The few black-box cars we have run codes on show at least one solenoid in the box is shot. Usual course of action is to replace the entire box.

Its a 30 minute job, if you are used to pulling the UIM.

 

My Original Post was asking why the PFC was reacting my lack of boost issue the way it was. It seems that PFC wastegate control is a black box and nobody really knows how it all works.

The best discussion of PFC Boost Control that I have found is here in this 2004 post: https://www.rx7club.com/3rd-generati...1/#post9235043 and the diagram in this post: https://www.rx7club.com/3rd-generati...1/#post9238517 might explain why the PFC decided to reopen the wastegate at about 6,700rpm in the second screen shot of the Original Post when boost had been static and well short of target.




The block diagram (for the stock ECU) indicates that RPM is one of the parameters feeding the control algorithm. This thinking might well have been applied to the PFC algorithm. Looking at other long pulls that session the PFC always re-opens the wastegate at approx. 6,700 rpm even when well short of the boost target. I speculate that it shifts to another algorithm at this point. The wastegate change at these revs varies and I have not spotted a consistent trend. Further, under transient conditions this rpm changeover point can delay by several hundred rpm.

Now, if I can get my boost problem sorted, I might be able to delve further.

For the moment, the above explanation might explain one aspect that has been eluding me.

 

From settings page 7 on FC-Tweak or PFC Connect, you can see that the PFC can be set to start controlling the waste gate at specific engine speeds for specific TPS ranges. The wastegate operation on the PFC is quite simple. Once the RPM setting for the particular TPS% is reached, the PFC controls the WG solenoid in closed loop feedback from the MAP sensor to achieve the target boost level. For faster convergence, you can optimize the 'head starting' duty values. It starts with the specified working WG solenoid duty cycle and from thereon modifies the duty cycle until boost converges to the set target boost value.

 

It annoys me when someone posts about a problem, posts go back and forward, lots of good suggestions, then you never hear about the outcome. Here goes my non-resolution:

Thanks for all those suggestions about sorting the boost issue. I ran through them all and much more taking special note of:
I reached the point where my next diagnostic step was open up the turbo manifold. Working in the confines around the stock engine bay was giving me the ***** so, Eff it! I pulled the motor.

I removed the inlet section containing the charge control actuator to give it a thorough test. I didn’t spot it for some time but hidden from view when assembled, one of the viton hoses that I had installed last year had split at the nipple:



I have posted about hose tear resistance back in the 3rd Generation Specific section to progress that conversation there.

A pressure leak at the rupture would mean that there is no pressure holding the charge relief valve shut at the ~4300rpm transition point. (A note in passing. The throttle is being held full open, the TPS reading constant at 4.32V and the transition point setting is for 60% is 4080 rpm. Is the PFC delaying transition on account of not reaching the boost target?)


The ruptured hose and charge relief diagnosis was consistent with the symptoms. Not so definite was the effect on the charge control actuator. I could only assume that enough residual pressure remained in the ruptured line to allow the charge control actuator to at least crack open, dumping the primary boost back to a bit over 3 psi.

Therein was another lesson learnt in passing. I had smoke tested for boost leaks. Not having anything handy to plug the secondary turbo inlet, I injected the smoke into the flexible pipe before the intercooler, missing the ruptured hose.

The valves and seats in the exhaust manifold were all in good order and an in-situ check of solenoid valves and actuators did not bring up any further problems. So, I put it all back together expecting great things.

There was no improvement, not even a little bit. Boost curves before and after are identical.

Bugger.

I now have lots of other, non-FD things that need seeing to, so I have a while to contemplate my next move. Options include:

· Reinstall the stock ECU to see if any faults have arisen since it was previously used.

· Smoke test the full inlet track.

· Replace the wastegate, precontrol, and turbo control solenoids, regardless of them testing OK.

· Replace vacuum & pressure hoses again, just in case. (I’m done with viton and silicon and am considering other options.)

· Start tapping into pressure and vacuum lines and data logging pressures.

· Out of interest, test the charge control actuator at various differential pressures to see just when it cracks open.

· Pull the black box apart and individually test all components (again)

All further suggestions will be considered. Long term, I am going single turbo but in the mean time I don’t want to be beaten by this problem.