WaLieN

Well, ever since the downpipe was installed (had to remove the turbos due to a REALLY stuck stud (had to get it lasered out by a machine shop), the boost has been kinda iffy. If I let the vaccum build up a little, the car will boost just fine. But say if I were getting on an onramp behind someone, at 0psi and 0in/hg, sometimes it won't boost at anything more than 2psi. This also doesn't happen *all* the time.

I know it can't be the vaccum chamber, as it was fine before the install (the car was boosting just fine). Before I tear into things and replace random check valves and couplers, can you guys tell me what it *might* be? I was thinking it might be the coupler above the y-pipe or possibly the clamp itself. What do you guys think?

Herblenny

iTrader: (13)

I think if its the coupler issue, you would see it all the time.. I don't think that kind of leak will cause random boost issue..

I also don't think its your vaccum leak since that will cause your boost to be off all the time or usual secondary issue.. But sounds like your primary isn't kicking in..

If I have to make some sort of guess, I would say it might be your solenoids.. either the connection is bad or its coming on and off due to vibration or something.. I would check all of your connectors to make sure they are securely clipped on..

I had so many issues with seq. set up.. and finally when I got it running perfect, I have now have coolant issue..

Good luck!

speeddemon7

im having the same issues right now.Quick question.
Did you reuse the old downpipe gasket or did you install a new one?

cruiser

I'm almost sure its the one-way check valve on the line going off the vacuum chamber towards the UIM. Check that first.

If its leaking you loose your vacuum needed for all sorts of operations with solenoids.

WaLieN

Do you have a picture of that check valve's location? To test it, do I just blow into one end?

WaLieN

Ttt

WaLieN

Now I am thinking it might be a boost leak, since the boost breaks up at 6,000rpm+ and starts to fluctuate between 6 and 9 PSI. I guess I will be doing some coupler/hose clamp replacements.

wrankin

Check your pressure levels at both the vac and pressure tanks by teeing off the feeds. They're not hard to get to and it beats trying to debug the whole rats nest.

-bill

luizajeff

I'd say double check all the vac lines that plug into the turbos but I was having slow initial boosting on my car until I installed Hallman's RX Pro MBC's (2) and I bypassed the solenoids all together - and now they spool very quickly!

spooledUP7

The Hallman is simply a manual boost controller and has little to do with the Sequential acutation (unless you have the boost set below 7 psi).

I am going to go with the Solenoid guess. I speak out of experience and I my guess is the TCA vacuum side is the suspect of failure. If you have a second boost gauge, you can tee into the vacuum line to the TCA and watch for vacuum just before 4500 rpm, and it will hold until under 3000 rpm. Anything other than this and it is not working properly.
You can also test the pressure side of the TCA in the same manner, but it will be boost rather than vacuum you are looking for.

The check valve is of course the easiest thing to check, so do this first and except no leak-downs.

WaLieN

What exactally would I test for?

I reused my old DP gasket, but it was in very good condition. I just wire brushed it a little, and threw it back in.

BTW, I rechecked all of my couplers and replaced all of the hose clamps. The problem is still there. It seems that the problem only occurs after ~3,500rpm (when the turbo transitions to the 2nd turbo). If I boost at 2,500RPM->redline, I get solid boost in that gear (but sometimes it still breaks up from 6-9psi at high rpm). Then if I shift it, it can only boost at 2psi max. If I change gears, and lay off the throttle, it boosts normally again. This thing is giving me a headache.

I still haven't re-torqued my DP nuts, could an exhaust leak at the DP cause something like this?

WaLieN

Oh yeah, to test the two solenoids, can I simply unplug them?

WaLieN

Anyone?

speeddemon7

I think you can unplugg them and you should still see 7 psi of boost.if you dont hten you have a boost leak somewhere.I could be wrong though.Also try switching electrical plugsd and see if your problem is fixed or if it changed somehow.It may let you know if you have a problem with your solenoid.

WaLieN

I checked all of the connections on the solenoids, and they were fine. I also checked all of the check valves, they were also fine. I did replace some old vaccum hoses and found that the boost side of the TCA hose at the rats nest was disconnected, so I fixed that. Well, now the car boosts fine at any RPM in a single gear, but if I redline that gear, I only get 2psi on the next gear. Could it still be a solenoid problem? Man, just when I thought I had it fixed -- it's not.

WaLieN

^^^

wrankin

sounds like you aren't building up pressure (or have a leak) in the pressure tank on top of the engine. the turbo control actuator used both pressure and vac to operate. get a tee fitting and reroute your boost gauge to measure boost/vac levels in this tank while driving.

alternately, it could be one of the two solenoids controlling the TCA.

good luck,

-bill

WaLieN

I think my pressure tank is fine; after I shut down the car, it releases air when I pull on of the lines off the pressure tank.

Could it be the actuator that is going out, or would it be the solenoids? Thanks for your continuing help.

kevinvr6

iTrader: (1)

i got the same problem, intermittent primary boost =P

WaLieN

That's cool, I guess.

https://www.rx7club.com/showthread.p...ighlight=boost

That is how I solved it.