This developed recently, I was getting 10-8-10 (sometimes 10-8-11_ with the boost dropping down to 9 as I hit redline. Within the last week or so I'm seeing the primary boosts to 10psi, 8 at the transition, immediately back to 10/11, but by 5.5k rpm the boost drops down to 7 where it sticks until redline. I figured it was my main cat (original had 103k miles on it, in need of a replacement due to age/mileage anyways, and when I took it off, lots of cat innards fell outta the downpipe side), but I got a newer one on it now, and I'm still seeing the same boost pattern. I'll check the charge relief valve and wastegate actuator tomorrow. Anybody experience this before?

Thanks!

 

That doesn't seem like an abnormal boost pattern, as the boost does fall a bit as it reaches redline.

 

There is now some sort of restriction in the air flowing path - check intake and exhaust.

 

i agree although you might possibly have some kinda restriction or a vaccum line not quite on.

 

Well I removed all the intake pipes, checked the vacuum lines going into the charge relief valve and wastegate actuator, tightened all the large hose pipe clamps going from the turbos to the IC to the intake elbow. The only "loose" vacuum line was going into the vacuum chamber, which I zip tied. With that done I'm getting 10-8-11-8 (with the psi dropping to 8 around 5.5k rpm and holding there until redline). I wouldn't be concerned if the drop was at around 6.5k rpm (which is what would happen on my first FD), but the drop so close to transition makes me think that something is amiss.

Could it possibly be my catback? I know the stock ones were pretty restrictive. I bought a used stock catback in 2001 (I'm in the quiet exhaust camp) and it probably had about 30k miles on it when I bought it and I've put nearly 30k miles on it since. Could it be that the catback has gotten more restrictive with age?

 

I've been after that problem ever since i got my fd. Never really quite fixed it. It comes and goes with my car. and I have full open exhaust, intake, ecu, IC etc. After I replaced my twins, it did help, but i still loose a pound. So I don't know what to tell you really.

Amel

 

Did you test your check valves while you had the UIM apart:

PCV
Purge Control
Double Throttle Control
Turbo Control
Pressure tank

Boost would steadily drop towards redline in my car when I first got it. I did a hose job and the check valves. Every check valve was bad.

Sonny

 

OK, a little more info... You figure after owning these things for over 6 years I'd know how to do a boost test. I was testing the car in 1st and 2nd gear (duh), until I remembered today that you can only do a boost test in 3rd or higher. Here's the deal, in 1st and 2nd gear, I'm getting 10-8-10-7/8, with the boost dropping to 7 or 8psi at around 5.5k rpm. That's normal (from my general understanding of FDs). In 3rd, I'm getting 10-8-10-7/8-8/9, with the boost dropping to around 7-8psi at around 5.5k rpm, and then actually climbing back to 8-9 rpm as you head towards the rev limiter... Going uphill I actually saw 10-8-11-7-10 , where the boost dropped to 7psi at 5.5k rpm and climb back up to 10psi as I approached redline. As it is the car doesn't feel any slower than before (just a millisecond flat spot at 5.5k rpm), so I think I won't mess with it until I do the vacuum hose job (if I still own the car, it's forsale), later this summer.

Thanks!

 

when that happened to me it was my cat that was starting to clog.

mine holds 10 psi all the way to redline in every gear. but i haven't checked 5th yet, but...