I am newish to a 83'300sd and have read many posts on wastegate adjustment etc. I took the whole turbo/exhaust manifold off because I could not find the spring/slinky on the wastegate cover (oh well...) made a thin wrench (by way of bench grinder) found that I could turn the threads all the way in until the adj.nut bottomed out...(4 threads) put it all back on and it worked! increased the boost! but, I was hoping for more...(being human) added a boost guage and went from around 8psi-10psi...I did notice an increase in power but I have read that it should go higher if you adjust the wastegate ? so my question is ; is my wastegate leaking? or is the turbo getting tired? (I guess that's two ?s) I haven't seen much to believe the turbo is to blame as they seem to rarely fail...can someone give me a tip? I would like to do whatever I can (like valve adj.,filters,timing etc.) to get the most out of this rig but lack much experience with diesels...Thanks for any info! Mike

Do a search on checking the ALDA signal line and adjusting/removing the ALDA.

To start you off, and a lot of this is my interpretation, the IP is designed to provide fuel for the maximum turbo pressure situation. The ALDA is a device which limits fuel in indirect proportion to manifold pressure. No manifold pressure = maximum fuel inhibition, high manifold pressure = minimum fuel inhibition.

The turbo is limited by how much hot exhaust gas flows through the turbine. Hot exhaust gas is limited by how much fuel is burned. You start to see the catch 22.

A quick test is to remove the ALDA and check maximum boost. Note that with the ALDA removed you disable the overboost protection circuit. Overboost protection kicks in at 1.0 - 1.1 bar. That might be the 603 spec with the 617 spec being a shade lower. I'm pretty sure your engine was designed to be safe to 1.0 bar. I wouldn't sustain pressures beyond that. Bascially, all you want to do is see if you can get more than 10psi with no ALDA limitation.

If you see more boost, you can adjust the ALDA using the setscrew, adjust the ALDA by using a washer as a shim to raise the ALDA plunger relative to the IP, or keep the ALDA off the IP. Keeping the ALDA off the IP will result in exhaust smoke from overfueling if the engine can't keep up with how much fuel your right foot is forcing it to injest. A properly set ALDA keeps smoke to a minimum though over time the setting tends to drift to being overly conservative. If you join the camp that keeps the ALDA in the garage, be sure you understand the potential consequences.

If all that shows no improvement, take a closer look at the turbo. Is the wastegate flap completely sealing the wastegate port? Are there cracks in the turbine housing allowing exhaust gas to bypass the turbine? Are the turbine and compressor wheels in good shape? Does the shaft spin freely? Is there perceptible axial or radial play in the shaft?

Sixto
87 300D