No boost, need verification!
 

Hello all, first post, what an informative forum! I've got a 98 SSEi with no boost on the guage (goes up to 0, but that's all). I looked at all the posts on this, but need verification of what it is. When the engine is off, the BCA is extended down. When I start it, the BCA pulls the lever up to it's "vertical" position. When I throttle it, it moves in and out. I unhooked the line off of the top of the BCA, no boost. I unhooked the line going from it to the BCS, still no boost. I unhooked the line on the other side of the BCS, still nothing. I checked the T fitting under the charger nose and all lines seem to be in great shape. Is it my BCS that's bad? In all situations above the guage goes up to "0", but not past it. Is the lever that the BCA moves the waste port? Thanks in advance for your help!!

Sounds like the bypass valve is working to a degree.

It is possible that the PCM isn't allowing the valve to close fully, however this would usually be under knock retard situations.

I'm assuming this worked fine and this is a recent issue? Any low octane fuel added by mistake?

This may be a stupid question, but do you have the supercharger belt on?

Belt is on and does not slip. Tension seems OK. I can hold the BCA one way or the other and rev it and there is no change. Does the BCA dump the boost pressure or hold it when it pushed the rod down?

When you pulled the top line off the BCA, did the rod go all the way down?

Yes, it does.

Actually, I just bought the car in August, and have never owned an SSEi, so I didn't know the difference, until I rode in one WITH boost! Holy crap! So I started to check into it.

If the actuator fully travels when you pull that top vac line, you have either a vacuum leak on the BCS side, a bad BCS, or the PCM is limiting boost for some reason.

SOunds good. I think I'll replace the BCS (relatively cheap). Vacuum lines all look excellent. Where is the PCM? I don't think I asked clearly above, does the BCA dump the boost? I'm just trying to understand the system. Thanks for all your help! :D

Try this page (pic links are screwy, but you'll get the picture):

http://www.bonnevilleclub.com/forum/.../bearings.html

You'll see the bypass valve. You can also see the arm the BCA attaches to in order to figure out which direction is bypass, and which is boost. ;)

When the arm is DOWN (horizontal) you should be in boost. When the arm is up, you should be in bypass. At idle, it should be fully up until you remove vacuum to the top BCA port, then it should go fully down.

If it travels fully with this test, the problem is very likely the BCS.

Couldn't get the link to work....But I'll trust whatever you say, seeing you have your own site about it!! I see now how the BCA works and which way the lever moves in boost mode. (Down when I throttle it, up when idling...) So what does the BCS do? Control the BCA? Because the BCA seems to be working correctly.

The PCM commands the BCS to control the BCA based on gear selected, engine load, and various other parameters.

Think of the BCS as the go-between for the BCA and the Computer.

So doesn't that mean the BCS is working, because the BCA is moving when you throttle it?

When you remove that vacuum line from the top of the BCA and it moves FULLY, it means the BCA is CAPABLE of full travel/full boost if it's commanded to.

So now you move back to WHY it's not fully travelling when commanded. ;)

Man, quick replies!! :D Sorry to still be confused, but doesn't the BCS TELL the BCA to move when I throttle it? SInce it's moving, isn't the BCS controlling it correctly? Or is that not how it works? Sorry to ask so many ??? about it.

Do you understand duty cycle? The BCS is either OPEN or CLOSED. But it varies this by pulsing a duty cycle. This is how it VARIABLY controls the BCA.

Aaahhhh...Variably....I didn't understand that part. Thanks for your help. I'm gonna get a BCS and let you know how I make out. Thanks! ;)

Just a shot in the dark here, but have you tested the boost guage itself? Have you put a mechanical guage on the plenum to see what the pressure is when accelerating?

Motorhead, that's a great idea, but in our rather extensive experience on this Forum, we have yet to see a single failure of a boost gauge. To take it even farther, we've yet to see a single failure of a MAP sensor on the Series 1 (which sole purpose is for a boost pressure indication).

Let's stick to what we know are the most common failure modes.

Ordered the BCS today, $28. I'll let you know when it comes in.

Installed the BCS today--still NO boost. :cry: 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's only on NA engines? I thought that the supercharger was in place of the plenum...

Any hissing in the engine bay at idle?

From Wikipedia, the free encyclopedia
Jump to: navigation, search
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's 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's 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's 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's 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's getting a signal?

Before we check the BCS. we have to look at another issue. From your post, you describe your operation as backwards.

With the car OFF, the arm should be all the way down, with the BCA extended.
At IDLE, the arm should be all the way UP with the BCA retracted.
When you rev in park or neutral, it SHOULD NOT MOVE. The PCM should be in bypass.
When you pull the TOP vacuum line off the BCA, it should EXTEND, pushing the arm DOWN.

Verify your vacuum connections:

Attachment 57207

https://i14.photobucket.com/albums/a...lwren/bca2.jpg

Attachment 57208

The routing should be obvious with the red lines you see here. Ignore the unused port on the BCA (that's for a vacuum-relief vent, and most of our foam filters deteriorated long ago).

AFTER we figure out why yours is acting funny, you'll want to go back to the rear of the engine to check your connections (vacuum and electrical) to the MAP sensor. The MAP is a rectangular box on a bracket just behind the #4 fuel injector (between the SC and firewall, above the rear valve cover). Small box. One vacuum line, one electrical connector.

Do the carb cleaner test on this one too (at idle).

Man, thanks for such detailed help!

When the car is off, the BCA is extended like you said.
When idling, the BCA is retracted as well.

BUT, when I rev it in park, it extends/retracts.....

When I remove the top line, it DOES extend like you said.

My hose connections do not look quite like yours. Out of the BCS the line goes toward the front of the charger to a small round silver thing at a tee fitting, the other line off the tee goes under the charger nose to another tee.

I'm going to get a digital camera today and get photos of the routing, etc.

Excellent. That supercharger ever been off the car that you know of?

Whoops, I just noticed something.... he has a 98, therefore a S2. Isn't the vac line setup dramatically different?

It does look WAY different than the pics Willwren posted. As far as I know, the charger has never been off. It had 125,000 miles on it when I bought it.

So you're saying the BCA should NOT move when I rev it in park?

My goof. I was fixated on the older cars in your sig.

Check the TEE fitting under the nosedrive of the SC. Can someone please post pics of the S2 routing?

Sorry that its freaking huge.

https://www.autozone.com/images/cds/...3d8015e545.gif

That's mine, and it's hooked up correctly. Now I know the "small round silver thing" is the fuel press. regulator... :oops:

While using a mechanical gauge is good for many tests, the general feeling of the car should tell the poster if they have boost or not.