Back under the hood today, (my wife is getting real excited about all the time spent there). I ran some more pressure tests on the overboost valve (waste gate) and notices some air leakage from carbon build up on the valve and valve seat. Dismantled the valve again, cleaned the valve stem good with WD-40, and slid the valve out. I clean as much carbon out as possible with a homemade wooden chisel, than lapped the valve in tith 2 step valve grinding compound. Put eveything back together and test drove the car.

No good, still very low on power and could only pull 5 PSI of boost starting at 3300 RPM in 3rd. Once again isolated the ALDA circuit, and artifically pressurized the ALDA. Car than ran much better with as little as 3 PSI to the ALDA. With 5-10 PSI on ALDA, turbo started boosting at 2200-2300 RPM, with 10 PSI of boost. Appears the work on the waste gate did some good as far as increasing boost pressure, but the ALDA is still not enriching the fuel properly on its own, just relying on the turbo boost. Seems it just can't react well enough to start the enrichment/boost/more enrichment/more boost cyle. I hate to have to mess with the ALDA screw, but this now appears to be the the only course of action left. I'll try adjusting this tomorrow.

Don't know much if anything about start of injection timing, but I'm wondering if this could be part of the issue. I'll research threads on this.

PS: If you're looking for 0-30 PSI pressure guages for testing purposes, I bought two Harvard brand guages out of the pool supply dept at a local hardware store for only $4.99 each, and they test out to be pretty accurate. I also saw 0-30 PSI acetyline (sp??) guages for $14.
Gene

Back under the hood today, (my wife is getting real excited about all the time spent there). I ran some more pressure tests on the overboost valve (waste gate) and noticed some air leakage from carbon build up on the valve and valve seat. Dismantled the valve again, cleaned the valve stem good with WD-40, and slid the valve out. I clean as much carbon out as possible with a homemade wooden chisel, than lapped the valve in with 2 step valve grinding compound. Put eveything back together and test drove the car.

No good, still very low on power and could only pull 5 PSI of boost starting at 3300 RPM in 3rd. Once again isolated the ALDA circuit, and artifically pressurized the ALDA. Car than ran much better with as little as 3 PSI to the ALDA. With 5-10 PSI on ALDA, turbo started boosting at 2200-2300 RPM, with 10 PSI of boost. Appears the work on the waste gate did some good as far as increasing boost pressure, but the ALDA is still not enriching the fuel properly on its own, just relying on the turbo boost. Seems it just can't react well enough to start the enrichment/boost/more enrichment/more boost cyle. I hate to have to mess with the ALDA screw, but this now appears to be the the only course of action left. I'll try adjusting this tomorrow.

Don't know much if anything about start of injection timing, but I'm wondering if this could be part of the issue. I'll research threads on this.

PS: If you're looking for 0-30 PSI pressure guages for testing purposes, I bought two Harvard brand guages out of the pool supply dept at a local hardware store for only $4.99 each, and they test out to be pretty accurate. I also saw 0-30 PSI acetyline (sp??) guages for $14.
Gene

300Dguy,

Thanks for the explanation of how the overboost cylinder and wastegate work.

U pressurized the ALDA separately and it seemed to improve the performance, right? So that tells me that the ALDA is working OK. Have you measured the pressure at the ALDA created by the manifold pressure, even if the manifold pressure is lower than it should be? Is the pressure at the ALDA the same as the pressure in the intake manifold?

Not having enough boost pressure sounds like the root of your problem. I think U should try getting the correct boost pressure before U change the ALDA setting.

Just my 1.5 cents.

P E H

Adjusting the ALDA won't solve the problem.

Injection timing might be an issue, but, it can't misadjust itself overnight. The symptoms occurred overnight........a change in timing is a gradual event.

I reviewed all the posts on the thread and I come to the issue of the exhaust. You modified something in the exhaust prior to the event. Whether the exhaust affected the situation is therefore questionable.

Therefore, I might offer the suggestion to drop the downpipe.........support it with some jury rigged affair.......and take if for a drive. If the problem remains, it would rule out the exhaust as the culprit.

Furthermore, did you ever have a chance to check the turbo for ease of rotation and for both axial and radial play? If the turbo developed a problem.....it could have a sudden onset........and the performance of the vehicle would suffer in similar manner to your symptoms.

Brian,
You might be on to something about the exhaust. Would this have made any difference...I recently (1 week before this problem started) swapped the entire exhaust system from the down manifold pipe to the tip of the tail pipe with a unit off a 1983 non Calif. parts car I have. My last muffler was developing a hole in the bottom and the donor car had a perfect Mercedes stock unit. The only difference I could see was the donor car's system was sleeved between the two mufflers, and the end muffler seemed much lighter than my original. I also had a much hollower sound when I tapped them both. I figured mine was just getting plugged up. However, I wondering if Calif. cars require a special end muffler that's designed to provide more back pressure. I can check with the dealer parts guy on Monday. I may also try your suggestion of disconnecting it all together.

I did check the turbine for roatation and end play through the air intake end of the unit. It seem to spin ok and I could not detect any end play. It spun like the bearings or bushings were snug, but it did not continue spinning freely on its own after I removed my finger. Having never done this before,????

To the question posted above about boost pressure at the ALDA, I can only get it there if I artifically enrich the ALDA and I can't do this using isolated circuits. The turbo won't boost properly connected directly to the ALDA.

Brian, your point is well taken about the ALDA probably not being the issue due to the rather onset of this problem, but could age alone possible have finally take its toll? If I loosen the screw/shaft, perhaps the very slight initial boost with more easily trigger the ALDA and the boost increase cycle will work??

Gene

If it were my car, I would certainly try adjusting the ALDA. The adjustment screw controls the spring tension, which opposes boost pressure. Similar concept to the boost control valve. Reducing the spring tension should make the ALDA more responsive to a given level of boost pressure.

Thought it wouldn't hurt to mess with the ALDA screw. I indexed original position, then backed it CCW 1/2 turn. Warmed car up and went for ride. Better, but not back to original. Faster off the line, turbo begins to build pressure a little faster (3,000 rpm), max boost measured at ALDA was 5 PSI. Then backed screw out add'l 1/2 turn. Car even faster off the line, turbo starts to build pressure at 2300, but still max's at 5 PSI. (Achieved 10 PSI previously with artifically pressurizing ALDA at 7-10 PSI) ??????
I'm hesitant to adjust the ALDA any further, car is running much closer to previous performance. Will consider exhaust disconnect if it ever stops raining!!!!

I haven't ruled out a leaking EGR valve. I can hear it funtioning with my might vac, but how can I tell if the valve is seating correctly or opening when it shouldn't??? I pull the vacuum line and take it for another ride, but this won't eliminate a possible bad seat of the valve.

Can anyone tell me if when checking the turb (engine cold), should the impeller spin very freely and continue to spin after a finger flick? Mine feels ok, but is far from loose.
Gene

Mine spins freely but stops spinning almost immediately. The bearings are a floating type, so they are not at their optimum performance unless the oil is under pressure.

Are you 100% sure that you don't have an obstruction or leak somewhere between the intake manifold, the switchover valve and the ALDA?

300D,

Even if U get the ALDA to add more fuel by adjusting it, U still won't get maximum performance if the boost pressure is only 5 PSI. And U might decrease your fuel mileage because the mixturer will be too rich.

The boost pressure should come up first, then the ALDA adds more fuel. Of course it happens so fast there is no noticable lag.

Since the change happened when U changed the exhaust system, some how that is the root of your problem. I have almost always found that when something doesn't work right after I fixed something, something else done in the fix (probably accidentally) is the problem.

Like the guy that changed his oil filter and the engine wouldn't shut off. He accidentally pulled off the shut off vacuum line. The accident was pulling off the vacuum but the fix was changing the oil filter.

P E H

As I figured, the ALDA is not the root cause of the problem and adjusting it only serves to mask the original symptoms.

I need to understand how you measured boost when you artificially pumped up the ALDA with the Mityvac. You mention that you achieved 10 psi boost when you artificially pressurized the ALDA. Can you confirm that the 10 psi boost measurement was definitely a manifold pressure and NOT a result of pressurizing it with the Mityvac. It's common to T into the ALDA line and, if you make an error, the Mityvac will pressurize your measuring gauge as well.

If the test was done properly, you have ruled out the wastegate as the root cause of the problem.

I agree with the recommendation to check all the lines from the manifold to the ALDA again. Connect a hose to the overboost valve on the firewall (remove the line from the manifold) and pressurize this hose to 15 psi. See if the line holds pressure to the overboost valve and onto the ALDA.

Double check the line to the manifold and be sure that it has no cracks. The old lines are very hard and brittle and it doesn't take much to fracture them. It's not easy to pressurize this line under a test procedure because of the banjo fitting on the manifold end. If in any doubt, replace this line. It comes with the banjo fitting attached and the cost is not too great.

I met the enemy and it's me!! As per above I got the car running pretty good. My son-in-law drove the car today and remarked the accelerator pedal seems pretty stiff. However, he is 6'+, 227 lbs and I noticed the car ran even stronger with him driving it, especially when he stomped it. We got home and I decided to take another look at the accelerator linkage. I had done this previously, but only moving things while under the hood. When pushed down on the pedal with only moderate pressure, the rod to the IP was not traveling all the way down??? I then looked at the accelerator pedal and noticed the think rubber pedal cover had come off, and was meticously wedged behind the pedal, hence it would trip the kick down switch, but was not allowing the linkage to work properly. (my wife is shorter, insists on driving with the seat on the wheel, and ends up bunching up the floor mat that caused this to happen)

I removed the villian, took the car out for another test drive and wow, does it move out nice. Excellent acceleration off the line, with still a noticable boost kick at between 2k-2.5K rpm. Better acceleration and more voluntary boost on hills. Full boost in "S" 3rd, still seems to max at about 7 PSI, however I havn't yet taken it out on the interstate and really pushed it in 4th.

Definitely, I am somewhat embarrased to say the least, however, with the cleanup on the waste gate, banjo fitting etc. the car is even stronger than before, and I learned a hell of lot of info about how things are supposed to work, as well as many other members I hope.

The ALDA screw is still out 1 full turn, and this is definitely enhancing start up acceleration. However, I do not detect a stronger diesel odor associated with other Benz's I have seen with modified ALDA settings. I tanked up and will check my MPG. If it has dropped, I'll start inching the ALDA setting back to its original position. Right now I just want to enjoy driving this car again.

As to the quesion above as to how I was checking turbo boost and artificially pressurizing the ALDA. I ran the banjo outfeed line from the rear of the intake manifold directly to a 0-30 PSI guage. I than tapped into the line coming out of the overboost/switch over valve and hooked up my mighty vac and another 0-30 PSI guage. I would then pump some pressure into the ALDA line and note the pressure on the second pressure guage. BTW, once I stopped pumping pressure into the line, it would hold steady per the second guage.

Brian, you win the prize insisting it must be something simple since the change occurred overnight.

I do have one last question. I tried to attach pictures but I give up trying to shink the file enough to attach them. There is a device on the front/top of my turbo labeled "By-pass valve" on the vacuum diagram label. There is approx 2' of thin black rubber vacuum line attached to a blue/red striped clear vacuum line that runs over to another device mounted on the drivers side fender well labeled " Electric-switch-over valve". This is not the Overboost waste gate valve, and it is attached to the turbo right near the connection to the intake manifold. I tested this "By-passs" valve and it bleeds down under both pressure and vacuum. Don't know if there is a ruptured diaphram in it or just a small orfice. Can anyone tell me what these components are supposed to do? Perhaps this is only on Calif turbos??
Thanks again everyone,
Gene
PS: If anyone wants photos of these two items I can probably e-mail them directly to you.