The part at the lower left below the wastegate actuator, and what does it do. Problem is the car only makes 4 psi boost and while the waste gate is fine I'm not sure what this other part is for or how to test it.

My guess it that it's your air recirculation valve? My car has a different turbo than yours. I've got a kkk-k24 turbo. I think yours is a Garrett TB03.

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2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
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'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
'87 300D Turbodiesel - sold
'82 300D Turbodiesel - sold

The thing held by 3 bolts to the turbo is the air recirculation valve as SW said. With a vacuum signal, a piston moves back to open a path between the compressor outlet and inlet. Most of its reason for being is to warm up the trap oxidizer.

Sixto
95 S420
87 300SDL

If this air recirculation valve is defective would it prevent the turbo from making more than 4 psi boost which is the current problem? How is it tested?

I think you'll need to hook up a vacuum pump to it and see if it holds vacuum. I doubt the ARV is the problem because the valve should be closed until vacuum is applied to open it. I'm pretty much having the same trouble as you with my car. I can get 12psi boost but it takes a looooong time to get there. I was told its a restricted fuel supply and that the ALDA should be adjusted.

__________________
2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
-------------------------------------
'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
'87 300D Turbodiesel - sold
'82 300D Turbodiesel - sold

Could be a wastegate flap stuck open or an ARV valve stuck open. The ARV in my SDL worked well but the plunger that covers port in the compressor outlet was deformed allowing cosiderable boost leak.

Sixto
95 S420
87 300SDL

That's the air recirc valve. Remove and plug the vac line and see if it gets proper boost. If so, leave it plugged or fix the system, if not, you have a stuck valve (remove to check) or a poopy turbo (time for new bearings).

Check to make sure the wastegage actuator rod is moving freely -- I've seen them with the link missing. That keeps the wastegate open all the time (it's held closed by the spring in the actuator). Boost gets much better with it closed...

You will probably want to check the turbo itself, too. Remove the air intake hose from the front ENGINE OFF!!!! and spin the compressor wheel by hand. It must turn freely with only a little friction. Some small radial play is normal (floating bearings), but axial play or more than barely detectable side to side play means new bearings. If it binds at all in rotation, the bearings are shot and it won't come up to speed.

Do NOT touch the turbo wheel with the engine on, it will eat your fingers.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I had a similar problem with my '87 300D last year. Finally traced to excessive exhaust back pressure due to a clogged CAT. You can check exhaust back pressure at the threaded port at the top front of the exhaust manifold.

Wray

Wray,

By "CAT" do you mean the replacement for the trap oxidizer? I always assumed that the trap ox replacement/modification was a hollow piece of tubing. Does it actually have a core similar to a catalytic converter?

__________________
2001 Dodge Ram 2500 Cummins Turbo Diesel - 4x4, auto, 3.54 gears, long bed
-------------------------------------
'92 300D 2.5 Turbodiesel - sold
'83 300D Turbodiesel - 4 speed manual/2.88 diff - sold
'87 300D Turbodiesel - sold
'82 300D Turbodiesel - sold

Trap oxidizers were replaced by a pipe between the exhaust manifold and turbo, and an oxidizer catalys device downtream of the turbo.

Sixto
95 S420
87 300SDL