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!

 

[TurboDreamzGST]

Well i picked up a new pcv valve anyway since it cant hurt (and plus it only cost 5 bucks anyway). I'll be running a boost leak test as soon as possible and i'll make sure the car is taken for a nice ride before i run the test to make sure its warmed up properly.

 

[jrohner]

The point is to suck gas fumes out of the crankcase, so not to contaminate your oil. If it closed with boost, and with vacuum, it wouldn't do anything ever. Vacuum is sucking through it, not blowing through it backwards anyways, there's a difference..

 

[TurboDreamzGST]

I think i'll also be taken the breather filter off of the side of my valve cover and replacing with a hose back to the intake like it came from the factory with. The only reason i took the hose off, plugged the hole on the intake, and put a breather filter there was to keep oil out of the intake.

 

[jrohner]

Just run the breather line to a container of some kind, even a quart oil jug works. As long as it's vented some way, so the crankcase pressure has somewhere to go when you're boosting.

 

[ramsack]

if you take the hose off the pcv valve it will kill your vacuum. you will also hear it open and close. it closes shut from idle vacuum. it opens when you're cruising around. the less vac you run, it will open more, and once it hits boost it closes on the other end. read the red highlight. it WILL close under idle vacuum. it doesn't say it but it does in my experiences. also it says about normal driving conditions. more boost exempts from that and the pcv valve ###### won't hold up as long. i would just get rid of it. if you run a hose to the intake instead of a breather it will get rid of any fumes a pcv valve will, you just won't have fresh air mixed in with it.

 

[jrohner]

The hose to the intake pipe doesn't suck anything, it's just a vent. To suck it would have to be angled, not perpendicular. Without the PCV system, your oil is not as clean, and water accumulates because it doesn't get sucked out. When I wasn't running a PCV valve, my catch can was full of water in a couple drives in the winter.

 

[ramsack]

so the air filter and maf have ZERO restriction to them? they DO have vacuum albeit slight, it will suck fumes out of the crankcase. it doesn't have to have a angled tube to create vacuum. i don't have a pcv valve on my car and i don't have any abnormal amount of water in my crankcase. if there was then my oil cap would have that famous whitish foam on it. and actually if you blow across a straw in a cup perpendicularly it will bring water up and atomize it. try it

 

[JayRolla]

I was tired of buying Pcv valves so I blocked mine off at the manifold and vent the Pcv to my catch can. Been running it like that for over 6 years.

 

[BIRDCLAWTSi]

i have mine blocked off as well, i have both ,the valve cover breather and pcv with hoses running off to the side near the tranny mount until i make a catch can, pcv and breather are metered orifice's and are compensated for.

 

[jrohner]

What does any of this have to do with the thread anyways?

 

[Clinical]

Op I'm not sure if you're still having the same issue cutting out or not and I'm not sure if its been mentioned yet.

I was having the same issue minus the backfire and it was simply a plug on the coilpack sitting loose and in full boost the car wasnt getting spark however it was driving normal when not all the way in the throttle.

Just incase its something simple..

 

[casperfast]

i had a similar problem, was boosting and holding fine and i couldnt find a boost leak.... turns out the leak was a hole so big i could but 2 fingers in it, and thats what made it hard to find. it was in the middle of an old rubber hose. i couldnt find it cause i couldnt see it. i found it when a drop from my spray fell down then slammed against the block.... yureka!!! new hose... no problem

 

[jrohner]

Once you've experienced fuel cut, I can't see you mistaking anything else for it again. It's hard for us on here to say for sure, but from your first post it does sound like fuel cut to me.

New NGK spark plugs (I like BR7ES) gapped at .026 would be a good thing to do if you're unsure. Check over your plug wires really good too, and make sure they fit the plugs and coils tight.

A couple years ago, I had to replace the plugs and coils, and do some 'adjustments' to my plug wires to get it running right again. When I would get full boost, it would cut out and not come back for a couple seconds. It actually filled my oil with E85 one time when it cut out. It felt a little bit like fuel cut, but not nearly as violent and it would miss when it came back. A couple times I even had to turn the key off and back on to get it to quit missing afterwards.

 

[TurboDreamzGSX]

Sounds like fuel cut to me. I would still check for a boost leak as mentioned about because it wont hurt but def. sounds like after the install of the downpipe, it allowed more flow for the turbo causing you to boost more and hit fuel cut.

 

[forumboarder154]

Your 3" downpipe is causing you to boost creep, and due to your stock injectors you run out of fuel and hit fuel cut.

+2 We've all been there

Time to get bigger injectors, fuel pump, tuning mechanism and tune for more of them horses.

 

[ramsack]

fuel cut is in the ecu. it won't be fixed by just getting bigger injectors and whatnot, you need to delete the fuel cut function out of the ecu.

 

[16vdohcturboawd]

You've probably got a massive boost leak somewhere. You said you did a boost leak test. What were the results? You can turn the boost down for now, it will help depending on how bad your leak is.

+1 on this, once I put my 2.5" turbo back on my car did the same exact thing. Turns out my stock sidemount at the time had a huge hole corroded in the upper pipe about the size of the 1/2 dollar.