What Could I have Done to Creat This Problem??

[steve kane]

Well as regular readers may be aware last week I replaced the O Rings on our C250D Fuel Lines, this involved me in removing the Washer Bottle and Inlet Manifold as well as the Fuel Lift Pump and Fuel Cut Off Valve, clearly much of the work was carried out with my arms/hands stuck down the near side of the engine. Immediately after this work was completed, on the test drive to make sure everything was okay, we noticed that the changes on the Auto Box were very harsh indeed, each change coming in with a bit of a wallop. I looked round but could not see anything amiss except for the Stray Vac Tube I found coming from the top of the Vacuum Control Valve(up by the ECU and Throttle Mechanism) which was open ended and not connected to anything, I assumed this was the problem but I have today learned from another forum member that on his C250D the Vac Tube on his car is also lying loose and his changes are just fine! Well I now really don't know what to look for, does anyone have any idea of what I could have disturbed/knocked off in the near side area of the engine bay that would result in instant very harsh changes? all idea and suggestions welcomed,
Steve.

 

[ba9rn]

It is supposed to ease off the throttle during changes, and a harsh change does sound like it's not happening. Could be a loose connection somewhere - Malcolm?

 

[Blobcat]

It is supposed to ease off the throttle during changes, and a harsh change does sound like it's not happening. Could be a loose connection somewhere - Malcolm?

I don't think Malcolm having a loose connection is the problem but I'm sure he could give some advice. :grin:

 

[ba9rn]

hmmm.

 

[television]

It is supposed to ease off the throttle during changes, and a harsh change does sound like it's not happening. Could be a loose connection somewhere - Malcolm?

The vacuam system should ideally all be intact, like a vacuam cleaner any hole in the pipe or bag reduces the suction in the whole system, the same goes for the vacuam system on cars below in the link you have all of the connections


http://www.detali.ru/cat/oem_mb2.as...GM=717.417&CT=M&cat=19S&SID=14&SGR=123&SGN=07

malcolm

 

[Hibbo]

Alright mate,

Right then, assuming your car has a vacuum controlled box (as opposed to electronic) it should be pretty similar to mine (vacuum wise).

There should be a proportioning valve on the side of the injection pump, this will have 4 vac pipes attached to it, on the top: one on its own and two on a tee. then one on its side.

On my w123 it's like that anyway! There will at least be a vac supply, a proportioned vac to the box, (these two are on the top) and a vac vent (on the side, goes through the bulkhead on mine)

If these are not on (or on the wrong way) it will give very harsh changes.

The proportioning valve's job is to mimic the manifold vacuum you would get on a petrol engine (foot off the pedal - high vacuum / foot to the floor - little vacuum), it is fed with a large vacuum from the main vac line from the vac pump to brake servo, and it 'dumps' vacuum to atmosphere the more you put your foot down. If there is a leak/pipe off, there is no vacuum presented to the box, so it 'thinks' you have got your foot to the floor and really bangs the changes in.

This is definately a case of no vacuum reaching the gearbox - you just need to find why!

Good luck my son...

 

[steve kane]

Many thanks, everyone, esp Hibbo and TV for the link to the Vac System Diagram, my set up is I think similar to the diagram shown on the link and the stray line is numbered 155 and comes off the top of the Vacuum Control Valve, it says it is "Ventilation, Electric Switch Over Valve" but I'm not sure I have been able to identify the Elect Sw/Over Valve yet, I will have another go tomorrow. The set up on our car differs from most it seems in that the Vac Control Valve is located up by the windscreen with the ECU rather than on the side of the Injection Pump which I think is the more usual place(?) The comments about just having an open pipe are I think perfectly reasonable, it seems a very odd thing to just have a loose pipe, why bother with the pipe at all? just have the little rubber elbow! but well see. l will keep you all posted on my progress. BTW TV where did that page come from that you sent through? its not on the other link on this site though clearly its the same manual, thanks once again to you all for your help,
Steve.

 

[television]

http://www.detali.ru/cat/oem_mb0.asp?TP=1

You have to know the way around to get the best from the site.

for your problems, go to the engine section on the right.
next inlet manifolds
you now have the choice of all the vacuam systems.

its all sections with sub sections.

Malcolm

 

[steve kane]

Many thanks Malcolm, I have had another look at the diagrams this morning then went and removed the various covers, washer bottle etc on the car and set to and traced through all the Vac tubes, I found that "pesky little 158" the Vac tube that is described as "Line from Electric Change Over Valve to Transmission" is disconnected at the gearbox end, gentle teasing brought the pipe end into view, this vac pipe runs by the Injection Pump and I guess I must have dislodged it whilst ferreting away at my fuel lines. Normally things like this, pushed into rubber connecters, "stick" themselves in and take a bit of a firm tug to pull them out so I'm hoping that when I get under there and snugly reconnect it the gearchangeing might be better than before,,I will keep you posted, I'm still looking for a good home for 155 (Vac Tube Ventilation, Electric Switch Over Valve) but that can wait for another day, thanks once again,
Steve.

 

[Hibbo]

Nice one mate, I'm pretty sure that'll sort your woes.

As for the point of having a vent line, all I can think of is that as the vac vent line is always sucking, having it out the way (behind the bulkhead for example) prevents any crap getting sucked in to the vacuum system.

 

[steve kane]

Well so far I have not been able to refit the Vac tube, nothing sinister just the wet ground and the discovery that the engine and gearbox is covered over with an undertray which makes getting to the connectors more difficult, I may have to nip it up the road to the local garage and see if he will pop it up onto his ramp, looking at the diagrams for the Vac System it appears that the connecters are just bits of rubber tube, so replacements if required should not be a problem. Its at times like these that I wish I had a nice big garage, with a pit!! As to the vent line, well Hibbo I think you could be right, I certainly cannot find anywhere for it to connect to and its disconnected on another members car which is running just fine so I suppose that's what it is supposed to be like, it just seems odd that Mercedes would have just left it like this?
Steve.

 

[steve kane]

Well its fixed at last, the Vacuum tube running down to the near side of the gearbox is reconnected and the changes are back to there bit jumpy 1st change then fine after that, however for anyone thinking about changing this rubber connecters its worth bearing in mind that even after removing the undertray there was very little room between the gearbox and the side of the car in which to get your fingers, even up on a ramp with a lead lamp we had quite a job getting the plastic vac tube back into the rubber connector and only managed it after gripping the tube gently with a pair of long nosed mole grips, definitely not the sort of job to try and do lying in the road with the rain running down your neck!! I popped along to our local tyre & exhaust fitting shop and the chap agreed to pop it up onto the ramp and whip the undertray off for me, something I thought they would be used to doing, I then assisted the lad to do the job and all for the price of a couple of pints,
thanks to everyone for there assistance and helpful suggestions,
Steve.

 

[television]

Hello Steve so pleased that you are back to normal, though you do not have an electric lock up box, the weather is a bit on the cold side for super smooth changes, let us know what its like on a run when your mind has stoped focusing on harsh changes.

Good luck. Malcolm