Boost control switch
 

Haven't seen any info on this yet. I have 85 300SD Cali model. I pulled intake exhaust and T3 turbo off a 82 in bone yard. I rebuilt turbo and installed all on engine. Works absolutely wonderful except -- I am really pumping out black exhaust when excellerating . Also under Full throttle it will sporadically puff a cloud of unburnt fuel out. Could part of this be Cali and Fed boost switch is set different? Any thoughts on this would be much appreciated.

I'll take a crack. Black smoke is due to over-fuelling, as is puffing out unburnt fuel. Under no boost operation, fuel is limited by the IP. As boost builds, pressure on the ALDA allows the IP to deliver more fuel since there is more air. The overboost switch cuts positive pressure to the ALDA when it reaches the boost limit reducing fueling to the non-boost level until the pressure drops to a safe level. The wastegate in the turbo is designed to prevent overboost conditions.

The first thing I would check is to make sure the turbo is producing boost. It's possible the ALDA is messed up so it puts out max fuel whether there is boost or not. You can get a really cheap vacuum/boost gauge at Harbor Freight and just tee into the ALDA line to read boost.

Here's an image of the vacuum and pressure systems on an '85 (pressure in green)



http://www.peachparts.com/shopforum/...um-diagram.jpg

Yes havent been able to check boost yet. I have stripped all unnecessary equipment from vacuum system as making it a Fed version. It smoked more blue before because turbo was leaking into exhaust. Now just a black cloud. Sure runs nice though! Any way thanks for reply. I will just keep tinkering with it.