Help with turbo - PeachParts Mercedes-Benz Forum

bbjornson · #1 07-28-2009, 11:37 AM

I don't think my turbo is working very well...

That said, how do I diagnose it or repair/fix it to perform. I have searched the threads but can't find anything that really tackles the issue of dealing with ones turbo.

1982 w123 turbo specifically.

oldsinner111 · #2 07-28-2009, 11:52 AM

You need a boost gauge.I made one with a round tire gauge for testing.Find tee,and tee into ALDA line,run line to tire gauge.Tire gauge cut off end with valve for tires,attach hose and reduce down to line that you ran into interior(air line for aquarium works).Drive and test 3500 rpm or more in a gear.Look at gauge it holds presure on tire gauge.Now pinch line to wastegate from turbo until you get what you want -2psi.Have fun until you buy real gauge and manual boost controller.

tbomachines · #3 07-28-2009, 11:57 AM

First thing you should do is clean the banjo bolt coming out the back of your intake manifold, may make a world of difference if it is gunked up.

Jeremy5848 · #4 07-28-2009, 11:59 AM

Engine will show no boost at idle in the driveway, you must be driving the car at highway speeds. Even at 65 mph my '87 300D (and before it, my '85 300D) would show only about 5 psi boost at a steady 65 mph.

As you accelerate, the gauge should reach 13 psi and then cut off as the waste gate opens. If it does not, you could have a clogged ALDA line or overboost solenoid. There may be an unused port in your intake manifold (my '85 had one) and you can install the boost gauge there, bypassing the ALDA connections. That will separate boost/boost controller problems from ALDA problems so you know what to repair.

tbomachines · #5 07-28-2009, 01:01 PM

Quote:

Originally Posted by Jeremy5848

Engine will show no boost at idle in the driveway, you must be driving the car at highway speeds. Even at 65 mph my '87 300D (and before it, my '85 300D) would show only about 5 psi boost at a steady 65 mph.

As you accelerate, the gauge should reach 13 psi and then cut off as the waste gate opens. If it does not, you could have a clogged ALDA line or overboost solenoid. There may be an unused port in your intake manifold (my '85 had one) and you can install the boost gauge there, bypassing the ALDA connections. That will separate boost/boost controller problems from ALDA problems so you know what to repair.

Your port is the one with the Allen head plug next to the banjo?

Jeremy5848 · #6 07-28-2009, 01:27 PM

Quote:

Originally Posted by tbomachines

Your port is the one with the Allen head plug next to the banjo?

In my '85 300D-T (W123, OM617) yes. Remove the Allen head plug and replace it with a 1/8-28 NPT fitting (threads are the same as 10mm Metric). The fitting can be either a barb or a compression tubing adapter, I used the latter. The '87 300D has a similar plug in the IM next to the overboost protection switch.

If you do not get boost at that point, you have a turbo or wastegate problem (or a big hole in your IM

). If you get boost there but not at the ALDA, you have a clog somewhere between the banjo and the ALDA. Less likely is a failure of the ALDA or the overboost protection switch or solenoid. With everything else eliminated, the IP could have a problem.

Almost everyone who has posted on this forum turns out to have a clogged ALDA line. The other problems are possible but less likely. My '85 came to me with a cracked and broken line between the banjo and the overboost solenoid; my mechanic found and fixed it when he did the initial inpection after I bought the car.

Jeremy