My boost gauge needle that is. I've noticed lately when minding my own business at 65mph, my boost shows 0, or a bit below. It'* pretty consistent now. And I feel I don't get the power I should when I punch it, and the boost doesn't peak where it used to. It'* CLOSE, but at WOT I'm usually at the last line before 10 (7.5psi) or slightly above. I didn't even hit 7.5 at WOT on one occasion this morning. Subsequently, my gas mileage doesn't seem quite as good as it should be either.

My fuel pressure is ok, actually higher than normal. But boost was never affected before as consistent as it is now.

BCS? How do I diagnose this?

Vacuum leaks...

Do the boost bypass trick for starters. Did you gain boost? If so, vacuum leak or faulty BCS.

Then at idle, disconnect the top vacuum line from the BCA. Does the BCA full-travel? Or only partial? If it doesn't fully actuate, vacuum leak or faulty BCA.

What is the boost bypass trick?

I'll try the vac line to BCA later.

If the BCA/BCS seem to be good...would a clogged CAT cause the boost to read 0 (high) when holding a slow speed? The biggest problem I have is that the boost is at 0 while driving normally. I'm not too worried why I was slightly under max boost.

What is circled there is the actual bypass. The actuator for the bypass (BCA, or boost control actuator) is indeed the black canister to the right. Disconnect the top vacuum line while the car is idling in Park. The actuator should travel fully as you disconnect/reconnect that top line. It should force the bypass valve (shaft coming from the SC) from rest on the hard stop for the foot, to a full 90° when you re-connect it.

In other words, at idle, it NORMALLY is bypassed. The shaft of the BCA will be fully retracted into the BCA, lifting the bypass arm up 90°, which opens the butterfly valve in the bypass in the same manner your throttle plate works. When you disconnect that top vacuum line, the BCA shaft should extend fully, until the bypass arm is resting on that little spot on the 'foot' of the SC. This is now unbypassed, simulating what it does when you mash the throttle while driving.

Just below the red circled area is the BCS (solonoid). It is what controls what the BCA does, based on PCM command. You will bypass in park, neutral, when braking, or when the engine load decreases. The nut is missing from the only retainer for the BCS in that pic. It has a vacuum line coming in along the left side of that red circle, an electrical connector from the PCM underneath, and a vacuum line coming out the right side (can't be seen from this pic). If you disconnect that vacuum line off the BCS (the little 'elbow' between the BCS and lower portion of the BCA), and plug it with a tic-tac or similar, then go drive, full boost will be restored ASSUMING your BCA is capable of full travel based on the above test.

If the BCA fully extends and retracts as detailed above, disconnect the little elbow from the BCS, and plug that end of the boot, leaving the elbow attached to the lower port of the BCA. This prevents the PCM from dumping boost, and can help you determine if you have a bad BCS or a vacuum leak, or some other problem.

That'* a lot of good info...!

Unfortunately (or fortunately) my BCA is working as it should when I disconnect the vacuum line. I checked all vac lines and they are connected nicely. The only vac leak I know of is the EGR tube which has a crack in it. But my boost was never consistently at 0 like it is now at 64-69mph.

I watched it on my way home, and I can hold 70, 71, 72 - 76... and the boost is very low (-7). But when I am at 64, 65, 66 etc (TC locked up holding 2000rpms), it'* at 0 or a little above. I'm stumped. It'* only at those speeds. There are a couple times I am holding 65 and it'* fine, but most of the time it'* at 0. I don't suppose the TPS had anything to do with it?

TPS should have little to nothing to do with it. The good news is that the fairly expensive BCA is good, and working properly when you test it.

NOW:

Disconnect the line that is attached to the driver'* side of the BCA from the BCS. Leave the little elbow attached to the BCA(ctuator), and plug it with something, or put tape over it. Go for a drive. I strongly suspect your full boost will be indicated. If it is, the BCS (inexpensive) or a vacuum leak around (before or after) is the culprit.

If it ISN'T better, we're looking for a leak that is causing actual boost loss (usually a SC outlet gasket) or a leak causing a bad MAP sensor reading. This MAP sensor idea would mean you actually DO have good boost, but the gauge is reading incorrectly.

We'll get it. One thing at a time, Pete.

I went for a little joy ride a while ago. Nice cool night. Car drove well, but still had boost hanging around 0. I did however get full boost at WOT. I don't think I'm concerned about the full boost. It doesn't seem to be a problem. Only the high boost readings at normal driving speeds.

I'll try those other things tomorrow.

Only problem I have lately is the amount of fuel that'* accompanying my full boost readings.

Pete.. when you detailed your engine.. you didn't remove any excess gasket material sticking out from under the charger did you?

Nope, didn't remove anything. Plus I did the engine a looong time ago. The SC gasket has been replaced recently too. All the gaskets I believe.

This morning: I was holding 65mph, and boost was at -5 (still too high). I very slowly decreased speed from 65 to 59, and my boost gauge slowly crept up from -5 to +1 in the process. Makes no sense why the boost increases when I'm giving it less gas.