3rd Gen 1994 FD Boost Problems (as usual)
 

Having read most of the previous questions on the forum about boot problems, and the problem could fall within one of three. A faulty turbo control, disconnected or broken vacuum line or a faulty wastegate!

My problem started after driving back from work on Thursday night, were I set my Apexi AVCR to a 12.8 psi as I always had it set to this when driving over stock. Parked the car and turned the boost back to standard. Next day morning when I started the car, the pressure needle was jumping erratically up and down and after got the car warmed up, drove as normal but it doesn’t boost as normal anymore. Boost pressure kept going up and down.

When driving hard, can feel power and 1st turbo boosting but won’t go above 4 psi, then once reached over 4,500 RPM can feel 2nd turbo but rev goes crazy all way towards red line but also at the same time can feel loss of power.

After examining under the hood, I found the Y-coupler had been pushed up and almost came out of place. I took everything apart and clamped it back to place yesterday. Drove for like 20 minutes and felt normal and this time could get boost up to 8psi but then problem started again, however this time the Y-coupler is still intact.

Could any air leaks cause the a sudden over boost and for the revs to go so high suddenly as well as loss of power at the same time?

Your revs can't go shooting up without either spinning the tires or slipping the clutch. Since you say you feel a loss of power too I think your clutch is slipping.

Finding the loose y-pipe coupler is a good indication, but did you take it off the car and work thru it to look for cracks or splits? While you're at it, take off the other couplers around the intercooler, remove any metal shields from them, and look for cracks in those. Also check the pipes between the 2 stock blowoff valves and the turbo y-pipe.

The TCA, wastegate, and other stuff don't strike me as likely sources.

Dave

Yes, I took it completely off and cross checked it all over before putting it back on. I even uprated the clips and now use rally ones. I thought of the possibility of clutch slipping as well but I still can't justify the loss of boost and unable to gain over 4psi now.

Bearing in mind I eleminated the ECU from my turbo control and have tapped the top sections of the actutators and the boost now is completely controlled by the Apexi AVCR. Perhaps I should check the Apexi selonid and make sure its controlling the boost correctly.

Check, it, but after you thoroughly check for leaks in the couplers.

Never dig into a low boost problem until you've absolutely, postively, verfied there are no boost leaks.

Dave

Sounds like a boost leak.