After getting some breaking miles on my new engine (new from Mazda) I've been getting braver and braver and have run into an issue. Namely, the car looses all boost after 5k and doesn't recover any boost. Currently it spools up to 9 psi, and holds stead until right at 5K and then the boost drops like a rock and the car (obviously) looses power. If I let off the gas, then back on the gas the boost comes right back, and then drops again. The engine still revs, just very lazily.

Now, when I replaced the engine I took all the solenoids and actuators and tested them all about three times, trying to make sure I didn't have to dive into the rats nest again. One item of note, when I test the turbo control actuator it only moves under vacuum, if I apply boost then it does nothing. The FSM says to use compressed air, and the video under the FAQ follows the FSM, but I couldn't get any movement. Am I missing something? Out of everything I've tested while the engine was out, this was the only thing that I now question.

I'm open to other suggestions as well.

Thank you in advance!

 

The TCA isn't too hard to test. If it's failed it will have a torn diaphragm.

Push the rod in and put your finger over one of the nipples to it. Let go and the rod should come partway out and stop, then go the rest of the way when you take your finger off. Do the same for the other nipple.

If on either or both nipples the rod slowly comes out with your finger on the nipple it's a torn diaphragm that needs to be replaced.

Are your pressure and vacuum tanks holding pressure and vacuum?

Dale

 

Thanks Dale!

I gave another look at the turbo actuator and it holds vacuum, but when I apply boost the rod begins to move but clearly is leaking. Same with moving the rod and placing my finger on the port to hold it, on the boost side it leaks down, and the vacuum side holds fine.

Does this sound like a possibility? No wonder I didn’t catch it before...

I did check both vacuum and pressure tanks and both are solid on both vacuum and pressure.

 

Yeah that sounds like it's no bueno. I'd track down a good used one.

Dale

 

The saga continues.

Installed a good, tested TCA tonight. My problem continues, but with a slight change. Now the car goes to 9 psi until 4500, then drops to about 3 psi and stays there until redline.

I also had the car have zero boost after one run, even after letting off and hopping back on the throttle there was no boost.

Before I begins tearing into more items, I have to ask. Could this be an adjustment issue of the TCA? I noticed a procedure in the FSM, but I don’t see any paint marks to line up. I didn’t see much discussion about it (mostly for wastegate and pre-spool actuators) after a quick search.

Also, when I got the original TCA off the car I tested again, it wouldn’t hold one direction, just a slow leak down. So that should be an improvement, even if it was not the smoking gun.

 

You should definitely make sure your actuator rods are adjusted correctly in this process. But that is more of an efficiency thing. If your actuators aren't pre-tensioned a little you will bleed off exhaust gas and lose response.

In this case an adjustment of your TCA isn't going to change the fact that you have low boost after transition. After transition your TCA opens and so does your precontrol. You can't really adjust it to open more if it is getting pressure and/or vac to open. Also, even a small leak in the diaphragm wouldn't change this because it is being supplied with constant boost pressure to stay open. The vacuum is just added so it opens more quickly.

So several options here since you have decent primary boost and low secondary. In rough order of likelihood:

1. Your TCA isn't being actuated open. You've bench tested it so now tee into the pressure hose and vacuum hose going to it with an analog +/- gauge and go for a drive. See what happens. You can tee in up top. It doesn't have to be at the actuator. KeyONKeyOff should work the TCA if you have a good vac chamber, but it's not going to test if it is getting both pressure and vacuum.
2. Your charge relief is leaking. Either the valve itself or the short elbow part of the hose.
3. Test your charge control. You can do the same deal and test it with a mityvac and tee into it. But there is a KeyOnKeyOff test for it as well.
4. Your turbo intake hose is collapsing.

 

The KOKO (key on/key off) test only works on the stock ECU I believe. If you have a PFC it won't work.

Now that you have a good one next step is to make sure it's getting boost and vacuum going to it as stated - T your boost gauge into the lines and see what they do. Also if you have the 2 lines swapped it won't work.

You could also have a boost leak somewhere, that's not out of the realm of possibility.

Dale

 

If you have a leaky check valve on the vacuum side of the sequential controls you will also get normal primary turbo operation and rapidly dropping boost with 2ndary turbo transition.

 

Thank you all for the assistance! Tonight I was able to verify the charge control and charge relief. Both operate as described in the FSM. I did find the 90* hose going to the charge relief had a loose hose clamp. By loose I mean barely on there. That's been corrected now.

I also took a look at the TCA again, and it would appear there is just a little preload on the actuator with it closed. So, I will take that as being 'close enough' for my purposes at the moment.

I'm tee'd into the TCA line, so tomorrow I'll give those portions a closer look.

I'll also give a look at any check valves I can access. I've got my fingers crossed I don't have to pull the UIM!

 

I think you can get to the 2 check valves that handle boost and vacuum for the TCA without pulling the UIM. If you have old stock check valves, PM me for a set of my Viton valves.

Dale

 

Problem solved!

I had installed the check valve feeding the pressure tank backwards. So anything being fed from that tank was actually fed vacuum.

The clue was the line suppling boost to the TCA was actually supplying vacuum. So I would surmise applying vacuum on both sides of the TCA at once simply canceled each other out, and no movement occurred.

Even prior to the rebuild the car would nose over around 5k. I bet I’ve had that check valve backward for over a year when I had pulled the LIM on the original engine. I never dug into it knowing the other engine was on its way out.

Live and learn! Thanks for the help, it gave me some insight on how future troubleshooting might be. And I found a few issues along the way that I wouldn’t have seen otherwise.

 

Nice! Have you had a chance to drive the car at full power?

Dale

 

I need to hook up a better boost gauge to see just how things are working, but I can say it puts a smile on my face every chance I get!