Car hits brick wall after downpipe installation...WTF??

[TurboDreamzGST]

Ok so I'm having a problem with my 98 GS-T. I just recently had my 3" straight pipe downpipe installed. Now i got on the car on the highway and its boosting just fine and hitting and holding 15 psi no problem but once the RPMS hit around 5,000 the car lets out a HUGE backfire and feels like its hitting a brick wall almost like its hitting fuel cut or something. Now i checked all the hoses around the turbo and wastegate, vacuum lines and intercooler lines and found nothing after running a boost leak test. This problem only started happening once the downpipe was installed. Here's the funny part: my exhaust is setup like this...OEM manifold on big evo3 16g, megan racing o2 housing, 3" cat-less downpipe, a 6 inch piece of stock sized piping where the O2 bolts in (because the guy at the exhaust shop was too lazy to do the job correctly and re-tap a hole for the O2 sensor in a new 3" piece of piping, i will be having this fixed asap and i thought maybe this could cause a problem like i'm having but im not sure ) and than that piece is welded up to a 3" piping running to the back of the car. What could it be?? i dont think its fuel cut because before the downpipe was on i was boosting the exact same and it would redline with no problem. Any ideas?? i'm stumped!

 

[EclipticalGS]

Fuel cut is what I vote for. Yes, you can turn up boost to 17psi sometimes 18psi with a stock t-25...but when you add a B16G with more flow, you can get fuel cut at 15psi sometimes lower.

He said he was holding boost, so it wasnt leaking, just as long as your car isnt running really rich or surging, i wouldn't say it's a boost leak. You said turning the boost down to 12psi fixed it? Yes, that was your problem.

Adding a 255lph fuel pump needs an AFPR, that pump will overrun the stock. New injectors need to be tuned no matter what. The tuning software you use will be what gets you past fuel cut.

 

[doctor_shock10]

just turn down the boost or get bigger fuel pump and injectors and tune.

 

[TurboDreamzGST]

Yea I was boosting perfectly fine and hitting 16 psi consistently and it would hold all the way to redline if I let it before the downpipe was installed and after getting the downpipe installed that's when I ran into problems at 16 psi. No sputtering or any symptoms of a boost leak but it's always a good idea to check so I will anyway. 13-14 psi seems to be holding fine until redline now without a problem at all. Thanks to everyone for all the input. The more info I have the better!

 

[MrBoxx]

You can hold any psi steadily and still have a boost leak.

 

[krkline2gdsm]

You can hold any psi steadily and still have a boost leak.

If you didnt touch anything else but the downpipe and started having this problem, its probably going to be boost creep/fuel cut.

Turn down the boost until you get bigger injectors, a fuel pump, and something to control it with

 

[TurboDreamzGST]

Yea nothing was touched except for the downpipe. 16 psi before the downpipe was fine, 16 psi after the downpipe and problems occurred. It definitely felt like I was hitting fuel cut when the problem happened so I'm pretty sure it was fuel cut. I'll still run the boost leak test but after reading everything I'm pretty sure fuel cut was the culprit. Thanks again for all the info. I understand I can hold boost and still have a boost leak but if I was holding 16 fine before the down pipe but now can't after the down pipe I'm leaning towards fuel cut especially since that's exactly what it felt like.

 

[MrBoxx]

Once again, in case you didn't understand: Your boost leak is CAUSING the fuel cut. You were leaking before, but the turbo was being restrained by your stock downpipe, and thus wasn't moving enough air to trigger fuel cut. Remove the restriction, and now your turbo is free to spin up and move LOTS of air, which is all leaking out, keeping your system at 16psi just like before, and when the MAS sees you moving that much air, you get fuel cut.

Installing a new pump and injectors isn't going to solve your fuel cut problem if it's a boost leak.

 

[krkline2gdsm]

Once again, in case you didn't understand: Your boost leak is CAUSING the fuel cut. You were leaking before, but the turbo was being restrained by your stock downpipe, and thus wasn't moving enough air to trigger fuel cut. Remove the restriction, and now your turbo is free to spin up and move LOTS of air, which is all leaking out, keeping your system at 16psi just like before, and when the MAS sees you moving that much air, you get fuel cut.

Installing a new pump and injectors isn't going to solve your fuel cut problem if it's a boost leak.

100% correct. I assumed he atleast did a boost leak test before anything else. When fuel cut happens, boost leak test should be the 1st thing you do.

 

[TurboDreamzGST]

Yea that's why I said I was going to do another boost leak test. I did one immidiately after the problem started happening but did it on a cold engine and had air leaking from my dip stick and valve cover breather at around 15-16 psi but that was the only places it was leaking from so I will be running another test on a warm engine and hoping to run 20 psi through the system and see what results I find. I'm not saying that it isn't a boost leak all I am saying is that I turned the boost down to 13-14 psi and it is running fine for the time being since it is my daily driver and I have school 3 days a week and work 4 days a week so I need the car to be drive able. The boost leak test will be run as soon as possible.

 

[krkline2gdsm]

had air leaking from my dip stick and valve cover breather at around 15-16 psi but that was the only places it was leaking from

You have other issues. I would consider doing a compression test first and if you have the tools, do a leak down test. You might have BIGGER problems.

 

[TurboDreamzGST]

I ran a compression test (again on a cold motor) and came up with 155-160 across all cylinders.

 

[EclipticalGS]

What are you guys talking about? How is a boost leak going to cause this kids fuel cut....

Maybe if he had fuel cut at like 13-14psi id see it being a boost leak, because your seeing 13-14 manifold pressure, but the maf is seeing more because your losing some through a leak.

But he is lucky hes getting fuel cut at 16psi. Ive seen fuel cut at 14psi with a B16g Because our stock blowthrough sees too much airflow. There was no boost leaks on this ^^^^ car.

Also my car hit fuel cut @ 16psi when my first small 16G went on before I got this Big16g

 

[Red97Eclipseboy]

What are you guys talking about? How is a boost leak going to cause this kids fuel cut....

Maybe if he had fuel cut at like 13-14psi id see it being a boost leak, because your seeing 13-14 manifold pressure, but the maf is seeing more because your losing some through a leak.

But he is lucky hes getting fuel cut at 16psi. Ive seen fuel cut at 14psi with a B16g Because our stock blowthrough sees too much airflow. There was no boost leaks on this ^^^^ car.

Also my car hit fuel cut @ 16psi when my first small 16G went on before I got this Big16g

Have you read anything in here from mods or wisemen? You really can't be for real. Boost leaks are a MASSIVE reason for fuel-cut. I can't believe after reading this thread you don't udnerstand that fact. FACT. And how do you know the car that had "no boost leaks" was hitting fuel-cut? It could have been something else.

Using your logic, no DSM should ever blow a motor due to a lean-condition because we'll just get fuel-cut at a certain PSI. You're wrong. 100% wrong. Without software to tune with, at WOT, his car is going to shoot for the factory 9.5:1/9.7:1 AFR. That in itself can max-out injectors as well. That will cause a sputter because the injectors will get stuck if they're IDC maxed-out.

You're pretty confused about fuel-cut. Read up on it. Again, a boost level DOES NOT dictate fuel-cut.

 

[ramsack]

seems like your pcv valve is leaking

 

[EclipticalGS]

Have you read anything in here from mods or wisemen? You really can't be for real. Boost leaks are a MASSIVE reason for fuel-cut. I can't believe after reading this thread you don't udnerstand that fact. FACT. And how do you know the car that had "no boost leaks" was hitting fuel-cut? It could have been something else.

Using your logic, no DSM should ever blow a motor due to a lean-condition because we'll just get fuel-cut at a certain PSI. You're wrong. 100% wrong. Without software to tune with, at WOT, his car is going to shoot for the factory 9.5:1/9.7:1 AFR. That in itself can max-out injectors as well. That will cause a sputter because the injectors will get stuck if they're IDC maxed-out.

You're pretty confused about fuel-cut. Read up on it. Again, a boost level DOES NOT dictate fuel-cut.

Fuel cut still happens when our 2G maf sees too much airflow, He said that he put a completely unrestrictive downpipe on which can boost creep, that boost creep could have taken him over the MAFs suitable limit for fuel to cut.

He said his car acts fine at 13-14...So I dont understand what your saying?

He also just noted he did a BLT and his dipstick and valve cover breather leaked only..

Hmm, sounds like a giant boost leak. not

 

[TurboDreamzGST]

My pcv is leaking? Could you explain more please? I'm going to be running another boost leak test on Sunday on a warmed up engine and see what I get. I'm still sticking with the problem being a boost leak. The moderators and wisemen and such make a good point and I trust their judgement. Plus a boost leak test takes 20 minutes so it's def worth running even if I wasn't experiencing problems.

 

[Red97Eclipseboy]

Fuel cut still happens when our 2G maf sees too much airflow, He said that he put a completely unrestrictive downpipe on which can boost creep, that boost creep could have taken him over the MAFs suitable limit for fuel to cut.

He said his car acts fine at 13-14...So I dont understand what your saying?

He also just noted he did a BLT and his dipstick and valve cover breather leaked only..

Hmm, sounds like a giant boost leak. not

A downpipe does not overrun our MAFs, sir. Do understand airflow and hertz? Look at my profile. With all those mods and 23psi on pump, I still have my stock 2g MAF. Where's my fuel-cut? And I'm still at the factory 43.5psi of base fuel-pressure. If you read him more carefully, he wasn't holding boost with his test. And I don't need to hear from you what causes fuel-cut on our cars.

And if you don't think his dipstick blowing out and air leaking out of his crank-case port isn't a leak or a big deal, then you really need to stop in this thread. I can't fix your stupid.

 

[EclipticalGS]

K, when you dont find a boost leak, youll realise it's jsut boost creep and your hitting fuel cut like every other person in here thats ever tried cranking the boost on their 16g.

I know what the dipstick pressures from, usually bad pcv valve.

But, thats not a bad boost leak, I get positive crank pressure from a brand new pcv, dsms are known for popping dipsticks in boost..

And, Red 97 Eclispse, you have a ####ing tuning system....He doesnt!!! You will always eventually hit fuel cut without tuning software

 

[krkline2gdsm]

Fuel cut still happens when our 2G maf sees too much airflow, He said that he put a completely unrestrictive downpipe on which can boost creep, that boost creep could have taken him over the MAFs suitable limit for fuel to cut.

So when you upgrade to a 3" downpipe, you should convert over to an EVO MAF, GM MAF, or run SD?

Killing me...

 

[EclipticalGS]

Apparently you havent been following this post. He ran 15psi stock downpipe, no fuel cut. He put on a un-restrictive down pipe that causes creep in many cases. Now he has fuel cut.

From an install of just a downpipe, how can he acquire a boost leak between then? Idiots

I cant believe no one heres ever heard when you try cranking the boost on a stock car with no tuning software, it almost always fuel cuts right at 16psi.

 

[BIRDCLAWTSi]

i found a small boost leak at the signal line to my boost gauge inside the car, but i didnt find it when i did the boost leak test. i found it when i installed my wideband. i couldnt hear it and i didnt know it was there. it did however change my idle correction when i fixed it.

 

[TurboDreamzGST]

Well I replaced the pcv valve about 4 months ago so idk if a bad pcv is even in question but since they are so cheap I can pick one up tomorrow. Now aside from taking off my intake, disconnecting my MBC and running the hose from my wastegate right to my turbo, there is no other steps I need to do before running the boost leak test right? Just wanna make sure that the reason there is air coming from the dipstick or valve cover breather is not because of something i am doing incorrectly.

I went from a 3" cat back system with a Megan racing 02 housing and than threw on the cat-less 3" down pipe making it a full 3" turbo back exhaust.

 

[EclipticalGS]

air out of your dipstick is pcv and valve breather, its not good to shove air into your valve cover...

I have a brand new motor, brand new pcv, and still managed to shoot my cobbled and loose dipstick out.

 

[joegamma1]

Air from the breather is metered and put back in the intake, post maf. Another blt with the motor warm will help. it may be possible that the turbo is now creeping because of the open exhaust and your boost leak doesnt "show up" until you get above 16psi. which would be why you could only get to 15-16psi before, even on a cold motor. just my .02

 

[TurboDreamzGST]

Do I have to remove my pcv valve or cap it off or anything before running the boost leak test? I didn't think I had to but now I'm starting to second guess myself. How could air be getting into the valve cover if my compression test numbers are coming back good?