legacycentral bbs

So, my '93 SS 5spd came with a MBC already in place. It reads from the manifold (post TB, passenger side) as connected now. I've been reading up on the PTFB conditions/hesitation/high egt and how it is related (partialy) to the way the MBC is connected. I am also getting weird hesitation-acceleration off and on while at part throttle and/or when transitioning from PT to full throttle (nothing too severe it seems though). I have new plugs, air filter, and have also reset ECU.

My question is: where are you guys/gals connecting your mbc input line to before the TB?

I have an aftermarket A/W intercooler with custom AL piping from the turbo outlet to the intercooler so there is no pre-existing line to connect the mbs inlet to. Will I have to drill/tap a hole for the feed line? also, what is the upwards facing vac-looking line on the front side of the turbo (copressor side)? can I use this as a feed for the mbc?

I need to get an emmisions test soon, and I may just reconnect the stock BC to see if it runs smooth more consistently (as hesitations CAN'T be good for emissions readings )


thanks,
Chad (learning about FI as I go... )

There's a nipple right on the turbo's compressor housing, right by the outlet, for the exact purpose of supplying a boost signal for boost control. Right now it's probably hooked up to the stock boost control solenoid.

Most emissions tests are done at steady state, so hesitation shouldn't really matter. But excessive IATs might, if your state has 4-wheel dynos which can put the engine under load.

Thanks vrg3.

yup, here in CO we have tight emission standards and the tests are conducted on 4wd dyno's that mimic driving (0~50mph).

so that nipple IS something!! right now it is actually open (so essentially I have a 1/16" hole for boost to leak from? - great ) I will reconnect the MBC to that nipple and see how she goes (as well as plugging the vac line that the MBC is connected to now).

The stock BC is just sitting on the shock tower with it's inlet/outlet capped.

It was just sitting open, free to vent any boost that it can flow, and to ingest any grit that happens by? Wow. Yeah, fix that.

For the emissions test you might do best just hooking the compressor outlet nipple straight to the wastegate actuator. You'll only get 5 or 6 psi of boost but it'll definitely be smooth.

Also consider changing out your PCV valve if you haven't recently. I failed emissions, went home and changed out the air filter and PCV valve and then went back to get retested.

Passed with flying colors.

yup, it's just open. I was wondering where the light coating of oil was coming from that is in that area.... now I know
I'll probably will connect the compressor nipple straight to the wastegate actuator too - sounds like a good idea for curbing excessive emmisions (although I'm curious to see how it burns as-is, minus the fubar'd MBC connections)

I'll throw a new PVC valve on there as well - might as well for the $$. air filter has 2kmi on it, plugs the same....

Thanks for the advice fella's

connected the MBC to the compressor nipple - much smoother, especially in transition from part throttle to full throttle (no sudden 16+psi charge rushing into the intake spider)

my part throttle response is better as well, i.e. it's not so touchy, which gives better driveability.

Thanks!