Enervation

I'm a fairly new FD owner (had it for less than 6 months), and noticed that the secondary turbo wasn't boosting properly - it was sitting around 6 PSI. The primary has always boosted fine, at 10 PSI with no noticable spiking.
So after fixing the odd brittle vacuum line and check valve, the issue still remained.
I had a look at the site http://www.autosportracetech.com/RX-...leshooting.htm where it mentions:

This seems to match the symptoms, but as I'm sure the last time the connectors would have been touched was over 5 years ago when it was rebuilt, it does seem unlikely (the previous owner was almost 60, perhaps he spent much of his time below 4500 rpm).
Anyway, so I went pre-emptively replaced a few more brittle vaucuum lines and decided to check the wiring.
The wire colours were rather faded and no noticable dot existed on either of the connectors (but it was on the right hand solenoid - wastegate control), but after checking the wiring diagram it definitely appeared to be swapped (the Blue/Yellow wire was going into the wastegate solenoid). So I tentatively swapped them over and, lo and behold, it was boosting at 10-something-10. It was at night, raining, and going well over the speed limit on a narrow road meant it was a bit hard to catch the transition boost level. However, it now has a kick at 4500 that wasn't there before and the 6psi secondary boost is long gone.
So that appeared to be successful, although I still want to ensure that the vacuum lines going to the two soleniods weren't also swapped over (which would cancel out the connector swap).

After a wee search on here, it appears it is quite a common problem.

Now, this got me thinking.
If the wastegate and pre-control soleniods are swapped, then the waste gate is being opened at >4000rpm, and always shut at below 4000 rpm. This definitely explains the 6psi secondary boost level.

The precontrol door would have been acting as a 'wastegate', and opening whenever boost got above 10psi. However, I'm guessing the precontrol door is rather small, and probably not a very good wastegate. Also, the second turbo would have been boosting, with the Y pipe gate shut, and the charge relief closed? - producing rather large pressures in it's short section of the Y pipe. This can't have been very good for the secondary turbo.
Now, back to the wastegate opening the pre-control door - why wasn't I seeing massive overboosting as the exhaust wasn't being diverted properly above 10psi? Was the pre-control door enough?

I'm still trying to understand how the vacuum/turbo system works in this beast, so I may be getting confused as to how things operate.
My main concern is: If the car was running with these two solenoids crossed over, for over 5 years, and having done ~25,000KM (15K miles) like that, would any serious damage have been done? It's only mods are pod-filters (and no pre-cat, as it is a japanese import to New Zealand, not a US model).

Also my first thread here, thought I should say Hi! Forums like this should make owning an FD so much easier

adam c

iTrader: (2)

One of the two solenoid connectors should be marked with a white dot. It should be connected to the solenoid with the white dot. Many times they get switched, hence low secondary boost.

arghx

iTrader: (3)

I have covered sequential boost control logic extensively here: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/why-engine-so-damn-complicated-part-1-sequential-turbos-demystified-841821/

Here is a Power FC log of sequential turbo solenoid behavior:



another log:



Yes but the wastegate would have been acting like a precontrol and thus stayed open far more than it should have, bleeding off exhaust from the turbine wheels. Normally (with the connectors not swapped) the precontrol is closed under low rpm, before it's time to prespool the secondary turbo. It's always at least somewhat open during prespool and then fully open after transition.



a lower duty signal effectively means less boost generated by that turbo. So with the two plugs switched, during spool you would have the wastegate flapper at least partially open. Technically that should hurt spool on the primary turbo at least some. The precontrol flapper would be completely closed (just like the wastegate would be normally), which would hurt prespool of the secondary turbo until the turbo control solenoids engage at transition.



After transition, with your reversal of the connectors the precontrol would be partially open (probably causing at least some backpressure in the manifold) and the wastegate would be completely open. With the wastegate completely open (as the precontrol normally is after transition), you are bleeding a ton of exhaust off from the turbine wheels.

Before transition, the precontrol was shut but the wastegate was open (just as the precontrol would be open if you hadn't switched them), so exhaust was still bleeding out. After transition, the wastegate was completely open (just as the precontrol would normally be), keeping your boost very low.

It's hard to say for sure, but the only thing that could be "bad" is a partially open precontrol valve after transition. That might cause a bit more heat inside the manifold which can't be good for everything down there. I'd say there was probably no real harm done, just a slow car. Hell, the lower boost may have extended the life of the engine internals.

Enervation

Thanks for that arghx, it's cleared a few things up.

From this, and looking at your graphs - very useful btw, thanks , it's clear I've misunderstood how the stock ECU controls the precontrol door. I assumed that it was fully closed below 4000rpm, regardless of load, boost or throttle position. And above 4000rpm it would open and stay open until dropping back below 4000rpm.
The graph seems to prove me wrong, and also explains the lack of boost spiking.

I'm just curious, as it seems to be a rather common issue, yet I would have thought the consequences of not having proper control of the wastegate would be catastrophic.

I might switch them back (to the crossed over state) in the weekend and just confirm the old behaviour, then swap back and compare again. Just to be 100% sure!

arghx

iTrader: (3)

That is how the turbo control behaves actually. You can see it as the green line in the very top graph of the first image I posted.



The 5500 rpm mentioned here in the FSM pinout is presumably for low throttle. The PFC is set to switch at 5400 rpm at 20% throttle or less. Look at the upper left corner of the very first image I posted.

Enervation

Thats quite reassuring. It seems to be running fine. As for it being slow before - it was still a hell of a lot faster than my Nissan Bluebird daily (Ultima for you fellas in the states). And it still managed a 16.5 1/4 mile in the pouring rain with puddles all over the track! (That was the time at which I realized it wasn't boosting properly).

Thanks for the help. I'll do some more checks this weekend and post the results.