3rd Generation Specific (1993-2002) 1993-2002 Discussion including performance modifications and Technical Support Sections.

Fluctuating boost pressure

Old 06-25-12, 01:52 PM
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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.
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Old 06-27-12, 04:44 PM
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I'm think I have a problem with the Charge Control Actuator. Read this in another thread, and I have made the same observation.

A simple test for the Charge Control Actuator is to start the engine and let it idle, the actuator rod will be pulled in. Stop the engine and remove the hose from Chamber A and the actuator rod will be out.

When I performed this test, as soon as I turned off the car, the rod was already out as if the car were turned off. So there has to be a leak somewhere right? I just dont know where to start with this?
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Old 07-04-12, 12:12 PM
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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.
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Old 07-04-12, 01:03 PM
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Originally Posted by Macen View Post
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
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Old 07-04-12, 01:18 PM
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Yeah, too bad that I sold my swedish made vaccum pump, it could have been handy now. :P
Attached Thumbnails Fluctuating boost pressure-austin-powers%2520penis%2520pump.jpg  
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Old 07-04-12, 01:40 PM
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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.
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Old 07-04-12, 01:44 PM
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That came to my mind that the PFC may not support that method, but did the test anyway.
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Old 07-15-12, 06:07 AM
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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.

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Old 07-18-12, 03:33 PM
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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:

Name:  turbocontrolsolenoidtest.jpg
Views: 267
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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.
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Old 07-18-12, 04:07 PM
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Had that issue years ago , did the non-seq mod set at 10psi ,I never had a problem since ......just my advice.
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Old 07-18-12, 04:40 PM
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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.
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Old 07-19-12, 10:35 AM
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Originally Posted by era1oner View Post
Had that issue years ago , did the non-seq mod set at 10psi ,I never had a problem since ......just my advice.
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.
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Old 07-19-12, 10:41 AM
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So is your current issue still that you're only getting about 50% injector duty?

do you have larger capacity injectors?
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Old 07-19-12, 10:41 AM
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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.
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Old 07-19-12, 03:23 PM
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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
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Old 07-20-12, 03:38 AM
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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.

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Old 07-20-12, 11:58 AM
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So have you fixed your boost issue and now have fueling issues?
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Old 07-21-12, 10:41 AM
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Leading ignition coil was bad. Will report back when it's been replaced.
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Old 07-31-12, 02:16 PM
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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.

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Old 08-19-16, 10:37 AM
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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.
Attached Thumbnails Fluctuating boost pressure-image1.jpeg   Fluctuating boost pressure-image2.jpeg  

Last edited by Macen; 08-19-16 at 10:42 AM.
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Old 08-19-16, 02:37 PM
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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.

Last edited by Macen; 08-19-16 at 02:40 PM.
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Old 08-19-16, 02:55 PM
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That's a long time from 2012 to 2016'to have this same issue.
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Old 08-19-16, 03:33 PM
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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.
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Old 08-19-16, 04:43 PM
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Originally Posted by Macen View Post
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
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Old 08-20-16, 03:09 PM
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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.


Last edited by Macen; 08-20-16 at 03:12 PM.
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