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!

 

[krkline2gdsm]

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.

You said that the MAf is seeing its limis from boost creep. . Not even close. A stock 2G MAf can support up to 400hp. So I guess he is making 400whp+.

I suggested a swap of just the downpipe will not cause a boost leak already, idiot! But I was assuming he didnt have any issues before the fact.

I have heard of 16psi fuel cut but thats not what you suggested to begin with. Stock fuel system is good to about 15psi then after that, no way! Read what I sugested him to buy above in my first diagnosis and in my 2nd post, I agreed with a mod and said I assume that there was no previous boost leak issues.

 

[EclipticalGS]

I never said a Stock 2G MAF couldnt handle more than that, with a tune, I know stock 2g mafs can support 450hp, once again, with a tune.
The starter of this thread is running a STOCK tune...He was probably running so close to fuel cut with his stock downpipe, this new Downpipe ###### gave him juse enough creep to through the fuel cut on.

Also, Read my first post, at the bottom i tell him to get an AFPR for his 255, and get bigger injectors and a way to tune,

Because his stock TUNE cant handle more than 15psi.

 

[TurboDreamzGST]

Soo cap off the pcv valve or disconnect it before a boost leak test will stop air from entering the valve cover or no? Lol didn't mean to get everyone so heated all ### of my car

 

[EclipticalGS]

The maf does have a suitable limit for fuel cut when it calculates too much air and the STOCK TUNE says "fuel cut". Sorry if that was confusing, I was not saying the MAF had limits for HP or psi, I said the MAF has limits to tell the ECU what is exceptable, 16 psi on Stock Ecu tune is not exceptable without, tuning, fuel, injectors.
I wasnt even really talking to you, It's more like the RedEclipserBoy who has no idea what the situation of this thread is.

 

[TurboDreamzGST]

Anyone about that pcv? Just making sure my boost leak test is being done correcty

 

[EclipticalGS]

I usually leave mine in, but the only time i see postive oil pan pressure is when driving and my dipstick popped out once cause my cap was broken, just replace it to be safe, ther like 2.59

 

[TurboDreamzGST]

What cap are you talking about? The oil cap? I replaced the oil cap already...or are you talking about the cap around the oil dipstick? Thanks btw

 

[MrBoxx]

Warnings have been given.

Discuss this issue in a rational manner from now on, or all flame-filled posts will be deleted, even if they contain the recipe for the secret sauce. Period.

 

[jrohner]

No matter what's going on, 15psi is really close to fuel cut most of the time. Since fuel cut is based on airflow alone, it doesn't depend just on boost PSI. Even at a steady 15psi, airflow changes greatly with RPM. It also changes with temperature (on a cool morning, you'll probably hit fuel cut much easier than a warm afternoon). Also, one turbo could flow slightly better than another of the same model, or any other manufacturers variance to any part of your setup could make for differences in airflow. The point is, even two identical cars are not truly identical. So one person might be fine running 16psi, and you can only run 14psi. If the new downpipe even gained you 1 psi, which is hard to tell on a boost gauge, it may have sent you into fuel cut territory (or gained you airflow without a boost pressure increase). Airflow is what makes hp, boost psi doesn't actually mean anything, so just because you have to run slightly less boost, you could still have slightly MORE power than before.

You need to either get something to tune with to allow you to push fuel cut higher or remove it, or lower your boost slightly. Yes a boost leak test (BLT) is good to do, since any leaks could be adding just enough airflow to give you fuel cut, but even with no major leaks you may just be flowing too much air.

 

[No_Skillz]

Steps I would take if I were OP:

1. Warm up car and do BLT from turbo. Test 5psi above what you plan to run. Attempt to achieve 20psi that slowly leaks out over 30 seconds.
2. If heavy leaks from dipstick and valve cover, take hose off PCV and clamp it shut, re-do BLT and post results. If no more leak, PCV needs to be replaced.
3. While car is warm, do a compression test while WOT.

 

[EclipticalGS]

What cap are you talking about? The oil cap? I replaced the oil cap already...or are you talking about the cap around the oil dipstick? Thanks btw

I was talking about my dipstick cap, I actually bought a new oem dipstick and crimped the tube so mine didnt shoot out...

So much for my brand new PCV valve working, because I have 190 compression across the board.

But, I do not include my valve cover breather (port on middle left side of valve cover) because you never see pos. pressure there anyway, so I leave that capped on the intake tube.

BLT's are always good, I assumed from your first post you had already gone through that and somewhat elimed that from your list.

But i still agree 100% with Jrohner, your downpipe opened up some room for better flowing exhaust, which in turn created more turbo flow, which is too much for your stock tune.

 

[ramsack]

even brand new pcv valves seem to be boost/vac leaks. i just put a metal plug in the nipple for it in the manifold and kept the pcv valve on the valve cover to look emissions legal. if the pcv valve leaks boost from the manifold you will hear it through the breather and through the dipstick tube. it doesn't mean there is anything wrong with your motor like people are trying to say. if you heard sounds like that on a leakdown test, then yea you could say that then. i think you are hitting fuel cut too. fuel cut isn't about psi of boost, but psi of boost is directly related to amount of airflow. you could hit fuel cut at say 16 psi and it being 20 degrees outside and be fine running 20 psi in the 90 degree summer. it also doesn't matter what maf you run. fuel cut isn't a maf mechanism, it's in the ecu when it calculates duty cycles and load and whatnot from tps and maf readings. maybe he could be hitting fuel cut from more airflow from a downpipe plus a boost leak? arguing like this is crazy instead of actually helping him figure his problem out.

 

[pj91gsx]

my car wouldnt go past 5000k rpms, the ecu was bad. it ran really rich at idle, blowing black smoke somedays it wouldnt crank becuse no fuel or spark.

 

[TurboDreamzGST]

I'm picking up a new pcv valve today..they're cheap enough so it's worth it. I'll be trying to run the BLT tomorrow on a warmed up car and for the time being ill be leaving the boost at 13-14 to be on the safe side.

So if my pcv is allowing air into my valve cover during a boost leak test, what can I do to stop that from happening during the boost leak test?

 

[jrohner]

Check the PCV with an air compressor before you even put it on. If it doesn't hold, bring it right back to the store. I tested the one I put in my car (not a new one, just a random one I had laying around), and it held the 140psi of my air compressor with barely any seepage of air.

 

[TurboDreamzGST]

So all I gotta do is hook up an air compressor to the end of the pcv valve and pump air through it? That seems really simple thanks!

 

[ramsack]

yes it should block air in both directions. i wouldn't even run it tho. i would just get rid of the breather you have and run a hose to the intake.

 

[joegamma1]

yes it should block air in both directions. i wouldn't even run it tho. i would just get rid of the breather you have and run a hose to the intake.

WHAT? REALLY?
Both directions?
Then why'd they put it there? why not just a bolt to plug up that hole that is for POSITIVE CRANKCASE VENTILATION?
.

 

[jrohner]

A PCV valve is a one way valve. Common sense here guys come on. Why would it be a no-way valve?

 

[ramsack]

if it is a one way valve then it either leaks boost or it leaks vacuum. it doesn't leak either. it opens when there is weak vacuum and closes under any boost. with an air compressor blowing an extreme amount of air it should close both ways. watch your vac if you disconnect the hose from the pcv with the car running. IMO it's just there to meet emissions and the breather hose does way more.

 

[joegamma1]

I do know where you can get some "no-way valves", Home depot in the hardware isle next to the nuts. rofl....sorry i couldn't help myself.

Warming up the car up before the blt may make all the difference in the world, and the pcv may be a dead issue anyway. but if it is bad it will let air enter the valve cover from the intake(because being that it's a one way valve for positive crankcase ventilation, it lets air out not into the valve cover, because all engines pressurize the crankcase to some degree while running). good luck

 

[ramsack]

ya i'm just sayin if you use an air compressor to test it turn the pressure way down or use your breath. look at the angle on the plunger. too much air can lodge that in there if you blow from the head side with a compressor. either way it will act like a "no way" valve with too much pressure. the pcv system is supposed to draw fresh air in the breather part and pass the fumes through the pcv valve to be burned. i dunno i'd just rather block mine off and run the breather tube than buy a new one that will fail anyway hah. i've taken them apart and taken out the spring and hammered the plunger into the intake side to block them off and put it back together to block them off.

 

[joegamma1]

Is that a scale drawing? is the narrow end of the plunger a tapered solid piece or maybe just something that doesnt actually plug the hole when pushed all the way? Just a guide so that it stays inline to seat in the same position when closed? It doesnt seem like a pcv valve would limit the amount of ventilation. How does your car run with the pcv blocked off? Is it ok to do this?

 

[ramsack]

it is a drawing from the 1990 manual from mitsu. the plunger actually is tapered and it is solid so it does restrict the amount of air. if you take the hose that goes from the valve to the manifold off you will lose LOTS of vacuum and make the car stumble-idle. on my non-turbo i forced the plunger into the nipple side to block it off. it ran the same. on my turbo i used an appropriately sized drill bit and pressed it into the nipple on the manifold. ran the same. on my friends very modified car it kept running like it had a boost leak and we blocked the pcv off from the manifold and it made a HUGE POSITIVE difference in driveability and power. it's ok to do this and it will only hurt the environment supposedly. if you have a breather filter it will make it run better for sure because you're not puling in unmetered air.

 

[joegamma1]

Ok,

OP; keep us posted.