I've got an intermittent boost problem I was hoping someone could help be out with. I am running factory twins with the rats nest (lines redone) intact. It is on a fresh rebuild that I did last summer.

Sometimes the boost works wonderfully and pulls a perfect - 10-8-10 sequence. Other times the secondary has trouble coming on. It'll run something along the lines of 10-8-5. In secondary RPM range (5k plus) if I let off the throttle briefly when it does this and then get back on the boost jumps from 5 to 10 psi like it should.

Sounds like a sticky solenoid or actuator but if anyone has any ideas with where to start it would be greatly appreciated. This is currently the only gremlin on the vehicle and it's lack of consistent boosting is annoying.

 

Sounds like the vacuum chamber one way check valve is a little wonky. This one-way check valve can start to leak after a while, causing loss of vacuum to various controls when under boost for a while. A way to troubleshoot this one-way valve leaking is to note a gradual loss of boost and then drop the throttle long enough for your boost gauge to indicate at least 20 inHg of vacuum then slam the throttle back down again. If boost is back up to what it should be, then replace this one-way check valve. Basically what this test does is "recharge" the vacuum chamber when you let off the gas, allowing actuators to operate properly while the vacuum is still present. Most folks on the forum replace the stock Mazda check valve with a Viton one.

 

If you need the Viton check valves, send me a PM.

I had a sticky turbo control solenoid once that did a similar thing. Since it's only some times like this I'm thinking either a bad check valve so you don't have enough pressure or vacuum to actuate or a sticking solenoid.

You can T your boost controller into the output on the various turbo control solenoids and watch what they do. That's the best way to find a sticking solenoid so you can trace it down to one in particular. It's most likely one related to the turbo control actuator so that's only 2 solenoids, one that does pressure and one that does vacuum.

Dale

 

Let me point out that 4 turbo solenoids from Ray Crowe and a set of viton check valves is under 300 dollars total. When you think about it, there's really no reason not to replace all of that if you're going to have new vacuum lines too. The stock solenoids don't last forever but if you buy new OEM ones they will last until you sell the car. Why spend time on diagnosing individual ones when you can just replace it all for so little?

 

You most likely have a leaking vacuum chamber or check valve. What happens is when you let off the throttle the motor falls into vacuum and it will store enough to operate the system.

 

My fd did this exact same thing when I bought it years ago as you described. My issue was a loose upper Y pipe coupling. During boost transition, the added air volume from the secondary coming on line would further expand the coupling and slightly lift it to leak boost (10-8-5) but, when you get off the throttle and floor it again, the sudden rush of air from both turbos forces the coupling to push up really quickly and top it out against the upper flange lip to make a better seal. I tightened up those worm clamps and never had the problem return.

 

OK, so I let the car cool down for 3-4 hours while I did some school work. After that I re-init it again and turned the key off then back on. I started the car and let it go through the full 10/10/10 minute cycles. Took the car out from there and everything is fine. No stumble under boost, no blipping issues like I had before, and vacuum is a bit higher at idle than the previous map.

The only changes I made for that map were-

-Disabled the O2 feedback
-Set fans to 85C in all three categories

Not sure if it was due to the 02 sensor setting, or if making the car learn when it was already warm, BUT I recommend that you go through the learning process with a cold car so you get a full 10 minutes without ANY electrical loading (i.e. fans kicking on).

Thanks for the help everyone, still learning a bit!

Joe