2) Check that the air path from the intake manifold's boost fitting to the ALDA on the injection pump is clear. The small lines and changeover valve can plug up with soot from the EGR. 350's don't have a cat so it's likely not an exhaust problem.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

When we pulled the head on my 91 350SDL we found theintake clogged with black gooey carbon build up. There were places about the size of a pencil with all the clogging. After cleaning all that out the car had a lot more power up in the rpm ranges.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.