Mystery plug/sender in the air inlet housing?

[Iceni John]

This is a Clifford-ish sort of question:

I'm trying to connect my new turbo boost gauge, but I've stumbled across something weird.   In the driver's side of the air inlet housing between the turbo and blower of my engine there is a mystery plug or sender.   It has a brass outer body with an external 1/4" MPT thread and 9/16" wrench hex flats, a smaller thread inside (sort of like a reducer bushing), but into this brass outer piece is a hollow steel shaft that has a 1/2"-long section of 1/4" hex and a 1"-long section that's about 0.145" OD.   There are two tiny holes about 3/16" from the end of this steel section;  they connect to the hollow section of the steel shaft.   The whole thing is about 2-1/4" OAL.   My Series 92 Parts Catalog in the Section 3.3004 Air Inlet Housing Adapter only shows a "Plug 8923847, 1/4"-18 pipe".   Unfortunately this Parts Catalog is for non-DDEC engines, so I'm not sure what this mystery plug is for.   The way it is now, some of the turbo's boost pressure can bleed through it, so should there be something else threaded into the small internal thread, maybe a boost sensor?   The DDEC boost sensor is on the passenger side of the housing.   My bus never originally had a turbo boost gauge, so that's not what it could have been for.

So, what is it?   I thought that would be a good place to have a feed for the 1/4" DOT tubing that will supply the gauge.   Can I instead just put a 1/4" MPT compression fitting in there for the DOT tubing, or is this mystery thing actually needed?

Sorry for the long-winded description!
Thanks, John
 

[Iceni John]

EUREKA !

I now know what this mystery thing is.   It's the injection orifice for the Quick Start ether injection system that my bus was fitted with from the factory.   The tube that connects from the control valve to this injection orifice is missing, but it would have supplied small shots of high-pressure ether straight into the airstream immediately after the turbo but before the blower.

The Quick Start system hasn't worked for years and I certainly don't need it now, so I'll put my 1/4" MPT to DOT fitting in there and connect half a mile of DOT tube to my new turbo boost gauge tomorrow.   That will be a filthy job as two decades of crud falls down on me while I put the tube along the frame rails  -  ugh.

So, if any of you have a Quick Start system on your bus, now you know!

John

[luvrbus]

I knew you would find the answer John life gets to easy here so I didn't answer you most had the Kat's system from the factory on the buses surprised me yours was the Quick Start system 

From time to time you will come across a air heater glow plug in the hole on the air horn that is my favorite cold weather system used along with the block heater

[HB of CJ]

But...the ether port makes a whole lot more sense.  HB of CJ (old coot)

[luvrbus]

I don't know about that Henry you get into some engines that had a heavy usage of either on the 2 strokes and the fire ring is always welded to crown of the piston a measured amount like DD wanted it doesn't hurt one but they will OD with too much