You cannot put sufficient load on the engine sitting in your driveway. You cannot get a proper read on the boost without taking the vehicle out on the road. There is no alternative.

I connect my gauge and route it through the driver's window on both of these. It's become second nature. The connections and T's live with the gauge.

Thanks Brian for your help I did not no that you needed the fuel inrichment along with the boost, so if I have the 12-15 pressure at 4000 rpm at the line that goes to alda then the problem is with the adjustment of alda or the alda itself?

Correct.

But, you are not going to get 12-15 psi on a 20 year old engine. Typical boost will be on the low side, maybe 8-10. You can dial it up by adjusting the wastegate spring which gets soft with age.

My 617 runs at about 9.5. I'm not dialing it up until I fix the head gasket.

Brian one last question how do yo tell if the wastegate is bad or not when I blow through the line that feeds the wastegate air comes out on the bottom of the wastegate.

That line should be holding pressure. If it doesn't you need to determine if the diaphragm in the wastegate is bad. If it is, the wastegate won't open and allow the boost to be limited. The hose could also be cracked from heat.

Please, take it for a drive, with the boost gauge connected as I previously explained. Report back on the boost levels. If you get boost above 14 psi, then the wastegate diaphragm is not working at all.

However, at 15 psi, the overboost protection kicks in and all fuel enrichment is stopped, thereby cutting exhaust temps. immediately.

you will not see much at all with the car stationary. You have to load the engine and make it pull a grade or go down the road to see any significant boost pressure. What model Benz are we taling about here BTW, or did I miss that somewhere???

I do get 5 psi at 4k rpm when the car is stationary, but still, definitly not an accurate way at all of getting your actual pressure.

anyone know the stock pressure for a 603? same as a 617, about 13psi?
whats a decent number for one with 234k on it?

The 603.961 is rated at 11.25-14.25 psi.

I would think anything over 10 psi would be acceptable.

You might be able to adjust the wastegate to get it back toward the middle of the spec.

Yes...The Wastegate Valve Stem is hollow and there is a hole drilled through the side of the stem about midway down its length. This allows pressurized air acting on the diaphragm piston to 'bleed' down through the stem and cool the valve.

This bleed function also prevents 100% of the boost pressure from acting on the diaphragm.

The opening in the side of the valve stem is exposed below the diaphragm piston and there is a rectangular hole in the Wastegate Housing that allows this pressure to vent to the atmosphere.

Here is a post on the proper adjustment procedure for the wastegate. You can visually inspect the diaphragm and valve movement when you have the cover removed.

I hope you find this information helpful...Bert

Wastegate Adjustment

Dieleldiehard ask a very important question. What model and year car are we talking about? My 91 300D has to see vacuum on the wastgate to produce boost. If the line is disconnected or pluged you get no boost. On others if the diafram is bad or the line is disconnected you will get overboost.

pmckechnie raised more points than I imagined
What about if the trap oxidizer is still in place? That is a bad thing when it comes to Turbo problems, esp the '87 300D and SDL :rolleyes:
The year and model are sometimes crucial towards understanding a problem in its entirety.
I am still convinced it may be a wastegate flapper stuck open.

Its a 84 300 Turbo Diesel with 292,000 mi. and clean as a whistle.

Bert,

Since many of the older vehicles have boost pressure that is below spec, is it possible that this hole becomes clogged over time and allows close to 100% boost pressure on the diaphragm?

This would cause premature opening of the valve and result in decreased maximum boost pressure.

Your thoughts on this???

If the shaft has a hole down the middle of it where does this excess air go. The reason I ask is when I blow through the hose that goes to the wastegate
I feel air on the bottom of wastegate is this normal?

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