Im hoping for a little help regarding my recently acquired 83 300td boost pressure. I've owned a 79 300sd for 7 years and performs fantastic so I'm trying to get the TD up to spec and am a bit stumped about my boost readings.

The overboost switch is by passed and I put a T in the line with a hose going to a guage in the cabin. Boost is maxing out at 9psi so I figured a wastegate adjustment was in my future. However I decided to pinch the wastegate hose and check my max boost and it still only went to 9, I expected much higher. I figure I must be doing something wrong either with my plumbing or my interpretation.
To install the boost guage I used refrigerator water line and white compression fittings designed for the same purpose. They are rated for 60psi so I doubt they are leaking but I suppose it's possible. For a guage I'm using a winters psi guage from Amazon that goes to 15psi.
I took of the airfield housing and turbo elbow and the turbine appears to have no play and spins freely. The boost seems to engage at the right moment and does its job. Overall the engine runs well I'm just trying to get performance to get close to my 79.
Thanks in advance for any insight and advice

Exhaust issues like it is full of soot and cannot breathe OR intake dirty? Remove the wastegate hose entirely and plug the hole, then recheck. Mine would go to 15psi easily, without an exhaust watch out it would start climbing fast to 20+.

Is the wastegate vacuum or boost actuated?

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UK spec Mercedes W210 E300 Turbodiesel wagon - OM606.962 with 722.6 transmission - rust free!

The wastegate is boost activated. They're tricky to adjust due to rusty bolts and a tight squeeze in there.

9psi from the factory sounds about right, but it should definitely be capable of 12 easily.

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No merc at the moment

Mine would only produce about 9-9.5 so I blocked the waste gate hose to verify that it wasn't lack of fueling creating the low boost. It went to 15 easily, so I added a cheap eBay universal adjustable boost controller and set it to max at 11.5. It's worked really well thus far. Just didn't t want to open up the turbo to adjust the spring for the reasons previously stated.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Thanks all, clacker I replaced the air filter so I think the intake is fine. Not sure how to check build up in the exhaust but I'll look into it. I actually had to do a bit of research to figure out how exhaust would affect boost but I think I understand now so thanks for nudging me in a new direction. I'll try and remove the hose next chance I get and report back.

Poking around my exhaust I found a section that was patched before my ownership on the vertical pipe Comming down beneath the turbo. The patch seems solid but there is a little exhaust spot on the edges indicating a small leak. Could this explain a loss of boost pressure?

No, that's after the turbo. You could remove the pipe entirely and it would make no difference.

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Exhaust makes a huge difference with boost pressures when not running a waste gate! My car runs 15psi with a factory exhaust, when the downpipe broke boost was hitting 25+ (the limit of the gage). If you have low boost a restrictive exhaust can be the problem, it can be piled full of soot or internal baffles can be broken, a leak will not be an issue no, but restrictions inside can be.

Thanks to all for the help. I still haven't had a chance to completely disengage the wastegate but I'm curious if anyone can tell me how to check for a restrictive exhaust.
Cheers

Run the car with the downpipe off the turbo, watch to see if the boost is higher.

The wastegate could be sticking open. 9 PSI is not abnormal for a stock setup, though. Blocking the wastegate should get you into the 15PSI range.

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1991 F250 super-cab 7.3 IDI. (rebuilt by me) Banks Sidewinder turbo, hydroboost brakes, new IP and injectors.
2003 S430 - 107K
1983 300SD - Tanoshii - mostly restored ~400K+.
1983 300SD - Good interior. Engine finally tamed ~250K.
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