Ever drill out the boost switch??
 

Here is the situation, we all know that the boost switch that screws in the manifold gets clogged with crap and we clean them out on a regular basis. Sonce the hole in the switch is very tiny, do you think it would hurt or help if the hole in the switch was increased in diameter?

Why would you really want to. I just cleaned mine out today and it took all of 10 minutes. My boost switch is located on the fire wall. The banjo fitting is on the manifold. Cleaned out the lines, checked the switch and put it all back together. The drilled out fitting would not make any difference in what the actual pressure was. Easier to just make sure its all like its supposed to be.

Bill Rokaitis
1985 300 SD 151,430 miles

Drilled out?
 

I just had a boost deficiency problem with my SDL. The fitting was restricted but the actual blockage was where the braided hose transitioned to a short piece of hard plastic pipe which then transitioned to a rubber fitting w/screw clamp which then attached to the firewall mounted boost sensor. The very small diameter (1 mm) plastic pipe was plugged by carbon almost 8 mm in length. Cleaned out every thing and plenty of boost with the ALDA working. Looking at the problem I think that a baffle or screen on the boost fitting intake would be more useful? A larger surface area for the orifice would be harder to clog and would reduce the amount of carbon traveling through any hose?

Would simply opening up the boost fitting (drilling out) allow carbon to enter the hoses, sensor and ALDA easier?

It goes without saying that disconnecting the EGR should greatly reduce the introduction of carbon in the first place. My next project is to do this and then clean out the crossover pipe and intake manifold.

[B]Carbon what carbon[/B]
 

My 85 has no carbon problem. Am i missing something or just unusual?

No Carbon ?
 

What the heck are you burning?? Only kidding! The theory is that when oily crankcase fumes leave the valve cover through the hose near the oil fill hole they are directed into the air intake. The EGR valve near the turbo at times vents hot exhaust into the air intake as part of an emissions control scheme. Hot gas plus oil laden air combine and cook depositing carbon on the inside of the air intake areas. On my 603 motor the carbonation starts in the crossover pipe and into the intake manifold itself, You can disassemble these parts and witness this phenomena. you can also pull any of the various plugs and outlet adapters attached to the intake manifold and most likely the portion exposed to the inside of the manifold will be covered/encrusted with thick black granular carbon. If this type of carbon deposit restricts or blocks a manifold pressure port your boost system doesn't know what the manifold pressure is and in the case of turbo boost can't signal the ALDA to increase fuel proportionate to the turbo's boost. The problem is the turbo boosts the air charge but without a corresponding fuel injector boost there is no more power generated. Essentially the engine has a turbo air supply and a conventionally aspirated fuel supply = no extra power from the turbo setup. If you don't feel that extra power kick in significantly when your RPMs get in the 2500+ range you may be experiencing this problem. Conversely if all of a sudden you fail to experience the power surge your boost signal port/line might have just gotten blocked!;)

Maybe I live dangerously but I got rid of the overboost protection switch on my 300D about 8 months ago. The only protection I am running on this engine is the wastegate with a clean intake manifold :) and it runs great. I did a road test one time with it and it seems to max out at 8.5 psi so I left it alone.

Jim,
Since you got rid of the overboost switch, have you noticed any change in fuel consumption? I once considered removing the switch but a few people mentioned that it also cuts the fuel supply while deccelerating when the boost is still there. Thanks

Alex

Not too sure - I took it out pretty early in my ownership. Town/highway combined I get 25. On my longest trip (60-65 mph average - two lane) I got 29 mpg. I have noticed at work that our big turbodiesel "chip pushers" don't have stuff like this on them - they do not even run wastegates.

The overboost switch turns on at 16PSI to cut the boost, it does nothing until then and only protects your motor from self-destructing. Put it back on! There is NO advantage to leaving it off!

I agree with turbodiesel. There is no advantage to removing it. Just leave it alone. Also, some people are mixing up the switch (sensor, has one wire connected to it) with the solenoid on the firewall (switchover valve, which has hoses connected to it.) The switchover valve MUST be clean internally or it will reduce power output by not allowing full fuel enrichment at the ALDA.

I have also heard the rumor that it cuts enrichment when decelerating. I have no concrete information to support that theory, and it seems to me that the I/P should be able to compensate for that by sensing the throttle position and ignoring the ALDA position. Right?

engatwork, your boost is WAY low. Spec is, IIRC, 13-14 psi. I'd adjust your wastegate up closer to 12+ psi and I bet you'll love the added power! That is assuming the wastegate is the problem...

EGR is evil on a diesel. It does nothing but crud up the intake while decreasing power and MPG. Here's a photo of my sister's OM603 intake charge pipe, just after the EGR valve. I tried attaching it to the post, if it doesn't work, it's at this URL:

http://www.meimann.com/images/mercedes/OM603_intake/pipe_before.jpg

OK, one last time, here's the photo - I hope...

And here's a shot after I cleaned it up:

too late - call me hardheaded but that overboost protection switch ain't going back on. The simpler this car is, in my opinion, the better it is - I don't think I will ever own another car that the is newer than about 1985. In addition, I never have to worry about my intake manifold looking like the one gsxr showed in the "before" picture.
Anyway, I am going to leave the wastegate alone too - I know I am a simple minded redneck BUT in my narrow minded way of thinking the less stress (low boost and early shifting tranny) the longer this baby will last. Anyway, I have two other MB's to drive if this one does break. If I want to go faster than about 65 mph I will take the E320 and if I want to go slower I will take the 240D.
I have on my "to do" list to pull the cylinder head on the 300D because of the pressure in the cooling system 18 hours after I shut it down but as busy as I have been lately that is not too high on the priority list right now (Gatornationals - national drag racing event coming up in Gainesville, Fla this weekend). My friend with the supergas car is already there and Blake (8) and I are planning on taking the Honda CRV down this year where we can strap the bicycles on the top.