EGR System affect transmission shift? - PeachParts Mercedes-Benz Forum

willrev · #1 12-11-2004, 10:41 AM

I am looking on page 134 of the Haynes repair manual. It has a vehicle emission control diagram. It consists of the Fuel Injection pump, the egr valve, vacuum pump, switchover valve on tome of the valve cover, vacuum control valve on injection pump, orifice, damper, central vacuum connector, and thermo valve 17degrees c.

The switchover valve on top of the valve cover has a cam arm that opens and closes the valve. If this valve has a worn out cam arm - can this affect transmission shifting?

The other recent post about EGR has everyone debating over whether or not to disable the EGR and how it affects engine temperature and gunk in the intake. I have scanned this diagram and would include it in this post but am not sure if this post will allow a JPEG image to be included. I could not seem to get it to work. I don't have a website where I can post the image, but could email it. It is on page 134 of the Haynes manual. Wish I knew of a better manual. This one is very very vague on vacuum system.

willrev@earthlink.net

wolf_walker · #2 12-11-2004, 11:44 AM

I have the grey factory manuals for w123, engine vac stuff is the same. I'll show it to you. We have GOT to get together some weekend.

On the vac system. I've said for a long while that no you don't need EGR or the two white switchover valves on the valve cover. I've decided I was wrong about the later, in a way. One of those two valves I believe is for EGR control, the other seems to give a very high vacuum at closed throttle to ensure you don't feel downshifts(an example of what happens when you have hardish shifting and do not have this feature is my car, which about half the time you can feel downshifts). Trouble is the darn valves are kinda pricy, about $30 a piece(and no there are none at the salvage yard). I believe you can live without them if things are in good shape otherwise with your trans, but if your like me and have to have line pressure a little above spec on the trans, and overall low vacuum to keep flairing down on a perticular shift or whatever, you end up with harsh downshifts. That's my considered opinion anyway.

Everything effects everything else in these cars. Remember that. Say you improve something, adjust the ALDA or whatever, your makeing more power, so you tend to be less on the throttle overall driving around, and therefore your trans is shifting softer than it was for a given acceleration. This can be bad if your makeing more power at less throttle and you don't adjust things accordingly. Complicated, it is. I still want a stick...

psfred · #3 12-11-2004, 11:55 AM

I believe that the EGR and tranny shift control are operated off the same vac line on that car, so yes, a failure in the EGR system can affect shift feel and timing.

You can replace the "finger" in the control valve, I believe, but if the valve itself it worn out, you must replace it.

Transmission modulator line should have 15-17" vac with 'throttle" closed, I belive, dropping to about 12 a soon as you touch the pedal. This keeps tranny in 2nd until you touch the throttle, when it should immediately downshift to first. Vac should then drop to zero at full throttle.

What happens with these is that the range from zero to full pedal position shrinks as it wears, causing either mushy shifts or harsh, late ones depending on where you set the "zero" position. Eventual cure is to replace the vac regulator.

You should also verify the absence of vacuum leaks in the associated tubing and make sure you have a good main vac pump and modulator. Also check the orifice in the fitting in the main vac line, they tend to plug. Clean only, do not drill it out!

Peter

phantoms · #4 12-11-2004, 12:06 PM

Quote:

Originally Posted by willrev

Wish I knew of a better manual. This one is very very vague on vacuum system.

I posted several vacuum diagrams a while back.

Vacuum Diagrams

willrev · #5 12-13-2004, 06:24 AM

Quote:

Originally Posted by psfred

I believe that the EGR and tranny shift control are operated off the same vac line on that car, so yes, a failure in the EGR system can affect shift feel and timing.

You can replace the "finger" in the control valve, I believe, but if the valve itself it worn out, you must replace it.

Transmission modulator line should have 15-17" vac with 'throttle" closed, I belive, dropping to about 12 a soon as you touch the pedal. This keeps tranny in 2nd until you touch the throttle, when it should immediately downshift to first. Vac should then drop to zero at full throttle.

What happens with these is that the range from zero to full pedal position shrinks as it wears, causing either mushy shifts or harsh, late ones depending on where you set the "zero" position. Eventual cure is to replace the vac regulator.

You should also verify the absence of vacuum leaks in the associated tubing and make sure you have a good main vac pump and modulator. Also check the orifice in the fitting in the main vac line, they tend to plug. Clean only, do not drill it out!

Peter

Peter - I have cleaned the orifice in the main vac line. I have not played with my ALDA at all. I have confirmed the vacuum valve located on the valve cover is worn out. Is this valve the regulator you are referring to when you say, "eventual cure is to replace the vac regulator."???

I am replacing the valve cover vacuum valve with a new one - not parts yard. This is the only vac leak I could locate.

rg2098 · #6 12-13-2004, 06:49 AM

Quote:

Originally Posted by willrev

Peter - ... I have confirmed the vacuum valve located on the valve cover is worn out. Is this valve the regulator you are referring to when you say, "eventual cure is to replace the vac regulator."???

No, The valve that loses its range over time sits on the back of the IP. Its whiteish yellowish with a vac line on the top and side and a connection to the throttle linkage. Alot of people mistake it for the shutoff valve.

Pete Burton · #7 12-13-2004, 08:33 AM

Quote:

Originally Posted by psfred

What happens with these is that the range from zero to full pedal position shrinks as it wears, causing either mushy shifts or harsh, late ones depending on where you set the "zero" position. Eventual cure is to replace the vac regulator.

Peter

Another nice nugget of information! Explains a lot, actually

tomm9298 · #8 12-13-2004, 09:48 AM

I got both valve arms from Phil, I can't remmber the price but it was VERY cheap. A few dollars each. Call Phil !!!!

deeph8 · #9 12-13-2004, 05:59 PM

Yesterday, while I was in the process of replacing various worn vacuum hoses under the dash, I found an open-ended black hose just under the steering wheel. I could not figure out what it attached to, so I plugged it with a 1/8" cap. Today, I was looking at the vaccum/egr diagram posted here and I saw that there is supposed to be a black hose venting to the passenger compartment. Why would this be? I suppose I need to go back under there and remove the cap. It just doesn't make sense to me. Also, the cap does not seem to have made any difference.

http://www.ultrahot.com/vacuum/fuel_egr_240d_auto.jpg

Pete Burton · #10 12-13-2004, 08:20 PM

That tube pulls air from the passenger compartment only because it is probably cleaner and drier than that in the engine compartment. Air travels down that tube and through the vacuum control valve on the IP. (hopefully) very little at no throttle to a lot during full throttle. As the trhottle is increased, more and more air is allowed through the valve, causing less vacuum in the line to the transmission modulator, which should mean less control pressure as the throttle is increased.

psfred · #11 12-13-2004, 08:22 PM

The vent is under the dash to keep dirt out of the vac pump. Check the line for leaks and for a damaged connector to the valve.

Some of the vac control valves are on the IP, some are on the valve cover, there will be only one on any given car.

If the valve itself, not the operating "finger" is shot, there is no repair, and a new one should restore proper shifting. If not, check and adjust or replace the vacuum modulator. It must hold vac and operate properly. They are not expensive.

Peter

phantoms · #12 12-13-2004, 10:00 PM

Where that vent line exits the firewall to the engine compartment, there is also usually a small filter in it. This further helps keep the vacuum supply clean. Take the filter loose and make sure there is no restriction through it. If not, reinstall it. It's there for your protection.

deeph8 · #13 12-13-2004, 11:37 PM

what does the filter look like? I didn't see anything there at all, just a hose with an open end.

willrev · #14 12-14-2004, 06:53 AM

If you go to transmission.articles.mbz.org/adjust/ you will read that the vacuum switchover valves on top of the valve cover definitely affect shift characteristics. There are levers on two vacuum valves and if they are worn they will affect shift. Part #123-304-0220.

If these are not working then you will not get a correct vacuum reading on the regulating valve on the injection pump.

Replacing these as we speak.

WannaWagon · #15 01-11-2005, 07:38 PM

I'm chiming in really late here, but just wanted to say that today I plugged the vacuum line to my EGR valve and noticed an immediate reduction in shift harshness. The 1-2 shift is now buttery smooth, literally, where I used to have to warn passengers not to take a sip from their travel mug or whatever until that shift was through! Kinda amazing change. Could it be the EGR valve or the line to it were leaking vacuum, thereby robbing vacuum from tranny circuit and causing those harsh shifts?

Anyway, I can't believe I didn't plug the EGR line a long time ago. My wagon behaves much more like a 'normal' car now, with a smoother idle, more power, and the nicer shifts. I'll be eager to see if it improves mpg at all.