We recently changed the clutch in the car to the Exedy Twin HD (old was slipping with new power). I've been driving around under boost as much as possible for the past couple weeks and haven't had any problems. Just within the past week I've started getting on it again. Well . . . Saturday I get on it and I hear a loud bang (sounded like a backfire). I let off the gas immediately and coasted to a light. Car idled fine, sounded fine, gave it a couple light taps on the gas pedal and it revs ok, seems normal. Come out on main road and give it a little more gas, but when it hits boost it doesn't really do much. Car drives normal, turbo spools, but only hits about 13-14 maybe 15 psi when it should be hitting around 26. Decided to take her home, checked pipes, lines, spark plugs, everyone's great.

Go ahead and do a boost leak test and find a couple couplings that have some seepage so fixed those issues and with 30 psi running through turbo it's perfectly quiet, no more hissing, just the standard air running through pipes. Just in case I missed something we took a bunch of soapy water substance and sprayed around on the pipes, couplings, clamps, vacuum lines, no foaming, no bubbles, nothing anywhere we could find.

Looking for some help in trying to determine problem. I've been driving car past couple of days and it drives fine, just missing a crap load of power.

Summary:
Loud Bang (sounded like a backfire) around 4k under full throttle and instantly let off and let car coast.
Boost max 15 psi Now (Before 26psi)
Car Starts, idles, drives fine pre boost
Post boost, turbo spools, no weird noises, spikes at 15psi sometimes 13-14

Did a boost leak test, checked plugs, checked pipes, couplings, lines, etc.

Thanks in advance for help

 

My first thought would definitely have been leak or popped off a line or something but if you already checked all that not exactly sure... Is your boost gauge reading any differently and idle and such as far as vacuum pressure?

 

Sounds like you have a boost leak now. The best thing to do is a pressure test.

Michael

 

Still sounds like a boost leak...

 

Vacuum at idle and rev is normal on the gauge, I would have thought a leak somewhere too, but we are pushing 30 psi through system and the only leaks we found were MBC (took line off and capped) and a couple couplings had some seepage but we fixed those and didn't make any change to boost under throttle.

 

what turbo you running? possibly wastegate needs adjusted?

 

Interestingly, the same thing had been happening to me WHILE my stock clutch was slipping. It happened several times just as you described around the same rpm and such. I had no boost leaks at the time either, had recently just gotten every single little last one situated.

Then one day I got that backfire again, and just after that backfire my motor blew. I hope for you this is not the same case.

 

Maybe bad plugs caused a misfire and put you into limp mode... just a thought since you already checked for boost leaks.

 

Running a cat?

 

First off thanks for describing the situation as clearly as you could. I hate the cryptic "loud bang...what is it?" threads.

It sounds like you're at wastegate boost (give or take) with the gauge maybe reading a lil high. Those aren't arbitrary psis. Did you throw any codes at all? Or just the noise?

It sounds to me like a hose popped off but you were very thorough checking all of that. When boost builds does it spool like normal but then just stop at the lower psi? Or does it build a little more slowly than you remember?

In my last Evo 8 at one point I was at wastegate boost and after days of trying to figure it out (including replacing the wastegate solenoid) we finally found my issue...it was electrical and the wastegate solenoid wiring somehow had gotten damaged slightly. But I was throwing wastegate actuator codes so we at least knew the general issue.

While I don't know what the bang was, your current situation sounds exactly the same as my wastegate being stuck open. Did you check the wategate solenoid hoses by chance? (under the stock airbox location) It may be a red herring but worth checking.

 

MetalSaber: Running Stock Evo 9 Turbo and WG

SvenDiesel: Well my clutch is not slipping, that's for sure. It's a brand new Exedy TwinHD with 660 miles on the clock. I just put that information in, since we did just put the clutch just under two weeks ago since maybe we forgot something or other people had similar experiences after doing this type of install.

Paperclip: I pulled the plugs and inspected each one. They are all in excellent condition.

SpoolinUp: BR TBE no cat

srcevo8: I've not seen any codes on the car except when we first started it up after the transmission and my buddy who put the intake back in forgot to plug in the maf. This was cleared before we even pulled it out of garage so all I've heard is the one bang that sounded like a backfire. We pulled the intake, filter, dv, checked turbo for shaft play, fins ok, dv looks ok, checked WG and hoses all look secure and wasn't able to find any leaks in them during the boost leak test. It seems to spool the same to me, but I've been driving a big *** turck around when we were doing clutch and been pretty easy on the car for past week and half during the clutch break-in so maybe it is spooling more slowly, but seems same to best of my knowledge.

 

Still having same problems =(

 

are you running a mbc? Did the hose pop off the wga oranything, etc? I can't remember what wastegate pressure is on the stock wastegate, lol.

 

Yes, running an MBC. Well, we disconnected the boost line for the leak test and reconnected it once finished. All lines at wastegate are on an double secured with zip tie and no leaks were coming from the hoses in that area and the mbc was reconnected by us and double secured with zip tie as well.

If it makes any difference and I am noticing some more popping in the exhaust than usual under
3k when decelerating in gear to light when 0% throttle. I don't recall hearing it like this before, but my memory isn't what it used to be lol.

 

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