I've been tinkering with this for a while now, but I can't seem to figure it out.

I've checked all my vacume lines, and I can't seem to find any problems.

I did find that my turbo control solenoid was slowly leaking on pressure side (https://www.rx7club.com/3rd-generation-specific-1993-2002-16/how-much-emissions-can-i-eliminate-without-pfc-919955/) and I thought for sure that was the problem, but after replacing it, there is no change. I'm still not getting the second turbo up to 10psi.

I don't know where to go from here. Can anyone help point me in the right direction?

My car is almost completely stock, I can't find a vacuum leak, and the turbo control system seems to be working from what I can tell. It boosts to at least 10psi until, 4500 rpm, then it clearly bounces and hesitates at 8psi before dropping down to 5 psi.

This is really disappointing and frustrating because from what everyone says the fun really starts when the second turbo kicks in, and I'm not experiencing that yet.

 

My experience is that faulty check valves will create secondary boost issues. Dale Clark has some good check valves that are not too expensive. I suggest that you replace all of them.

 

I've already got some of Dale's valves. I checked all of them when I was checking vacuum lines and didn't find any problems.

Thanks though.

 

Another possibility is a clogged cat or precat.

 

or the other 100 things it could be....in my experience, start from the turbos and work your way to the engine via turbo/intercooler piping...usually a leak somewere. Mine happened to be the nuts that worked their way off the secondary turbo outlet to y-pipe causing a 1/8" gap for boosted air to leak from

 

With 10 psi on the primary, a leak is unlikely.

 

This
and this

 

i had the same symptoms as the op....10-8-5 and it was due to the nuts working their way off the secondary turbo outlet to y-pipe. Thats why i suggest starting at the turbos

 

Check that the pre-control and wastegate soleniod connectors aren't swapped over.
I had the same symptoms as you (10-8-5), and they were indeed swapped over (the shop that did the rebuild for the previous owner must have done it). Swapped em back and it was like a different car!

Thread/details here: https://www.rx7club.com/3rd-generation-specific-1993-2002-16/swapped-wastegate-turbo-precontrol-connectors-858203/

 

Wouldn't a clogged exhaust affect both turbos?

I get 10-8-5 like clockwork. I actually bounce a little over 10psi early on in the RPM's, but once I get past 4500 RPM, it stops at exactly 5psi almost as if it's electronically or mechanically limited.

It's strange, because my car really has no mods, its only got 60K miles, and that I know of, its never really been torn apart.

 

Not really. The primary turbo spool so fast and lower exhaust gasses at lower RPMS that by the time the exhaust is filled with gasses the secondary is past it transition point. Reason it goes up the it decreases. On a really bad case, then yes but I would guess your engine would die. Same case as a banana in the tail pipe thing.

 

At 10 psi on the primary, you are at low rpm, and you have relatively low flow thru the cat. Once the secondary turbo kicks in, rpms are much higher, and flow is increased.

An example would be blowing thru a straw. If you only blow a little bit, its easy. Try to blow a bunch of air thru a straw, and it won't (can't) accommodate the extra air. If your cat is clogged, it wont allow a large amount of air to pass thru it.

 

Wouldn't a clogged cat show a progressive drop in boost as RPMs increase? It isn't like the amount of exhaust magically doubles when the second turbo kicks in.
A sudden drop from 8->5psi seems to indicate a control issue rather than a physical restriction.

dagoof, did you recently buy the car, and it has always had this issue? Have you previously had it running a normal 10-8-10 (ish) pattern?

 

One of my previous FD had a clogged cat when I bought it. It would go 10-8-4.

 

If this were my car I would remove the cat and precat (assuming it has one). I would install a down pipe. I would then take the main cat and try to shake all the loose pieces out of it. This can take some time (experience talking). If you are able to get much to come out, it should function well for quite a while.

Precats seem to be more prone to clogging than the main cats. If your precat is clogged, the main cat may still be pretty good.

 

wow, i think my car is suffering the same fate as this.

 

If both turbo control solenoids have been changed, then it may be a clogged cat. Its hard to tell if its the cat, even if it has the element still in there. Best way is to throw in a straight pipe or known good cat. I had the same problem on my first fd and it was the main cat being clogged.

 

If not a clogged cat, then another place to look for laggy secondary boost is the CCV on the y-pipe.

Petite Racing has one that helps with this. "lazy secondary turbo, these valves often have shaft bushing wear making them sticky and causing the secondary turbo to be lazy and in worst case scenarios even dumping boost off."

http://shop.pettitracing.com/pettit_.../i-408827.aspx

They seem to have these in stock now, but $200 clams is a bit pricey

But, removing the one you have and cleaning/lubing it might help too. Chances are this is the problem, surprised no one mentioned it yet.

Good luck and report back... with PICS!