I've got low boost in 1st gear, so I'm checking my vacuum chamber. If I rev the engine in neutral it goes up to 15 or so, holds for 6 seconds and then drops back to 5. The drop is quick so I'm thinking it's a solenoid. It should just hold the vacuum, right ?

 

Could be a bad check valve. Check those too.

 

Get a hand-held vacuum pump with gauge found at Napa.

You can use it to check any chamber and all check valves, actuators, solenoids, etc.

It is THE best diagnosis tool to have with our complicated vacuum/pressure system.

 

Yes! It takes about 20 strokes to generate 20 inches Hg vacuum from the vacuum chamber. If it takes only 1 or 2 strokes, you've got a vacuum chamber full of oil. A worse situation is if the vacuum chamber doesn't hold vacuum at all (air leaks in), making it necessary to replace the vacuum chamber (a PITA--I've done this job!).

 

Isnt the vaccuum chamber the little black box on top of the engine? How is that a PITA to replace? Or is this not the vaccuum chamber?

 

The chamber on top is the vacuum chamber.

The one behind the power steering pump is the pressure chamber. THAT one is a BEATCH to replace.

 

The pressure chamber is the little box that sits between the crossover pipe and extension manifold (which everyone calls the upper intake manifold). That is easy to get to. Two vacuum hoses (under pressure), and two 10-mm bolts, and out it comes

The vacuum chamber sits underneath the alternator. Believe me it's not an easy job. Alternator, oil filler neck pipe, intake elbow, intake--all come out--just to get at that damned vacuum chamber!

 

Ahh, ok. Now I understand what is the PITA. I was starting to get concerned at what you thought was hard work, if that little one on top is a PITA then an oil change must really be hard!

 

if one of them is bad I have both sitting in the garage... fs.

 

Update: I teed into the TCA vacuum line. It jumps to 15in at the transition, which I think is correct. Strange because the vac chamber doesn't seem to have 15 in available.

 

Update: The vacuum chamber seems fine. Am I correct in assuming what that the lines to the solenoids connected to the vacuum chamber (CCV,TCA,CRV) should be airtight ? Also, is the colored vacuum diagram incorrect ? It shows a vacuum line and a pressure line to the TCA under the UIM. Shouldn't one solenoid have vacuum and one pressure ?

 

Not sure what you mean, but the hoses should be attached to the nipple rather snugly.

Quote:

Also, is the colored vacuum diagram incorrect ? It shows a vacuum line and a pressure line to the TCA under the UIM. Shouldn't one solenoid have vacuum and one pressure ?

Nope that's correct. There's a pressure and a vacuum line to the TCA solenoid near the ACV. There's a TC solenoid on the solenoid rack, and this gets vacuum only.

 

I meant can I test for leaks by applying vacuum or pressure to the lines the vacuum chamber is hooked up to. I did a little more research and I think at idle, I can test this way. (The TCA solenoid would need to be ON).

How could this be ? It's a two way solenoid. So it has to just have pressure and the connection to the TCA.
From Wades site :
When the ECU applies no voltage to the Turbo Control Solenoid, the passage is blocked. Vacuum from the vacuum chamber is applied to one of the nipples. When 12V is applied by the ECU, the valve opens and vacuum travels through the solenoid.
His diagram looks right to me. Wades site

 

There's a turbo control actuator solenoid near the air control valve, and a turbo control solenoid on the solenoid rack. The TCA has a pressure and vacuum nipple.

 

There is an error in the diagram that's stuck to the hood. As I recall, the part number with an "A" is wrong, and the part number with a "B" is correct, but that was a while ago, so better check with those with better memories. I tried to order the corrected sticker, but it was unavailable.

 

I don't think so. If you look at the diagram, it only has two hoses. What would the point be of connecting the pressure tank to the vacuum tank ?

 

The turbo control actuator solenoid controls the turbo control actuator. The turbo control actuator operates using BOTH pressure and vacuum.

Please refer to the '93 Rx7 factory service manual for more details.

 

Well, page F84 shows two solenoids. One has pressure and TCA, the other has vacuum and TCA.