Need suggestions for diagnosis if charge control valve is bad or if vacuum reservoir is contibuting to the problem. Intermittant problem on 93 FD with sequential twins. Sometimes transition from primary to secondary boost under WOT is sluggish. Sometimes boost being vented is audible for several seconds. Sometimes transition works OK. This sounds like the charge control valve is sticking or hung up, but if there is a small leak in the vacuum reservoir, it may also keep the valve from operating properly. Is there a way to diagnose this problem without removing the vacuum reservoir and charge control valve to examine them off the car? Both require substantial work to remove other engine components to access them. Any suggestions?
Ron A.

 

I'm having the same problem. Let me know if you find a solution. Mine seems to free up if I go and hammer on the car a bit at the transition point. It was getting really stupid at the last autocross of the season with my club, and it seemed to get freed up when i took it to an abandoned business park and hammered on it through the changeover for a good 15 minutes.

Before you go pulling everything apart, you might want to check that the actuator that controls the charge control valve (the wastegate actuator can) is still working, that the charge control valve is moving freely, and that the vacuum lines are good rather than dive into the rats' nest right away.

 

By process of elimination you can determine if you're leaking any vacuum.

Buy a tee fitting (I got them from McMaster-Carr), a spare vacuum gauge/boost gauge/mityac and several feet of vacuum tubing. Insert the tee in the hose to the vacuum chamber and run the line out the hood and into the cabin. I usually just leave the window cracked open. If the vacuum chamber or one of the components on that circuit is leaking, you'll see the vacuum steadily decrease when you're driving under steady load. (Highway driving without hills is ideal because it keeps the engine out of vacuum but doesn't actuate the solenoids and consume stored vacuum). If you're using a mityvac you can just pump it up with vacuum and watch for leaks.

If you verify vacuum is good, you can move the tee to the line between the CCV and CC solenoid. Run the car through boost transitions, and if you consistently see full vacuum or pressure (I forget which offhand) applied by the solenoid to the actuator the solenoid is good.

Also dont forget to use the Mityvac to verify there is no leak in the CCA.

Sticky CCVs are common and might the issue if the car passes the first two tests. The bushings in the butterfly valve wear and the extra friction causes it to move erratically. If you think this is the case, Pettit sells a rebuilt unit that has better bushings. I haven't used one but the solution is very sensible.

David

 

dgeesaman- good suggestion. I have a Mityvac and it never occurred to me to use it (duh). I was going to just order the rebuilt CCV from Pettit, but they are back ordered. Mazdatrix has them but at three times the price. I think I will diagnose first, instead of ripping parts out and replacing, like the dealer mechanics usually do.

 

I need to bring this thread back:

I've finally got some time to re-test my sequential setup. Been running non-sequential for testing purposes. I've been having issues for a long time with the sequentials not boosting past 5psi on the secondary, but it works fine when I went non-sequential.

So anyway, what I did was hooked up a boost gauge to both the CRV, and CCA solenoids output port.

What I found is that both solenoids are only outputting vacuum all the time. As far as I know, both solenoids should be switching to pressure at the 4500rpm transition in order to open the CCA. and close the CRV. But they're not, they're both only sending vacuum all the time. I did notice just one time, the solenoid for the CCA very quickly released the vacuum at about 5500rpm, and then right away went back to full vacuum.

I've tested the solenoids many times, and they're all working to spec when powered/not powered. And I also hooked up the gauges prior to the solenoids, and the lines are getting pressure as they should.

So I was wondering what you guys think it might be? Could it be a wiring problem? I have a powerfc, but that ECU is not the issue as I've switched it back to the stock ECU and I have the same problems, as well as with another powerfc that I had before this one. Thanks!