3rd gear 2psi - all other gears ok
 

Hoping you guys could help me figure this out. Car was working fine 10-8-10. Replaced FPD and boost got all screwy - crossed a couple of lines. Fixed that. So now I'm getting good boost again in 1st, 2nd and 4th gears, but I'm only getting 2psi in 3rd gear.

If I nail it in 2nd, primary and secondary boost properly. However, when I shift to 3rd from the top of second boost only hits 2psi and stays there. 4th gear seems good. I can run it through 4th gear and get 10psi. But I'm not getting anything more than 2psi in 3rd.

Have checked and replaced all couplers and clamps. No leaks.
Vac lines have been checked against the diagram and appear to be fine.
Solenoids have been checked and seem to be working properly. Have also checked them on the PowerFC.
Actuators have been checked also.

Any ideas?

what about putting it in 3rd at like 20mph and going WOT...can u induce more boost at low rpms?

I don't know if this is useful, but I put together a page a while back after I spent all my time diagnosing my problems. I ended up discovering an intermittant turbo control solenoid.

http://www.millsisland.net/twiki/bin...TurboDiagnosis

You may find the Turbo Component Descriptions useful in working through your problem.

I'm interested in your answer to "teamstealths" question. If the turbos will transition in 3rd gear, it might narrow it down a bit.

Good luck. Turbo diagnosis sucks.

Rich

wow thats a tough one doesn't make sense...

yeah, its an odd one.

to answer teamstealth's question - yes, on the low end while on the primary i can get boost. if i'm in 4th for example at 2,500rpm and i hit it, i'll get full boost. i think it works in 3rd too. but if i run it through 2nd making good boost and hit 3rd gear, all i get is 2psi of boost.

whiteshadow - thanks. it sounds like we possibly had the same issue. i'm gonna check that stuff out.

if anyone else has any input, please keep posting. thanks.

How about starting in 3rd gear at 2500rpm and having the turbos transition?

Try out the 2500/3rd gear pull and let us know what happens. I suspect your turbo control actuator isn't switching over properly. In 4th gear, it's got enough time/pressure to push it open slowly so it works. In low gears, everything happens fast so the primary can dominate the boost pattern. 3rd gear is usually the worst culprit.

Start hooking your boost gauge up to different parts of the system and watch what's going on.

Have you read Derek Vanditmars page?

http://www.autosportracetech.com/RX-7/rx7stuff.htm

It's an excellent source for diagnosing some of this stuff.

As a caution, DON'T keep going into secondary boost if things aren't working properly on a day to day basis. If the TC door isn't opening properly, you can actually force boosted air back through the secondary turbo compressor, which fights against the limited exhaust airflow to the secondary and stresses the whole thing. This CAN'T be good for the secondary seals.

Rich

Can't actually drive it right now as its all apart :(

It was weird. I could accelerate through 1st and 2nd hitting 10psi then I'd shift to 3rd and get 2psi all the way through. Shift to 4th and full boost again. Couldn't get more than 2psi boost when I got on it in 3rd at 2500-+rpm, but I could get boost throughout 4th.

Looked at the actuator a little while ago that teamstealth pointed out and it had already been replaced at some point in its life also.

Its weird that the problem only shows itself in 3rd gear...

Already read through the autosportracetech site and most every post on this forum. The thing that sucks is that most people don't bother to update their threads letting us know WTF the fix was. I even tried contacting the people that have the threads open in the archives to see what their fix was and got no response.

If you stay WOT through 1st and into 2nd does the same problem occur. On one of mine if you didnt prespool sometimes I would only get 4-5lbs at WOT.

djseven - no.

I get good boost in every gear except 3rd. prespool works well except in 3rd... :(

Unfortunately, this is going to be real hard to diagnose until you get the car back together. Your best bet is going to be to hook one or more boost gauges up to various points of the system and watch what happens. Check the pressure and vacuum chambers first -- they're easy. They should hold vac/pressure for a LONG time after shutdown (hours). The TC solenoids would be my next choice. If the TC door isn't opening or staying open, you'll get CRAP for boost.

If you've got a mitivac, you can T into a few places and check some things prior to reassembly.

At one point, I was using my boost gauge, a spare boost gauge, and the PFC to measure different aspects of boost. Pretty amusing.

Good luck ... off to the track.

Rich