Hi Guys,

I have had a quick look round the forums and have found similar threads but without a definitive solution, so I am going to post all the information I am finding as and when I am finding it so that it might help others in the future.

Symptoms:

1) No primary boost, slow to accelerate until ~4500 rpm.
2) Normal operation after 4500 rpm
3) Secondary turbocharger works fine, stacks of secondary boost, normal operation.

Car Specs:

1997 Efini Series 7 FD3s
Japanese Import
Stock sequential turbocharger set up (including Vacuum Solenoid Housing : Image attached)

Suspected Cause:

Non functioning solenoid within the vacuum solenoid housing.

------------------------------------------------------------------------------------------------

The easiest way to diagnose that there is a problem here is to eliminate all the other alternatives. I would strongly advise working your way through this thread as it is how I started my investigations : Turbo / Boost Problem Troubleshooting

The reason I am getting no primary boost is because the "CHARGE CONTROL (ACTUATOR)" is not in the ON state at idle. The normal operation for this actuator is ON until 4500rpm, then OFF after that. You can read the aforementioned post to further understand this.

Killing 2 birds with one stone, you can check that you are both generating vacuum, and have a functioning actuator by routing a piece of vacuum hose from the vacuum chamber to CHAMBER A of the charge control actuator. If you then switch on the engine, you will see the actuator switch ON. This proves you have both vacuum and a functioning actuator.

The next thing to check is that you have no pipe leaks between the actuator and the Vacuum Solenoid Housing. I ran the same spare piece of vacuum hose from the actuator to the vertical nipple closest to the front of the car on the control box (picture attached, port on solenoid box circled in red). I also ran some spare hose from the vacuum chamber into the solenoid housing box to be sure that wasn't leaking either.

After doing this, my actuator failed to switch ON. Therefore I am assuming that I am losing vacuum somewhere between the vacuum chamber input on the solenoid box and the charge control actuator output of the solenoid box.

Now I have seen posts saying that this box cannot be dismantled to replace a broken solenoid. From here I have a few plans:

1) If it is definitely the solenoid that is broken, I will order an older series solenoid from when the rats nests were all separate solenoids. I will then divert the respective vacuum hoses away from the solenoid housing box and into a new solenoid so that it still functions properly.

2) If there is an electrical problem, then it will be a whole new post and new adventure

3) I have concluded that I am getting no vacuum on hose to the charge control actuator. However above 4500rpm this is supposed to supply the boost from the secondary turbocharger. I have yet to check if this is the case. Later today I will get a helpful volunteer to sit with his foot on the accelerator to see if I get any pressure at all. I am not sure what I am hoping to find from this. If I do see pressure then I will just assume that the solenoid is stuck diverting air from the turbo to the outlet. If I get no pressure at all, then perhaps there is another fault in the vacuum solenoid housing, such as a blockage or a leak.


From here I can see myself fixing the problem in 3 ways:

1) As above, buy a series 6 individual solenoid, and run it separately from the vacuum solenoid housing box.

2) Find a leak or blockage, or a loosely connected solenoid wiring fitting, anything that I didn't spot before that will fix the problem

3) Buy a new vacuum solenoid housing. These are currently going for about £400 new, which I would rather not spend.

 

You are wrong, the box COULD be disassemble. I rebuild the whole thing lots of times. and you can order the solenoid from Mazda Japan.

Most people on rx7club had no experience in this Box because it was never released in the US, the plugs/connector is different, emission harness length is different, so most just skip and never use this.

I had lots of experience because I work overseas now to fix all these rx7, and after so many disassembly I can rebuild the whole box in about 2 hour (taking my sweet time)

This box's solenoid is much MUCH better than any of those hitachi crap in zenki (1993-1995 in US) Rx7. but they could and they do fail overtime.

keep in mind tho you have to be EXTREMELY careful, this box is made of ABS Plastic and it WILL break if you pry it too much on 1 side.

 

Thats really interesting, do you have any more information on actually doing this rebuild? If not would you be willing to give me a few pointers on this so that I can make a detailed post about it. If I could rebuild my box that would be an ideal situation, although I have no choice but to put a zenki solenoid on for the time being.

 

Hmm, Well, u first gotta remove the pin on both sides first, spray some lube first tho. WD40 sucks so use some silicone stuff. move the pin around and u will slide it out

then start prying the box 1 side first, do it SUPER slow, and do it equally, like if u move 0.1 inch on 1 side, go the other side try to move it another inch. don't force anything or it will break (and that will cost u a lot)

after a while ur screwdriver (I assume u gonna use that to pry it apart) will no longer be able to pry it cuz the gap will be too wide, at that time use your hand to pull it apart slowly on 1 side , then the other, repeat.

DO NOT TOUCH ANY OF THOSE @!#!@# plastic nipple, nothing that seems "weak" to you, just remember this damn thing is plastic, if it breaks you are SOL

a good 5-10 minutes should be enough to get the box apart.

Just do it very very gentle and u will get it apart, do NOT rush things.