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Sequential Issues: Turbo Control Actuator Sticking Open
I’m having a hell of a time figuring out what’s going on with my car. 93 FD with a Power FC ECU. Simplified sequential vacuum setup. No emissions equipment.
If I drive and keep the RPMs under 4000, the car boosts fine and everything is honky dory. Then the first time I go higher than 4000 RPMs, the secondary turbo comes online and boosts fine. After that, I have almost no low-end boost (2-3 PSI max) and a very loud exhaust note below 4000 RPMs. Then when I reach approx. 4000 RPMs again, I get normal boost pressure all at once. It’s a nice kick but not ideal for cruising around.
I found out that the turbo control actuator is getting stuck open. After a high RPM drive, if I unplug a vacuum line going to the pressure chamber (with the car running or not), it releases pressure and the turbo control actuator moves back to the closed position. Then the car boosts fine again, until I go back over 4000 RPMs.
I found that the large vacuum line going to the turbo control actuator (from the turbo control solenoid, so vacuum supply) had split. I replaced that line, no change. So I replaced the entire actuator. No change. Actuator still sticks open.
Things worth mentioning:
· I have redone the vacuum hoses numerous times, confirmed the correct routing.
· All new vacuum lines and check valves.
· Replaced all 3 actuators with used ones (turbo control, wastegate control, turbo precontrol).
· Replaced the turbo control, charge control, and charge relief solenoids with new ones.
· Replaced the turbo control solenoid with a used one that tested good.
· No cracks on the exhaust manifold/turbos.
· Smoke test did not reveal any vacuum leaks.
Can someone help before I bite the bullet and just go single?
How much boost are you running? The solenoids tend to stick at higher boost levels...
I essentially made a bleed for one of the big lines that goes to the actuator, that way pressure on that side of the solenoid drops down enough for it to unstick and resume sequential operation.
How much boost are you running? The solenoids tend to stick at higher boost levels...
I essentially made a bleed for one of the big lines that goes to the actuator, that way pressure on that side of the solenoid drops down enough for it to unstick and resume sequential operation.
Thank you, that makes sense. I run around 12 psi. How did you make your bleed line?
I used a plastic double male barb and pricked a hole in it with a pin. Something metal would probably hold up better, but this has worked fine for years.
I used a plastic double male barb and pricked a hole in it with a pin. Something metal would probably hold up better, but this has worked fine for years.
Easy enough. And you put that in line with the larger vacuum hose going to the turbo control actuator?
You will find your culprit to be turbo control solenoid 'E' located on the rack. It is really the only solenoid that is problematic. The short story for this particular solenoid (and only this solenoid) is that some of the units often seem to 'stick' because they have insufficient internal return spring pressure (acting on the plunger) to overcome the boost pressure working against it. So when it is de-energized, it does not drop-out as intended. I measured one that refused to drop out and vent until the TCA pressure was reduced to about 2 psi; obviously not going to work. None of the others, iirc, are affected because they use they solenoid to pull against pressure, therefore no problems. It seems as though Mazda re-purposed an emissions solenoid that wasn't designed to release against pressure--it is not an inherent fault with the sequential system design, per se.
I wrote about this TCA/solenoid problem at length elsewhere on the forum. Search on "turbo control solenoid E" or something similar and you should be able to find multiple posts (they're old). I also posted up somewhere on here, a simple work around bleed utilizing a check valve that will eliminate the problem for good--and without having to change the solenoid, add regulators, etc... You guys that are putting bleeds in are certainly on the right track. Some have gone to the extent of replacing all of the solenoids with industrial units--works but is expensive and overkill really--this problem isn't that complicated. If I were to change that particular solenoid (E), I would put in something more robust--a 3 port mac valve similar to what is often used for aftermarket boost controls will work; but it's only really necessary in that one slot.
^I think this is the right track. The big thing here is that it is OPENING AND STAYING OPEN. That's a key point.
The fact that it's staying open says that the TCA has a good diaphragm and isn't leaking down. It has a steady supply of either vacuum or boost to hold it open, so the check valve/tank is good. The problem is the solenoid that switches on and off the vacuum or pressure isn't doing its job, it's sticking and not returning to the "off" position.
This is one of those things that T'ing the boost gauge into the feed line can really pinpoint the problem for troubleshooting. My guess is you would see the pressure line at atmosphere, transition, see boost, then continue to see boost once you go to low RPM.
12psi isn't a lot on the stock solenoids, 14-17 psi is really where you need to worry about how much pressure they see. I would start with replacing just the one solenoid with a good used or new one then go from there.
Thank you all, that is very helpful. I searched through some of 'Speed of Light's posts and found some useful info. The turbo control solenoid 'E' is new but is a stock solenoid, so I see three options:
1) Replace solenoid E with a industrial type air solenoid (which I already have).
2) Add a bleed valve in line from the TCA to solenoid E, like a brass vacuum line coupler with a hole drilled in the middle.
3) Get a pressure relief valve, set it around 8 PSI, and put that on the line between the pressure chamber and solenoid E.
I'm leaning towards replacing solenoid E with a beefy one, and at the same time putting a T and another boost gauge on the line from the actuator to the solenoid and seeing how it behaves while driving the car.
Can someone confirm if I'm understanding everything correctly?
Replace all your sequential solenoids. It costs less than 300 dollars for new OEM. Replace them like you replace your tires or your brake rotors. They are wear items. Don't troubleshoot and replace piecemeal, you will go nuts.
there is nothing wrong with the stock solenoids except that they unfortunately don't last forever. Replace them and never worry about them for like another decade. See my thread for part numbers. Attempting to engineer another solution makes for an interesting project but it's completely unnecessary and not guaranteed to last any longer.
Replace all your sequential solenoids. It costs less than 300 dollars for new OEM. Replace them like you replace your tires or your brake rotors. They are wear items. Don't troubleshoot and replace piecemeal, you will go nuts.
there is nothing wrong with the stock solenoids except that they unfortunately don't last forever. Replace them and never worry about them for like another decade. See my thread for part numbers. Attempting to engineer another solution makes for an interesting project but it's completely unnecessary and not guaranteed to last any longer.
3 of the 4 rats nest solenoids have already been replaced with new, stock ones. The 4th solenoid (the unusual looking one that mounts by the ACV) has been replaced, tested good, and works as it should. The solenoid pair that bolts to the UIM is original and tested good, but from my research I don't believe those to be the culprit for my issue.
I teed a boost gauge into the line going from the TCA solenoid to solenoid E, will report with I find after a drive tomorrow. Hopefully it's just sticking once boost is applied...
I got the same exactly issue as you.I take the car out for a drive it drive normal until you boost it. First boost turbo boost fine and after that boost get up slow until rpm get to 4000 and boost up again .So after the drive i get home and jack the car up to take a peak The TCA vacuum arm that open and close the flap door on the manifold was in the open position pulling toward the actuator. I don't know if that the way it should be after the drive.So i start doing what K-tune said get a brass doudle male barb and drill small hole and connected to the E solenoid and it works.I think you should try it .
Car is fixed! What a rocket with properly functioning turbos... Thank you all for your help.
I took it for a spin this morning and confirmed that the line going from the turbo control actuator to solenoid E was holding pressure when it shouldn't be. One pull past 4k and it shot up to 1 bar and stayed there after returning to idle (the needle is slightly off, it's an old gauge). That confirmed the solenoid was sticking open and not letting the line vent when it should be.
So I rigged up a vacuum hose coupler with a small hole in it, and viola, proper boost. I'll replace it with a brass coupler eventually. If I have any issues with it, I'll give Speed of Light's method a try.
So now I know new solenoids aren't always what they're cracked up to be... Thanks again for everything!
Last edited by BrettLinton7; 10-27-17 at 08:34 AM.
Cool, looks a lot like mine. I replaced my solenoids while having this problem and noticed that even a brand new one stuck at around 16psi. We need to keep in mind the pressure source is right off the outlet of the turbos for the pressure tank(pre intercooler and any other restrictions), so it will be at a higher pressure than what your manifold sourced boost gauge will see.
Of course there are other/better ways of fixing this problem, but my "cheap bastard" method does the trick :]
Cool, looks a lot like mine. I replaced my solenoids while having this problem and noticed that even a brand new one stuck at around 16psi. We need to keep in mind the pressure source is right off the outlet of the turbos for the pressure tank(pre intercooler and any other restrictions), so it will be at a higher pressure than what your manifold sourced boost gauge will see.
Of course there are other/better ways of fixing this problem, but my "cheap bastard" method does the trick :]
Would this work even if I put that “holed connector” near the turbo control actuator (pressure side) itself? Or does it have to be up near the solenoid rack? I was just thinking if it might be easier that way since I might get the turbo control solenoid confused with another in the rack!
10-25-17, 04:10 PM
