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  #1  
Old 11-23-2010, 06:23 PM
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Join Date: Nov 2010
Location: Vermont
Posts: 12
More 300D Vacuum Problems

Seems that everyone is having vacuum issues with their mercedes diesel's.
Here's my story:
My 1993 300D was shifting rough and the vacuum flap on the boost control that the Y/27-5 switchover valve outputs vacuum to was not opening all the way.
Easy things first, I calibrated the boost valve using a hand operated vacuum pump, it was nearly spot on so I didn't touch it.
Looking at my vacuum lines, they all looked like they were in sad shape, some of them could be pulled apart by practically breathing on them.
So I took a few hours and replaced every single vacuum line in the car. Took it for a test drive, and it shifted far smoother, nearly as soft as a brand new benz. I though "success!" and popped the vacuum gauge on to the vacuum control valve (#65 in the vacuum line routing diagram) and prepared to dial in the vacuum there to further improve the quality of my shifts.
That's when the real trouble began. I discovered the vacuum pressure was still far short of what it should be. So after another hour or so of plugging lines and following the maze of lines around, I have isolated my problem to the area around the ARF Vacuum Transducer (Y31/5).

I have no idea what the vacuum transducer does so I do not know how to diagnose my problems here.
The symptoms:
With everything on the left side of the 4-way connector (61d) disconnected, I have a vacuum pressure of 21 inHg in the system.
Connecting everything up to the transducer Y31/5, I have about 19 inHG.
So, about 19 inHG enters the transducer, typically around 8 or 9 leaves it, but this number varies. Also, the boost control valve no longer moves under hard throttle, it always remains closed.
So the net of my efforts has been to get smoother shifting at the cost of loosing all of the boost.

I noticed at one point that when I reached down, wiggling the wires and tubes, the pressure would fluctuate, often increasing. So I played around with that a little and it seemed to change the most when I moved the wires. So I thought it might be an electrical issue. The contacts were corroded, so I applied electrical contact cleaner. That didn't help. So I replaced the last 10 inches or so of wire before the plug and the result of all this was that now I don't get the fluctuating pressure when I bump wires and tubes, but the pressure reading is still far too low.
I have read that the transducer can be swapped with the other one to see if it is faulty, so I tried to do that, but unfortunately one of the bolts on the upper one is very stuck so I can not remove it without risking damage to the working transducer.
Anyone have any ideas?
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  #2  
Old 11-23-2010, 06:30 PM
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Mama's 300D
 
Join Date: Jan 2008
Location: Missouri
Posts: 482
Sorry, no, I'm having issues, too, but where the heck did you get a diagram of your system?? I'd sure like to find one for my 81 300D! At least then I could get an idea of the system make up, anyway. (Good luck on yours, by the way)
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***********************************


1951 Chevy 3100

2003 Indian Chief Roadmaster

1983 GMC 1 ton Dually

1982 Chevy 1 ton Dually, service body (sold)

'90 GMC Suburban 6.2 "SS Veg-Burban"
(single tank WVO\diesel conversion) SOLD

'81 300D ~ Mama's car...my job (now my car)(but still my job) SOLD

'83 300sd ~ rescue car SOLD

2005 Ford Taurus (Mama's new car)(NOT my job!)
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  #3  
Old 11-23-2010, 08:35 PM
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Join Date: Nov 2010
Location: Vermont
Posts: 12
RE: Showme

Check out Diesel Giant for a troubleshooting guide, I believe it's for your model. It feels kind of like they want to sell you lots of parts as you read through it, but it gives you the basics anyway.

If you have an autozone nearby, you can rent a vacuum pump for free from them so there's no need to buy one. I had to buy a vacuum gauge to do my troubleshooting, but for about $10-20, you can purchase a real nice easy to read one.

Diesel Giant tutorial:
http://www.dieselgiant.com/mercedesvacuumtroubleshooting.htm

also:
http://www.mercedesdismantlers.com/diesel_vacuum_system
has some vacuum diagrams


As for diagnosing problems, there should be a multi-directional (most likely a 4 or 5 way) connector somewhere at the heart of the system with one of the directions going straight into the vacuum pump built into the engine. Start there, disconnect and plug all the directions except the one to the pump and then connect them back together one at a time, testing with a vacuum gauge as you go, and it will help you locate which branch or branches of your system is/are not maintaining the correct vacuum pressure.
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  #4  
Old 11-23-2010, 08:49 PM
showme's Avatar
Mama's 300D
 
Join Date: Jan 2008
Location: Missouri
Posts: 482
Thanks very much for the info. I have a mity vac, just never used it before this, so I'm learning as I go. Your instruction helps, though. And I will check out dieselgiant. I found something on the search today on a site called peterschmit.com, but it's not close to complete, just the egr to the ip. Thanks again, and hope you get yours back in order. Lee
__________________
"Knowing is not enough, we must apply.
Willing is not enough, we must do." Goethe

***********************************


1951 Chevy 3100

2003 Indian Chief Roadmaster

1983 GMC 1 ton Dually

1982 Chevy 1 ton Dually, service body (sold)

'90 GMC Suburban 6.2 "SS Veg-Burban"
(single tank WVO\diesel conversion) SOLD

'81 300D ~ Mama's car...my job (now my car)(but still my job) SOLD

'83 300sd ~ rescue car SOLD

2005 Ford Taurus (Mama's new car)(NOT my job!)
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  #5  
Old 11-24-2010, 01:11 AM
Registered User
 
Join Date: Nov 2010
Location: Vermont
Posts: 12
An addition

In addition to what I wrote in the original post, I forgot to mention that I made and used the DIY code reader to read and reset all my codes. None of them have reappeared, so I have no codes from the EDS, further adding to the mystery.

Please help! I'm close to having to make the reluctant decision to either replace the transducer, or go to the Merc mechanic and pay some ungodly fee to have them tell me what needs to be done.
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