metal flex pipe is your EGR valve, and the sensor on the t-stat housing is a temperature switch which alters the EGR operation depending on engine temp.

Do a search on EGR and you'll find a wealth of information and recommendations.

JEREMYC · #3 08-06-2006, 10:17 PM

Thanks!

Samuel M. Ross · #4 08-07-2006, 12:29 AM

and IF/when you restore it, you might find that the car runs more poorly than it does now. IF this happens, backtrack by putting a golf "T" in the vacuum line that goes to the thermal vacuum switch sensor that broke on you. IF the car runs better, then this is what I meant above.

Even IF you think the car is running well/OK now, I would take the top off the air breather and look down the throat of the intake... and IF you can see where the EGR opens and ports the exhaust gases into the intake, you want to verify that it completely closes when the vacuum is taken away from the EGR. IF the EGR is not completely closing, then this can also add to poor performance, power, and cause black smoke at full throttle.

Sam

JEREMYC · #5 08-07-2006, 10:31 AM

Right now I have just by passed the broken switch. I have temporarily hook the EGR valve directly to the black box on valve cover. It may just be my imagination but it does seem to run better when hooked direct. Would that make sense? I will check it out this evening to make sure the EGR port is closing when vacuum is removed. Thanks for the advice. I will try to post some pics of my beauty here in a few. For $800, it is much more car than I expected.

Samuel M. Ross · #6 08-07-2006, 07:14 PM

at idle it is turned OFF [ zero vacuum to the valve ], and its vacuum source is usually such that a restricted orifice effectively puts it [EGR] in a different pressure zone than the tranny shift control system. Hmmmm... tell me the Year and model and I'll get the Engine Vacuum Diagram. In any event, assuming you have an automatic tranny the EGR vacuum source should be isolated from the tranny shift system... also the EGR opening should be minimal to none at full throttle... so after you start pressing the accelerator, the switch on the valve cover opens the EGR full and it should then start closing as you approach full throttle. If in doubt and as a test, I would put a golf "T" in the EGR line blocking it off so it does not operate at all [ except if it leaks exhaust into the intake manifold]... do this to see if the car runs better than when the EGR circuit is hooked up. IF it runs better when the EGR is disabled, then you should check to see what your State regulations/rules are and then make a decision as to whether to take a chance on leaving the EGR disconnected. Many, many, many of these early EGR's [1980 was the first years here in CA] are disconnected because they make the engine run so poorly with black smoke and a loss of fuel mileage.

Let me know: YEAR & Model, and whether auto or manual shift?
If auto, how is the tranny shifting?
Maybe I can and give you some further help with engine vacuum system.
If you are so inclined to get into this IMPORTANT issue of vacuum control systems, you should invest in a hand vacuum pump that will cost you $40-$60... but having one is essential to such DIY work projects.

Best regards,
Sam

JEREMYC · #7 08-08-2006, 10:54 AM

(snippage)

Let me know: YEAR & Model, and whether auto or manual shift?
If auto, how is the tranny shifting?
Maybe I can and give you some further help with engine vacuum system.
If you are so inclined to get into this IMPORTANT issue of vacuum control systems, you should invest in a hand vacuum pump that will cost you $40-$60... but having one is essential to such DIY work projects.

Best regards,
Sam[/QUOTE]

Thanks for the info Sam. My car is a 1983 300CD Automatic. The trans seems to shift rather quickly. If I am real easy on the gas, it will run through all gears in about 30 seconds or less. Sometimes I pull the shifter back one notch to hold it in 3rd gear a little longer if I need a little extra power. When cold, the trans is allot smoother, almost slipping, than when warm. When warm, it shifts farely hard. On full throttle, I can get a chirp from the back tires while shifting from 1st to 2nd gear. I did not have a BB that could accidentaly find its way into my EGR vacuum line but by the time I was done going through your recomendations, I spent primer from my reloading bench some how found its' way into my vacuum line and plugged it up.. (Not sure how that happened) I couldnt see into my intake after the air cleaner lid had been removed to see if the EGR valve was closing all the way or not but my car ran better after the mysterious pluggage of the vacuum line. BTW, my trans will kick down a gear as needed at full throttle.