Here's my setup:
- Stock turbos
- Ported wastegate
- Apexi PFC + commander
- V-mount
- Trust Airinx dual filters

Since a year ago I have started to get lower and lower boost. Currently it's at ~4.5 psi before transition and ~7 psi after. The filter at the primary turbo is leaking some oil so I guess that the primary turbo is leaking. There's not much oil in the intake pipes or intercooler.

I guess that the only way to be sure is to remove the nuclear reactor turbos and check for leaks and play.

On the last autox I almost beat my old record, so boost isn't everything.

 

https://www.rx7club.com/showthread.php?t=1068092

See if that helps.

 

check your pressure tanks and the vacuum lines going to them. had the same problem when i ran the twins sequential.

 

Last year I replaced the check valves with new ones from Dale Clark.

The pressure chamber is holding pressure over night, but I haven't checked the vacuum chamber or the solenoids. Guess I'll have to get a MityVac.

 

When my car would only do 8 psi it ended up being a couple of cooked vacuum lines but the main culprit was the chamber that was down and hard to access. The line coming off the nipple on the bottom had a pin hole in it. I replaced that line and had full boost back.

 

From Troubleshooting

"Primary air is supplied directly from the Primary Turbocharger compressor, no one-way check valves or pressure tanks. Note that the Primary Turbo must be operating and generating more than 7 psi of boost to be useful for any of the solenoids or actuators."

I've got 4.5 psi.

Today I tried plug the vacuum/pressure line from the primary turbocharger compressor to the wastegate actuator, in order to try to keep the wastegate door shut. But I still got 4.5 psi.
How will the wastegate door react if there is no pressure to the actuator? Will the actuator spring keep the door shut, or will the exhaust gases push the door open?

 

The wastegate actuator needs pressure in order for the wastegate door to open. So with low boost the wastegate door won't open.

Unfortunately a major leak in the wastegate or precontrol actuators can cause major overboost and engine damage.

David

 

Yeah, I'm aware that I may overboost causing a leak. But I just wanted to make sure that the wastegate door was shut.
What if there is a big crack around the wastegate door. That would make the boost stay low, right?
Can it be a bad charge control valve leaking compressed air through the air filter? Or a bad pre spool door leaking too much exhaust from primary into the secondary turbo?
Or maybe a bad primary turbo?

 

No need to jump to big diagnostic conclusions. Much more likely to be a bad solenoid, actuator, vacuum line, check valve, or vacuum tank.

 

I would start with looking for boost leaks. That's hands down the most common source of low boost.

Also, old/bad plugs can do funny things.

Dale

 

So over a year ago you started having a boost problem and have not tried resolving it until now where it's at 4psi?

Why not check your couplers and big connections first? If you had a noticeable drop suddenly I'd point to that.

 

I use my car only at track. Last year I got my first child, and only had time to do one trackday. Now I've got time to take a look at the boost problem.

It doesn't sound like a boost leak. I have had a boost leak on the cross over pipe before, so I know that high frequent sound.

I'm gonna order new plugs and replace the fuel filter. Also gonna check the vacuum tank. The pressure tank is holding pressure (removed the hose and heard a swoosh).

"0 to 3,000 RPM
In this RPM range, boost is produced by the Primary Turbocharger only. At this time, most of the the exhaust is directed to the Primary Turbo by the Turbo Control, and the Secondary Compressor is isolated from the Primary by the Charge Control. Boost pressure is mostly regulated by the Turbo Pre-Control.

3,000 to 4,500 RPM
In this RPM range the Turbo Pre-Control valve is almost fully opened and preliminary rotation of the Secondary Turbo has begun, any boost pressure from the Secondary Turbo is vented via the Charge Releif Valve to the air cleaner. Boost pressure is regulated by the Turbo Pre-Control and the Wastegate Control.

From the above description, there is not much happening when only the Primary Turbocharger is operating. However, at 4,500 RPM when the change over occurs, lots of solenoids and actuators are changing operation. This is when most of the problems occur."

So it could be a bad pre-control valve, solenoid or actuator.

 

Even if they check out "good" with a Mitivac, replace the check valves. I hunted for months trying to find a turbo problem, tested the check valves several times. Finally, I replace the check valves (cause they were cheap from Dale). Problem solved. Just replace your 20 year old check valves, buy some new ones from Dale.

 

I replaced all check valves a few years ago with Dale's white semi transparent ones.

 

Today I tested the vacuum chamber; all ok.

I also tested the pree spool and wastegate actuator with a pressure pump. The actuators held 15 psi and the arms were moving.

When I removed the vacuum line to the wastegate the hose were dripping oil. There was also oil in the line on the pressure side from the primary compressor to the wastegate actuator.

Maybe the primary turbo is toast. But if it is, shouldn't there be more oil in the IC and pressure pipes then?

Since I only have 4-5 psi of boost from primary turbo, the wastegate won't open. So why am I not getting higher boost? I have checked all couplers.

I'm gonna insert my boost gauge on the compressor side of the primary turbo and compare the boost there to the boost in the intake manifold (via the Commander).

 

Today I cleaned the wastegate and pree spool actuators from some oil.
I also checked the boost pressure at the primary turbo compressor, and it was the same as in the manifold (4.5psi).
I pressurised the wastegate actuator and the arm started moving at 7 psi. So the wastegate should be closed at 4.5psi.

Next will be to remove the downpipe and check the status of the wastegate flap. If there's no cracks around the wastegate, the next thing will be to remove the turbos.

 

Pressure test the system. Some boost leaks don't make any noise. Had a friend with weird low boost, pressure tested the system and found the vacuum cap on the deleted AWS had come off. It was a small hole but lost a LOT of boost.

Remove the filters and use plastic bags and hose clamps to seal the intake. Set an air compressor to about 15 psi and hook the hose up to a pre-throttle body nipple, like the Y-pipe nipples. Look, listen, and feel. You'd be surprised what can leak boost.

Hands down that is the most common problem with boost issues.

Dale

 

I guess I have found the source of the problem
It explains why the boost decreased over time, the crack probably got bigger and bigger.

A tip when doing a pressure test is to remove the vacuum hose to the charge relieve valve, because there is still vacuum in that line when the engine is off and the valve will "leak" when there's vacuum.

 

Well done