Installed the BCS today--still NO boost. Don't know where to go from here.

BCA?

Seeing as how shotgunning parts at it is not fixing it, maybe we should try to diagnose it instead?

Dumb Chic question... aren't plenum'* only on NA engines? I thought that the supercharger was in place of the plenum...

Any hissing in the engine bay at idle?

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Plenum may refer to:

the antithesis of a vacuum; in other words, completely-filled, positive-pressure space.
the pressures slightly above atmospheric, usually inside air or gas systems as the result of the action of fans or blowers. The plenum is measured in small units of pressure such as pascals (Pa) or ounces-force per square inch or millimeters of mercury.
a legislative meeting in which all members of the body are present and voting. Frequently this is used to refer to a full meeting of a Communist Party central committee. Compare to quorum.
a second set of bellows in devices such as hand or foot pumped organs with a weight on the top which acts as an air reservoir.
Plenums in buildings are enclosed spaces that are not for human occupancy, but are often used for heating, ventilating, and/or air-conditioning equipment and airflow, and for other equipment such as cables, piping, and luminaires. 'Plenum boxes' or sections are portions of HVAC air handlers or terminal units.
Plenum cable refers to structured cabling permitted under building codes for plenum spaces. Plenum rated cable has slow-burning, fire-resistant casing that emits little smoke
Plenary session
Plenum filtration, a method of aquarium filtration using a deep sand bed with a gap below it.



The word plenum can mean many different things!

Step 1: Verify that the BCA moves FULLY up and down when at idle, you disconnect that top BCA vacuum line. If it doesn't, replace the BCA or look for a vacuum leak. If it does, go to step 2.

Step 2: Spray carb cleaner on every vacuum line around the bca and bcs at idle. Does the idle change? If so, you have a leak.

Step 3: Suspect a possible MAP sensor issue. Check for a vacuum leak there or corrosion on the connector.

LASTLY: suspect a possible problem with the gauge. We've NEVER EVER EVER seen a bad boost gauge with 7000 members on this Forum. And I don't recall the last (if ever) MAP sensor failure either.

I'm trying to point out the obvious typical stuff, but leave the door open to the extremely rare nearly impossible that Motorhead is pushing.

Here'* a quick little lesson.

The BCA will act on its own controlling the wastegate unless the PCM steps in and commands the BCS to supply boost pressure from the LIM to the lower chamber of the BCA over powering the closer to atmospheric pressure in the upper chamber and opening the wastegate. If the PCM is not indicating boost cycle at less than 100% and a new BCS didn't fix the problem, it leaves few options.

1: bad BCA. Pull the top line off the BCA at idle, if the rod goes all the way down, the BCA is fine.

2: Vacuum leak between the SC inlet and BCA upper chamber. I've had big honkin' leaks elsewhere (not directly between the SC inlet and BCA) and the BCA still acted normally. But I wouldn't rule out remotly located leaks completely.


Now, here'* a test you can try. Pull the top line off the BCA. If the rod goes all the way down, get in the car and give it a few revs. If you don't get any positive pressure then, you've got a leak between the LIM and MAP or a bad MAP/associated wiring.

Hell, maybe your wastegate broke. It'd be the first time I've seen it.

Can you get us a clear pic of the rod below the BCA?

Ok, I'll try to give the best explanation possible. When you first start the car, the guages do their little self test. At idle, the BCA is pulled all the way in/up. When I rev it the BCA goes out/down all the way, then back up again when I let off of it. When I take the top hose off, the BCA drops down and I can feel the strong vacuum on that hose. When I hook it back up, it sucks the BCA right back up again. It'll do this whether the BCS is hooked up or not to the bottom of the BCA. I assume it'* supposed to, correct? I haven't sprayed carb cleaner yet, but can do that ASAP. I do NOT seem to get any positive pressure on that top BCA vacuum line when I really rev it, and assume I should seeing it'* attached to the same nipple assembly the brake booster is on. Don't know where the LIM and MAP are yet, but learning every day. Thanks for your help so far.

Is there a voltage value I can measure on the BCS plug to see if it'* getting a signal?