is boost constant in each gear?

[yesitsme]

Hi all
 
I am wondering if the boost is limited byt the ecu in 1st?
I feel the pick up in all other gears and then a pronounced kick at 5k when im guessing the 2nd turbo says hello.
I do not feel this in 1st though
 
Is it just me?
 
cheers

[chrisJDM]

well you shouldnt really feel much of a kick when the second turbo comes in, should be quite smooth from 1st to 2nd.  I have a problem with my setup where my 1st turbo hardly boosts at all but the 2nd turbo works fine, so i do get a bit kick when the second comes in.  I seem to get the same sort of boost in each gear thou on the 2nd turbo.

[tezz12345]

i only ever get bout .3 or .4 in fist but good in all others i thought it was to stop crazy weelspin

[Martiny]

Often, 1st gear is too short to get full secondary boost. Can you try it up a very steep hill somewhere? This would make 1st longer and give the Turbos more chance of getting up to full boost.

Are you using a gauge, or just going by "feel" ?

[yesitsme]

im going by feel
i do get the odd pop and bang through the exhaust but im putting that down to the kikamoto exhaust being more free flowing.

[Martiny]

Feel is not going to be very accurate. A boost gauge would tell you for sure whats going on. Odd pop and bang nothing to worry about.

[Ricco_04]

I get 2nd tubbie in first.  Never looked to see if it\'s full boost, peak hold on the commander would just show full boost from 1st tubbie.

[Bobfish]

Date: Sat, 5 Sep 1998 11:41:28 -0500
From: "Steve Wynveen"

Yeehaa, my car is finally 100%, probably for the first time since I bought in April \'97. I also fixed my problem with always having low boost on the second turbo in 1st gear only. The problem was with the solenoid valve that controls the vacuum signal to the turbo control actuator (TCA). It turns out the bad solenoid was going open circuit when it got hot (from engine heat). This somewhat intermittent nature made it a true pain to diagnose. Luckily, the problem was getting worse this year & the low boost was cropping up more consistently. I now see 10 psi on the second turbo in 1st gear all the time...what a difference in acceleration!

I must also thank Peter Farrell for giving me some advice over the phone on the order to carry out my troubleshooting. Here is what I did, and the equipment used:

My already had a boost gauge in my car (installed late last summer). In addition, I purchased a vacuum/ pressure test gauge from Sears for $20, and already owned a vacuum hand pump with gauge (Mity Vac), a pressure hand pump with gauge (sold in personal watercraft catalogs - used for testing pop-off pressure on diaphragm carburetors), and a good multi meter. The low boost on the second turbo made the TCA suspect, in that it wasn\'t getting either the pressure or vacuum signal, both of which it needs to work correctly. Here is the test procedure:

1. Tee into the side fitting on the TCA, right next to the TCA. This is the pressure port. Go out and warm up the car thoroughly. Accelerate from 2k rpm at WOT in 2nd gear to well past the turbo transition point at 4500 rpm. Before the transition, the test gauge should read atmospheric (0 psi, actually 0 psig, but I won\'t get into the nomenclature). At the transition, the gauge should IMMEDIATELY jump to pressure (>7 psi ?) and hold as long as you have the gas mashed (don\'t hit the rev limiter, please). If you don\'t see the jump to pressure, this tells you that something in the pressure side of the control system is awry. I had pressure, so I didn\'t go down this road.

2. Tee into the fitting in the center of the actuator, the one that points toward the front of the car. I pulled off my plastic under tray for better access to the actuator (you don\'t want to drive you car for very long or had without the tray. I have heard of people overheating their cars without it). Again, tee into the line and go for a drive. With the car fully warmed, do the WOT test in 2nd gear from 2k rpm again. This time, you should see the gauge jump to vacuum at the transition, and hold. I saw no vacuum. In fact I saw a very quick jump to ~1/2 psi pressure, which immediately fell back to 0 psi. This is just because, on my car, the pressure side of the system was still enough to drive the TCA, only slower than intended. When the pressure pushes the diaphragm down inside the TCA, the vacuum side of the TCA reduces in volume, causing the quick, slight pressure spike.

3. So, we know I am getting no vacuum to the TCA. This means either that the turbo control solenoid valve has failed, the vacuum check valve has failed, a vacuum hose has popped off, or one of the other two solenoid valves in this vacuum system is stuck open, venting to atmosphere. The easiest to check was the check valve. I pulled out the appropriate check valve and applied 12 psi to it from the manifold side, to simulate running under boost conditions. The valve didn\'t leak, and shaking it around didn\'t make it leak either. Next, I drew vacuum through it, and it let vacuum flow in the proper direction. So, the check valve is eliminated. Next, plug my Mity Vac into the line coming off the check valve and pump the system up to ~ 15 inHg vacuum (a fair amount of pumping). The system held vacuum, indicating no major leaks when all solenoid valves are de-energized and no cracks in the vacuum reservoir.

4. Road test. Tee into the vacuum system either just PAST the check valve, or by the entrance to the vacuum reservoir. Go for a drive and do the WOT test from 2k rpm in 2nd gear again. You should see vacuum all the time, and a drop in vacuum as it gets used at the turbo transition point. When driving gently, the system should hold a high, steady vacuum. In not, something else in the system is wrong, possibly a solenoid valve. If, at the transition, the system drops to zero, or something very low, a vacuum line popped off somewhere is indicated. In my case, everything looked like it should, high stead vacuum (~20 inHg) with a slight drop at the transition (to ~15 inHg).

5. All indications at this point were to the turbo solenoid valve that runs vacuum. This is the one bolted to the secondary air control valve assembly. It is the valve NOT in the big rack of valves by the spider. On my under hood diagram (1994 car) it is item #12. At this point it must either be a bad solenoid valve, a blockage or pinched off line before or after the valve, or electrical. There\'s only one way to check this, pull off the extension manifold (yipee!). So, about 1.5 hours later I\'m down to the solenoid valve. (By the way, I\'d highly recommend gently stuffing some paper towels or rags in the 4 passages exposed on the lower manifold. It is just WAAAY to easy to drop something down there accidentally - like puke, sorry Isaac I couldn\'t resist -, and then you really have big problems.

First, I checked the valve by applying battery voltage across it by using jumper wires. The top terminal is +, and the bottom is ground. Peter Farrell told me that clicking is not enough to indicate a good valve. Sometimes they click, but the plunger is broken internally. So, I first used my Mity Vac to put the vacuum system into ~ 15 inHg vacuum (same place as used before). When I applied voltage it clicked, and I could hear the actuator move. This also eliminates a blocked or kinked off line to the TCA. Damn, I thought, an electrical problem in the harness. Just what I need.

6. Check out the electrical harness. I reconnected the battery & turned on the ignition (DON\'T turn over the engine - you\'ll suck up the towels in the manifold I recommended in step 5). This sends power to all the solenoids. The ECU runs them by grounding the other side of them. The solenoid valve had battery voltage. OK, it has to be the ground. So, I should pull out the ECU and measure continuity between the solenoid\'s plug (yellow/blue wire) the appropriate ECU harness terminal (#4R). However, there is an easier way. The electrical diagram shows that both turbo control solenoid valves (pressure and vacuum) are grounded by the same 1 wire at the ECU. Somewhere along the way they join together. We know the pressure solenoid valve works (saw pressure at the TCA in step #1) so its connection to the ECU must be fine. Therefore, we can just check for continuity between the ground terminals of both solenoid valves (valves #12 and #26 on the underhood diagram, ground is yellow/blue on both). I used a long skinny screwdriver as the conductor to get to the #26 valve without having to dig the valve out. I saw .2 Ohm. Damn, everything checks out, what the hell is wrong!!

7. Back to step 5. I played around with the jumper wires to the solenoid valve some more. At this point, things were still a bit warm, as I pulled the manifold off without letting the car cool for very long. All of a sudden, the valve stopped clicking. I pulled out the valve and did some more testing on a bench. It clicked again. I though to myself, maybe it is heat related. Next, I measured the resistance of the solenoid - 34 Ohm. Then, I pre-heated my oven to 175 deg F and baked the solenoid for 3 min. When I pulled it out and check continuity - open circuit. As the solenoid cooled, it began to show very high resistance and slowly came back to a realistic valve. Yipee, I though, here\'s the problem, a temperature sensitive valve.

8. I ordered up a new valve and manifold gaskets to get overnighted from Mazda Comp. Put the car back together, and it now works as Mazda intended.

In closing, I must thank Mr. Farrell for his guidance in getting me started. I must also say for shame to those mechanics that told me it was normal to not get full boost on the second turbo in 1st gear because it is so transient and the engine is loaded down enough. Also, as I discussed with Mr. Farrell, do you think any Mazda mechanic would have taken the time and effort to do the diagnosis like I did? It is much easier to guess a part is bad and replace it (making money on the part and labor to install) than it is to do a proper diagnosis. Not to mention, many mechanics don\'t have the proper training or understanding to be able to diagnose such a complex system.

_______________

Source: http://www.fd3s.net/boost_problems.html

[Bobbit]

I did a simple write up on how to check for faulty solenoids: clicky