My 1984 BB512i (51723) , as part of the CIS injection system, has a vacuum limiter on each bank of cylinders. Each is located underneath each plenum on the forward end, held in place by a large clamp. Interestingly, these parts are NOT shown in the factory parts manual on page 7, which shows the components of the fuel injection system. These were OE on my car as the bosses for the hose connections on the forward end of each plenum and else where are used. That is, the bosses were drilled and taped and factory hose bibs were used. I have the factory fuel injection service manual for the 1984 400i, (which also uses the same CIS system), and I am to understand that this manual is also used as the service manual for the 512i. In this manual, the vacuum limiters are shown and referenced. In addition, Boxer 52935, the last built, has these limiters installed as well. I know this because I have personally seen the car. Attached is a picture of the limiter on 52935. Image Unavailable, Please Login I checked the FI diagram for a 1985 Testarossa, which uses the same FI system and the vacuum limiters are referenced there as well. As described in the FI service manual (two sentences), the limiters operate during deceleration to keep system vacuum below a prescribed level. So, I was just wondering if these devices were only installed on the later model BBi's, and if so when and which serial number did it happen? Also, if anyone has info on nuances of the CIS system in these cars, I'm sure it would be good info to have.