Dropping boost at high RPM
 

My car seem to struggle a little at high RPM. Boost pattern is normal until shortly after the changover and then it seems to drop off after about 6K to about 8-9 Lbs. I usually read about 11-12 w DP and Greddy PE exhaust and pull real hard up to redline. This started happening about a week after the Greddy was put on. Any ideas? Is this a sign of secondary turbo failing, or could this be related to the vacume/relay jungle. I have not done the vacume line upgrade yet.

Bump

greddy?
 

what is the greddy?

If you have or have not changed your air filters. Then do
so.. I recommend HKS or Apexi

your in japan:D in japan you have Trust, Greddy is the american name for Trust.

Check your vaccume hoses.

-j

Just fixed this problem, the 2nd turbo coming on makes more flow of air. This allows a crack some where between your turbos and your IC to open allowing a boost leak. I bought the Efini y-pipe b/c I found that the plastic crossover pipe had a slit that could hardly be seen when it was off the car. But under boost, it opens more. Some people have found that the rubber coupling connecting the ypipe and crossover has also been a problem. I would check that if I was you. Let me know.

My mechanic told me this was due to my boost spiking and the computer turning the boost down because it has just seen a spike of 12-13.

Radkns,

I have the same problem. My boost settles down around 8 psi after the spike to 12. I still have to check all of my vacum lines. Did your mechanic fix the problem? Or are you just supposed to live with less boost??

John

I having the same problem and so are many people on the board. I'm running stock boost so mine hits 10psi then quickly settles to 7. I'm thinking clogged cat or y-pipe but nothing noticable on the y-pipe.

This doesn't sound as much like a vacuum hose as it does a clog or crack in a pipe somewhere. Your typical vacuum hose problems have a route to that black plastic tank up top where boost accumulates for the 2nd turbo to spool up.

Definitely check your Y-Pipe. Check your cats for clogging and last but not least check your catback exhaust. For my previous FD, I bought an HKS Super Drager exhaust system when they first came out. That thing was a piece of shit and wasn't a true straight through design. I actually lost boost compared to the stock exhaust and was experiencing the exact problem you're having.

btw, i've heard they sell a different version of the HKS super drager exhaust that is a straight through 3" design.

Just for your information, and your cars well being, drop your mechanic! He obviously knows nothing about the way the FD works. The computer is stupid It has no clue as to what the boost actually is. You could be running 20 psi of boost and it still thinks you are only running 10 or so. That is why you have to upgrade your computer after just a few mods. This is also why you have to change pills, put manual boost control, or get an after market boost control system. Anyway sounds like your had better be careful with your mechanic. Oh, I would guess a crack somewhere as well.

It might not be anything at all. The stock boost pattern is 10-8-10 then it drops lower as you approach redline. It might be boosting correctly but it just seems like it's losing power because you get the abnormal spike.

Does the boost cut suddenly after 6000rpm? or is it gradual?

My mech told me that I need a new ECU, and I dont think he is an idiot, they are VERY experienced in FD's and all they do is RX7's. Are you sure the ECU doesnt monitor boost. I thought thats how the fuel cut worked. Anyways Pressurized, I think your right. Alot of it may be my imaginaton with the spike. It settles down slow to about 8 or so. One thing I have noticed (I think)is that if I accelerate slowly up to where the 2nd tubo kicks in and then hammer it the boost stays at 10lbs thus eliminating the spike at changeover.

Yea, I am absolutly sure it does not monitor boost. I just knows when there is boost. The computer just thinks evrything is stock it runs on a map system. It knows throttle position, engine rpm, and if it has boost (not how much). Well it also knows a few other things, but the main thing is that it has no idea how much air is actually going to the engine. It has mapped rates of fuel and timing for different situations of throttle position rpm and boost. This is why you have to be careful how much you mod with the stock computer. It is only mapped for stock and the more you mod the leaner it gets. The computer has no way of adjusting boost. It relives air from the waste gate at a mapped rate that when stock produced the right amount of boost. when you mod you increase the amount of air that is moved and the solinoids don't vent the right amount of air causing the extra boost. The computer still thinks every thing is the same, therefore oly releasing the same amount of fuel with the increased volume of air creating a more lean condition. Too lean and boom!