1st gear secondary boost
 

anybody have any idea why the secondary turbo wouldn't boost in 1st gear? 95 FD, with PFS computer installed and O2 unplugged. 2nd and 3rd were fine

TCA. (99% positive) Either the pressure or vacuum side isn't working properly.

1. Does your TCA cycle when you turn the ignition key on and off (without starting the car)? Does it cycle when you start the car? If not, it could be the ECU, but check the following first.

2. Verify both the vacuum and preesure tanks are holding. With the car shut-off, preferably for at least 1/2 hour after driving the car and fully boosting, pull a line off the pressure tank and verfy it was holding pressure. To check the vacuum tank, disconnect the CRV vacuum line. You should here air entering the removed line. If either isn't holding, you probably have a bad check valve.

3. Verify that both the vacuum and pressure sides of the TCA hold and the TCA strokes, by applying pressure and vacuum directly to the TCA (with a Mighty Vac or something similar). 10-12 psid will fully stroke the TCA. As well, 15-20 in*hg will fully stroke the TCA. You have to get under the car to do this.

4. Check that you are getting both vacuum and pressure to the TCA while driving. You can tee in either at the actuator or behind the alternator. (if you study the vacuum diagram, you'll know what I'm talking about). The pressure side should show 0 psid below 4500 rpm, 8+ psid at 4500 rpm, and 10+ psid after 4500 rpm. The vacuum side should show 0 in*hg bellow 4500 rpm and 15-20 in*hg above. If you see pressure on the vacuum side of the TCA below 4500 rpm, you have a bad check valve on the vacuum tank. This check valve is notorious for leaking under boost and applying pressure the the vacuum side of the TCA, which causes slow transition and low secondary boost in first gear.

5. The TCA pressure side solenoid (the one mounted all by itself near the air bypass valve) is also notorios for failing. Unfortunately to check this, you have to pull the upper intake manifold. Ohm it out when it is hot (throw it in an oven at 250-275°F for 1/2 hour). It may ohm out ok at room temperature, but when hot, they often times go open. Also, verify it holds pressure. While your in there, verify that all the plumbing and vacuum hoses to the TCA hold by applying pressure and vacuum. Tee in by each of the solenoids.

6. Verify the vacuum side solenoid ohms properly (probably want to do this when it is hot as well). This solenoid is a PIA to get out of the rack though. And be gentle when working with it. The nipples get very brittle from all the heat in the FD engine bay.

7. Ohm out the wiring harness form the ECU to the pressure and vacuum side solenoids. I have heard of people having wiring harness problems (especially to the pressure side solenoid).

8. If everything else checks out OK, it may be your ECU. I am currnetly at this point in a similar boost troubleshooting issue. The problem is finding an ECU to borrow for a few minutes.

Good luck. If you need more help, PM me.

Glenn
'93 CYM