1985 300D No power, and no pressure from boost line, only vacuum - PeachParts Mercedes-Benz Forum

ROLLGUY · #1 05-12-2012, 12:41 AM

I am working on a 1985 300D (CA emissions). The turbo does not seem to work, and the car has less power than an N/A 300D. There is vacuum only at the ALDA from the boost line. Normally there is a little vacuum at idle, and more pressure as the engine speed increases. Could the waste gate valve be stuck open? Could the trap-ox be clogged? Viewing the compressor wheel with the intake tube removed, it seems like the wheel speeds up with the engine. There is no pressure on the hose going to the waste gate actuator. Anyone have any ideas what tests I can perform to locate the problem? I have a spare trap-ox turbo, but I don't want to replace it if I don't have to. Thanks in advance......Rich

Jeremy5848 · #2 05-12-2012, 01:15 AM

Assuming the lines from the intake manifold through the over-pressure cut-off solenoid and on to the ALDA are clean and clear, you may have a dead turbo. Do you have any way of measuring boost pressure (or lack of it) in the intake manifold? If you have no boost then either the turbo is not spinning or the waste gate is stuck open (or both).

Jeremy

vstech · #3 05-12-2012, 07:01 AM

have you pulled the banjo bolt out of the intake itself to measure, or are you just checking on the small hose at the ALDA?

Brian Carlton · #4 05-12-2012, 07:25 AM

Quote:

Originally Posted by ROLLGUY

There is vacuum only at the ALDA from the boost line.

The banjo bolt in the manifold must be clean and the test for boost on the line from the banjo bolt must be done with the vehicle moving, maximum power requested, with the rpm's above 3000.

You must rig the gauge to observe it in the cabin.

ROLLGUY · #5 05-12-2012, 09:46 AM

Quote:

Originally Posted by vstech

have you pulled the banjo bolt out of the intake itself to measure, or are you just checking on the small hose at the ALDA?

On every other engine that I have checked, I could feel pressure on the banjo fitting (finger and thumb covering both sides) when the engine was revved up. On this one, I feel vacuum all the time. I can only assume the fitting in the manifold is clear. The over-boost cut off solenoid has been bypassed by someone else. I will check the waste gate valve (only 4 bolts) and see if the valve is open.

Jeremy5848 · #6 05-12-2012, 10:51 AM

Quote:

Originally Posted by ROLLGUY

On every other engine that I have checked, I could feel pressure on the banjo fitting (finger and thumb covering both sides) when the engine was revved up. On this one, I feel vacuum all the time. I can only assume the fitting in the manifold is clear. The over-boost cut off solenoid has been bypassed by someone else. I will check the waste gate valve (only 4 bolts) and see if the valve is open.

The manifold fitting in my '85 300D-T was almost completely blocked with soot. (This was before I modified the EGR valve.) It took a lot of cleaning as the entire run of line through to ALDA was crudded up. Assumption is the Mother of all Screwups. Listen to Brian.

Jeremy

ROLLGUY · #7 05-12-2012, 11:49 AM

Quote:

Originally Posted by Jeremy5848

The manifold fitting in my '85 300D-T was almost completely blocked with soot. (This was before I modified the EGR valve.) It took a lot of cleaning as the entire run of line through to ALDA was crudded up. Assumption is the Mother of all Screwups. Listen to Brian.

Jeremy

If I can feel vacuum (normally pressure) on the line when the engine is revved up, obviously the banjo bolt is not clogged. I pulled the 4 bolts holding the waste gate plate on, and the valve is closed. I am leaning toward a clogged trap-ox.