Fluctuating boost pressure
 

Ever since I replaced my stock y-pipe with an Efini y-pipe, I have had problem with fluctuating boost pressure above 5000rpm.
The twins are replaced stock ones.

A few weeks ago I started to get fluctuating boost pressure when WOT at low rpms aswell. I have replaced almost all vacuum hoses under the UIM; some were swollen and one were torn. But new hoses didn't help.

Transition works perfect, like before.

I will have to check the compression side for leaks, and check the pre control solenoid and valve.

Anything else that I should check?

Running PFC, 550/1300cc injectors, Supra fuel pump, 3" DP, Amemiya sports cat, mild street port, Twin Power, V-mount.

I'm think I have a problem with the Charge Control Actuator. Read this in another thread, and I have made the same observation.

I've done some more troubleshooting.
Wide open throttle to 5500rpm at idle doesn't give me any boost.
Checked Charge Control Actuator and Turbo Pre Control Actuator with Key On Key Off, but none of them moved.
Released vacuum hose from Charge Control Actuator, and it stayed open (rod extended).
Connected my boost gauge to the Charge Control Actuator and took it for a spin. 0 bar up to 4500rpm and then I read boost at the gauge.

So, the butterfly valve stays open during the whole rev register, dumping boost from the primary turbo via the Charge Relief Valve.

The troubleshooting continues... :)

I have replaced almost all vacuum lines.

when you take vacuum hose off the Charge control actuator, you should hear air being sucked into the hose. It gets it's vacuum from the vacuum chamber. The vacuum chamber gets it's vacuum from a hose running to the upper inlet manifold via a one way check valve (so that the vacuum doesn't get lost).

could be a number of things,

one way check valve to vacuum chamber,
vacuum chamber itself,
pipes to/from vacuum chamber,

a pressure/vacuum tester is a must if you have a sequential setup :nod:

Yeah, too bad that I sold my swedish made vaccum pump, it could have been handy now. :P

Checked Charge Control Actuator and Turbo Pre Control Actuator with Key On Key Off, but none of them moved.

PFC doesn't support this dagnostic method.Also,if you see the needle of the boost gauge fluctuating but the car feels ok,connect the boost gauge hose to another place,eg to the map sensor with a T and see if it changes anything.

That came to my mind that the PFC may not support that method, but did the test anyway. :)

I found one of the hoses to the Charge Control soleiond was torn (I replaced that one a few weeks ago). I also replaced the vacuum chamber.
0-4500rpm is better now, and I can see the Charge Control Actuator moving with key on key off.

Now the problem is that injection duty never exceeds 50%, and I have some bad popping sound from the exhaust above 4500rpm.
Listen to this video clip.

I have done some more testing.

I replaced the spark plugs and cleaned all ground points, including replacing the OEM ground point on the firewall with a new cable shoe.

If I remove the hose from the charge relief valve/actuator, I can hear air entering the hose. So vacuum is fine.

If I remove the hose from the pressure tank, I can hear the pressure be released.

I then connected my boost gauge between the outlet from the turbo pre-control solenoid and the actuator. The result was a shaky boost between 0.3 and 0.4 bar below 4500rpm (I guess that the ECU is duty controlling the actuator via the solenoid for prespooling the secondary turbo), ad above 4500rpm the reading was solid 0.9bar.


I then did the same to the turbo control solenoid, just like in this diagram:

Attachment 725003

The result was 0bar below 4500rpm, and -0.4 bar (vacuum) above 4500rpm.


So, the charge control solenoid, turbo pre-control solenoid and turbo control solenoids are all working as they should.

Still to test are the charge relief solenoid and the wastegate solenoid. Plus checking the actuators.

I have full boost during the whole register, but the engine power is a bit weak with some hesitation and a "drumming" sound from the exhaust system.

Vacuum at idle is good, battery is fully charged, gas tank filled up recently.

Had that issue years ago , did the non-seq mod set at 10psi ,I never had a problem since ......just my advice.

Terrible advice. Don't go non sequential. As soon as you understand how the turbo control system works its easy. Going non sequential is for the defeated :) you're making some good strides. You'll figure it out soon enough.

I would be a rich man if i had £1 for every time someone told me to do this/ go single turbo when i was trying to troubleshoot my sequential turbo issues.

One of the factors i wanted an RX-7 was for the sequential twin turbo, and advice like this is quite frankly, Pants. :dragster: :)

So is your current issue still that you're only getting about 50% injector duty?

do you have larger capacity injectors?

Yeah, when the sequential system works, it's awesome! :)

I haven't tried reving past 5000rpm at boost, since I have the lack of power and drumming in the exhaust.
I get some kind of hesitation around 3000-3500prm, then the power is good to transition, and then the lack of power and drumming starts.

I have replaced my RE-Amemiya midpipe with a RE-Amemiya sports cat, and after that the problems started. I have also tried with the stock cat, with the same result. Gonna put back the midpipe, and see what happens.
Also gonna replace the trailing ignition colis, as I have a spare set. No spare leading coli tough.

Again that's just something I did and worked , kinda like when all else fails type of thing and I'm sure more than half would agree . Its just another option no need to be upset about. Good luck by the way

Did a test of the turbo control pressure solenoid, and it seems to be working fine as well. Pressure is released fast when coasting down to 3000rpm.

So have you fixed your boost issue and now have fueling issues?

Leading ignition coil was bad. Will report back when it's been replaced.

Turned out to be the HKS Twin Power ignition amplifier that was. Bought it two years ago.
I threw away the twin power and bought a pair of MSD ignition coils with built in igniters for my leading plugs. Now she runs great again.

The MSD ignition coils failed a few months ago, so I replaced them with stock leading coils and a HKS Twin Power again. After that replacement the misfire was gone.

Though I still have problem with fluctuating boost pressure once the secondary turbo is engaged. I replaced the turbos last year with N3C1 turbos. I think my old was N3A1 turbos.

I have checked the wastegate solenoid and it can hold pressure.

The pressure tank doesn't hold pressure when it's connected to the engine's vacuum lines. If I remove the tank and connect a MityVac it holds pressure for hours. I guess that the Turbo Control Solenoid is leaking. Will check it later.

Attached are two diagrams from my PFC Commander. The first one is from third gear and the second one is from second gear.

I've got another wastegate solenoid that I will test, just to be sure it's not stuck.

There's some oil in the vacuum lines from the primary turbo to the actuators. Can the membranes in the actuators get destroyed by too much oil? There was also a little oil in the pressure tank.

Running PFC, 550/1300cc injectors, Supra fuel pump, 3" DP, Amemiya sports cat, mild street port, HKS Twin Power, V-mount.

The pressure chamber problem is now solved. I did hook up the MityVac to the hose from the pressure chamber to port a on the turbo control (pressure) solenoid and I could hear a leak.
I removed the manifold, the ignition coils and removed the solenoid, and found out that the hose was torn.

I don't think that this will solve my fluctuation problem, but I will give it a test tomorrow. I have read that the pressure tank can be removed, all it does it help for a quicker transition.

That's a long time from 2012 to 2016'to have this same issue.

Indeed.
I have lived with the problem since the car runs quite fine with uneven boost.

I know that the pressure tank held pressure last year and the boost fluctuated that time as well, so I don't think this is the fix.

Thanks for keeping us updated, always good

Today I replaced the wastegate solenoid and took her for a spin, but unfortunately the problem persists.

I also connected my boost gauge between the wastegate actuator and the wastegate solenoid and got the following result. Not sure how to analyze the readings from the boost gauge though.

replace all solenoids.

And vacuum lines.

6 years... lol

I lost patience after three failures in three years ;)

I suspect that your boost fluctuation may be your wastegate being overwhelmed. Porting the wastegate (so it can open wider) on your turbos may solve your problem.

The wastegate is ported.
I'm gonna tee in to the charge relief valve and see the operation from the solenoid.
Or maybe there's something going on in the butterfly valve causing pulsing boost from the secondary.

I did a test of the Charge Relief Solenoid. Teed in to the vacuum line to the Charge Relief Valve. Operation seems ok; vacuum until 4500rpm and then pressure. Boost fluctuates after transition att 4500rpm. Max boost 0.67bar (9.7psi). The troubleshooting goes on... :)

I pressure tested the wastegate actuator and it started to move at around 8-9 psi and opened more and more until I reached 14 psi, and it held the pressure.

I also found some oil spray around the gasket between the y-pipe and the crosspipe so I'm gonna replace that one.

Some more testing...

I connected my boost gauge to the charge control actuator and it behaves just like it should; vacuum until 4500rpm followed by pressure. Once the revs goes below 3000rpm vacuum is applied.

PFC Boost settings:

Pr 0.75 kg/cm^2 59%
Sc 0.75 kg/cm^2 68%


I then connected the gauge to the outlet from the secondary turbo. The vacuum/pressure line goes from the y-pipe to the upper intake manifold and then to the charge relief solenoid and charge control solenoid. I can see that the boost pressure from the secondary turbo is above 1.0 bar/14 psi (and bounces). At the Commander the boost pressure is approximately 0.75 bar/10.5 psi. So I guess that I have a boost leak somewhere as I don't think that it's normal that I loose 0.25 bar / 3.5 psi between the turbo and the intake.

I found this old thread with the exact same problem. I have searched and read so many threads and finally found this one. I'm gonna see if I can get another PFC.

PFC-Datalogit Wierd Boost Control Prob - RX7Club.com

The operation of the turbo control pressure side is all ok. So either PFC problem or maybe the map sensor is faulty?

You need a Datalogit to take logs and troubleshoot. It is not optional. You MUST know how the boost control solenoids and actuator controls or switching. Or take it to a shop.

I'm on vacation for another couple weeks but don't waste your time with commander for this

Yeah, I will take it to my tuner next weekend and do some logging. I will probably go non-sequentiall also.
Gonna replace the WG solenoid with a Mac one.

***** Problem solved *****

Finally the problem is solved. I went to the tuner with another PFC. We swapped them and the fluctuation was gone.

I also did test poor man's non-sequential, but the gain at the middle range was not that much and the loss at low range were too much (green and blue are non-seq, red is seq in the graph). So I'll stick with the sequential until it starts rain single turbos from the sky. :)

I bought a MAC 3-way valve to replace the stock wastegate solenoid. The transition was quicker and the boost more stable.
I think I will replace the PC solenoid as well.

At 0.9 bar I got 375 hp in the engine and 325 hp at the wheels.

Dotted line is boost.