tsmysak1

I hope to tear into this tomorrow. I have this worsening condition. Car used to boost 10-8-11....Now it is sort of a dismal 10-7-8

Mods are a downpipe and manual boost controller (and a driver that is getting more interested in going faster).

Strong boost through 4500, but falls to a 7 psi and stays pretty much there with an occassion 10 psi above 4500 rpm when passing or from some highway speed. I can almost never get it to recover to 10 psi by letting off and re-tromping.

Boost is normal under 4500 rpm. Spools very quick. I do see 10 psi on the secondary occasionally, which tells me the turbo is not shot. No real visable smoke of any kind. I have started to check solenoids and lines. I have recently done a silicon hose job and double checked it.

Car also used to spike at transition when I closed the pre-spool valve controller, but now, I can close it all the way and there is no spike or any real improvement on the secondary.

I am thinking something is messed up between the boost control valve and the secondary compressor outlet, like a leak. Does this sound right? If there is a boost leak, then this would drop the boost level above the transition point. Please confirm.

I would also like to know if this control valve opens up before or after the prespool on the secondary. Gurus please help!!

seanbrowning

Sounds like a vacuum leak. But maybe rear turbo giving out? Is it leaking any oil?

NeedFD

what's the length of the mbc hoses? also did you check that they were secured and zip tied?

WaLieN

A lagging secondary turbo could be a multitude of things, but two primary things you want to check are a collapsing turbo hose (the elbow) and a clogged cat. These two things can restrict flow on each end, causing a huge restriction.

tsmysak1

Long...maybe 20 inches...I wondered if that could be a problem... I upsized the prespool hose with no effect.

What are you thinking? Please tell...

tsmysak1

Had the hose off and looked at it. Doesn't seem to be compromised, but it is not new by any means.

Changed the cat and no difference. I would assume that the cat would also effect the primary. This is distinctly a secondary problem, which is more like the hose.

adam c

iTrader: (2)

Since you get 10 psi at times on the secondary, you don't have a boost leak, and you don't have a bad turbo. If it were a bad cat, I don't think you would see 10 psi on the secondary either. This means that you probably have an actuator problem. I would start by replacing the check valves. Dale Clark has some inexpensive replacements. If that doesn't help, I would get rid of the needle valve (if it is a needle valve) on the prespool controller. Replace it with stock pill, or ball & spring controller. A needle valve on the prespool line doesn't work very well because of the long hose.

tsmysak1

I suspect this is a leak. There is no oil and it will boost 10 psi sometimes... I have no reason to suspect the turbo, but more like a leak... Suggestions?

tsmysak1

Replaced the check valves already. I only have one good pill and I can't remember which line it is for... I can do that though, because I think I could get some pills made...I will let you know how this works.

adam c

iTrader: (2)

The stock prespool pill should give you 8 psi at transition. The wastegate pill, if placed in the prespool line, will give you around 9 at transition. Either pill will be fine in that line. Just make sure that the line is stock length, which is about 4-6 inches.

dgeesaman

iTrader: (7)

Still start with looking for boost leaks. A minor leak can be intermittent, but they are one of the easier things to look for and a good inspection of these is always time well spent.

Dave

WaLieN

I'm sorry, I skimmed through your post and did not provide enoguh information.

Do what Dave says first. With all boost issues, you always want to inspect all of the piping that sees boost pressure.

Secondly, can you clarify on one of your symptoms?
So if you let go of the throttle for an unknown amount of time, it can recover to 10psi?

With a boost issue, it will be incredibly difficult to diagnose unless you can duplicate the problem. I had an issue with a turbo control solenoid that only acted up in a particular situation (once it passed the transition point, if you don't shift fast enough, the TCA will remain open causing low boost, but if you let go of the throttle and let it recover, it will be fine).

Try to duplicate the issue. Someone mentioned that it has to do with an actuator, I would agree somewhat. The actuators are really well built and I rarely hear of failures. You can check its operation with a handpump if you wish. What usually fails is the solenoids, which are difficult to diagnose since they react differently when hot on failing solenoids.

Since you said the prolem was intermittent (to your knowledge) and you have checked your check valves, I would really rule the intake hosing, pressure tank, vaccum tank, etc.
I really think it's something with your solenoid.

Do this: Start out in second gear w/ a WOT. Shift into third quickly and don't let the revs drop too much. In third, WOT it as well. Notice the boost in each RPM range. If the boost in third gear does not get to 10PSI, let the car slow down until ~2800RPM, then rev again to see if your boost will recover to 10PSI at all. I know this test sounds incredibly weird, but it will give you a good idea on what exactly your turbo system is doing.

Feel free to contact my directly on AIM if you have any questions. Good luck!

WaLieN

BTW, the following site will explain what goes on with the turbos: http://www.autosportracetech.com/RX-7/rx7stuff.htm

It helped me a lot when I needed to find out the function of each part of the sequential system.

tsmysak1

More clarificaiton...

I basically cannot get it to boost above 8 psi after the transition occurs.

No matter what I do, it will only boost 8. It is 10 psi in an instant on the primary and every thing seems normal until it hits the transition. I would say that the tranistion seems much lower than 8 - maybe 5 psi - and then it builds slower than when the primary spools.

There are no gushing sounds or anything like that. When the temperature is hot outside, the problem is worse (responds slower), but exactly the same type of behavior.

If it ever does go to 10 psi on the secondary, which is rare, the pattern is like this:

3000 - 10 psi
3500 - 10
4000 - 10
4500 - 6
5000 - 10
5500 - 7
6000 - 8
7000 - 8

ptrhahn

iTrader: (9)

Sounds more like a clogging main cat. How many miles on it?

The sequential system can be a little inconsistent anyway, depending on conditions, but your symptoms sound un-dramatic enough to indicate that it's just a little backup... similar to what you'd get if you went out and drove on the first unusually hot day of the year.

tsmysak1

It did boost 10-8-11 for a while. Then I don't know what changed....

I just replaced the cat with a 30K original OEM piece. Both the old and new bahved exactly the same.

ptrhahn

iTrader: (9)

I'd begin by checjing the vac and pressure tanks to make sure they hold well, then move to the various check valves to verify that they hold. Look for any crimpted, slit, or worn hoses along the way. Once all of that's verified, THEN move on to solonoids.

dgeesaman

iTrader: (7)

I agree with the others - once you rule out the possibility of boost leaks, then look for vacuum and pressure (check valves). Also look for loose hoses.

I would run the KOKO boost test next (http://www.fd3s.net/boost_test.html) and see that the CCA and TCA move consistently.

The results of this investigation should help narrow your focus if things indicate you have a bad solenoid.

Dave

tsmysak1

Vacuum tank tested... no leak.
Pressure tank tested...no leak

All check valves replaced with good aftermarket ones... no difference.

I have also done the hose job very carefully ....one hose at a time..

I am off to work on this thing some more and possibly test all the solenoids.

What a mystery!

adam c

iTrader: (2)

Did you change out the prespool line?

dgeesaman

iTrader: (7)

Well testing the solenoids is actually quite simple. You simply buy a plastic tee fitting and move your boost gauge to one of the lines between a solenoid and an actuator. If you take your time studying the diagram, it's not too difficult to test every actuator/solenoid in the system. Just tee it in there and look for the results.

1) CCA: look for 100% vacuum (15-20inHg) at 4500rpm.
2) TCA: look for 100% vacuum or 100% pressure beginning at 4500rpm. You can access these two right under the pressure chamber.
3) CRV: you should see full vacuum from around 3000 to no higher than 4500rpm. It may open sooner or close sooner depending on how fast you're accelerating.
4) Pressure tank: the first time you boost should charge the pressure chamber with 10psi, and when you transition to the secondary it will dip down for a moment. Then let off, and see if tank loses pressure while the engine is at idle (vacuum).
5) Vacuum tank: it should charge as soon as you start the car, and during boost the level will lower as it actuates the CCA, TCA, CRV, etc. But it should always have some pressure (say, more than 10-15inHg during the boost phase, and it should full recharge immediately when you let off to shift gears, etc).

The line that doesn't operate like I described above probably has the problem. Then you follow the line in each direction, testing the components until you find the one with the problem.

Dave

tsmysak1

Dave, thanks for that last post, I am going to use this for diagnostics anyway and go over everything with a fine tooth comb, just to make sure things are right.

So, I dug through my parts pile and found another secondary intake hose and it seemed a little stiffer than the one that was on the car, so I changed out that and the MBC line for the prespool. The pill that I still had was for the boost control, but it seemed logical to substitute this on the prespool for the sake of the check.

I noticed first that the restriction for the pill was much less than the MBC line with the valve. When I took it out for a drive, I got like a 8-6-8 pattern. Right pattern, wrong level.

I adjusted the boost level a long ways (closed) to bring the boost back to 10. Since I changed the weak hose and the MBC at the same time, I cannot say for sure, but I am betting that the prespool line was it. I am going to experiment some now, changing only one thing at a time to come up with a better setup.

This has been a great dialog. I really appreciate all the help...