Hello all,

I have a 1985 300SD with 208K miles. This past weekend I decided to inspect the turbocharger boost output, so I measure it directly after the switchover valve. On a full load run uphill I was getting 9 psi of boost. I believe that ~11psi is the factory setting. So I moved the measurement to just before the switchover valve and the same results. Next, I adjusted the wastegate 2 full turns clockwise or 2 mm. There are 1.1mm of threads from the stem tip to the adjustment nut. Re-tested boost and 9psi again? The boost is smooth, but I would have figured that i should have gained 2 psi based on some reading of how to adjust the wastegate.

Did I not adjust the wastegate enough? Or do I not have enough fuel output from the injection pump?

I was thinking of temporarly pluging the wastegate reference hose to determine if the injection pump was providing the required fueling. Any thoughts?

Additionally, I did check the fuel pressure just before the injection pump (after all filters) and it is low according to the FSM spec.:

Idle = 8 psi (should be 11psi)
3000/min = ~11 or 12 psi (should be 19 psi)

Just replaced the fuel filters too. Additionally, I pinch the return line for a second and the pump was able to build 20 psi.

I am wondering if my relief pressure valve is bad.

I am wondering if the low fuel pressure might be a cause of the low boost situation, would this significantly affect output at the injectors?

Within the past 8k miles i have performed the following repairs:
Check injection pump timing (via A-B light method)
Adjusted the valves
Adjusted the throttle linkage (huge performance difference)

I was wondering if anyone has any input. I think I am going to try plugging the wastegate hose first. Then maybe look into the fuel pressure relief valve.

Any help is appreciated.

Thanks!

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1985 300SD 200K