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!

 

[ziggo0]

Boost Creep?

 

[juanpac0]

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

 

[dakota_gsx]

yes its fuel cut. i had the same thing happen to me. i turned up the fuel pressure just a tad and it solved the problem. just dont turn it up too high like the dumbass mechanic did to my car because then your afpr will blow, your engine/intake/turbo/intercooler/cylinders will all fill up with about 15L of fuel and youll be in for a nasty drainage session with your dsm. and its not a fun sight seeing stupid amounts of fuel shoot out of your spark plugs. not fun at all.

 

[No_Skillz]

Careful with the misinformation, friends. Changing anything to your fuel setup will not cure your fuel cut. Fuel cut is almost always a result of your ECU detecting too much airflow at the intake. Your ECU does not know or care about changes to your fuel settings. Since a downpipe is the newest mod, it can be assumed that the less restrictive exhaust is allowing your turbo to boost more. Basically you've got too much boost going on. Either it's creeping and you're not noticing, or it's leaking out and you need to do a more comprehensive boost leak test.

 

[BoostFrenzy]

yes its fuel cut. i had the same thing happen to me. i turned up the fuel pressure just a tad and it solved the problem. just dont turn it up too high like the dumbass mechanic did to my car because then your afpr will blow, your engine/intake/turbo/intercooler/cylinders will all fill up with about 15L of fuel and youll be in for a nasty drainage session with your dsm. and its not a fun sight seeing stupid amounts of fuel shoot out of your spark plugs. not fun at all.

Hyperbole: Check...
Wrong Information: Double check

 

[TurboDreamzGST]

Ok I ran the car hard again, this time with my friend in the car. He was watching the boost gauge the whole time while I floored it n tried to get it past 5000 rpms but again it did the same thing and he watching the boost gauge hit 16psi n hold there. Could it still be boost creep or fuel cut and if so what should I do? Just turn the boost down to say 14 or 15?

 

[No_Skillz]

Ok I ran the car hard again, this time with my friend in the car. He was watching the boost gauge the whole time while I floored it n tried to get it past 5000 rpms but again it did the same thing and he watching the boost gauge hit 16psi n hold there. Could it still be boost creep or fuel cut and if so what should I do? Just turn the boost down to say 14 or 15?

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.

 

[Smallfry311]

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

+1 on this

 

[TurboDreamzGST]

Well I turned the boost down to 12 to see ### would happen and the problem went away so u guys were all right! Thanks! But isn't 16 psi safe to be running without me hitting fuel cut?

 

[Sp1kE]

Obviously not.
Your profile says nothign about a fuelpump or even a rewire.
16psi out of an evo3 it obviously overdoing it.

 

[No_Skillz]

Well I turned the boost down to 12 to see ### would happen and the problem went away so u guys were all right! Thanks! But isn't 16 psi safe to be running without me hitting fuel cut?

It is safe, but if you have a boost leak then the ECU is going to think that you are running more boost than you actually are. I.E. if you are running 16psi but 4psi is leaking out, then your boost gauge still shows 16psi but the MAF detects 20psi at the intake. ECU reads from the MAF, doesn't know or care what your boost gauge says.

 

[TurboDreamzGST]

Yea I have a 255 pump and aeromotive AFPR I haven't installed yet because I'm waiting for some 650 injectors first. Well at least the problem is fixed. Thanks guys! I'll keep it around 14 psi until I throw my fuel mods in. I just thought 16 psi was safe to run with my mods this far.

Yea I ran a boost leak test up to 16 psi and didn't find anything but I do have an SSA FMIC kit so all the rubber intercooler pipes are gone so I don't think the leak would be from the aluminum piping but I'll run another test and see if I find anything. Thanks for all the input! I never thought about that.

 

[No_Skillz]

Yea I have a 255 pump and aeromotive AFPR I haven't installed yet because I'm waiting for some 650 injectors first. Well at least the problem is fixed. Thanks guys! I'll keep it around 14 psi until I throw my fuel mods in. I just thought 16 psi was safe to run with my mods this far.

Yea I ran a boost leak test up to 16 psi and didn't find anything but I do have an SSA FMIC kit so all the rubber intercooler pipes are gone so I don't think the leak would be from the aluminum piping but I'll run another test and see if I find anything. Thanks for all the input! I never thought about that.

Fuel mods aren't really going to do you any good like stated in my earlier post. Fuel cut is determined by the ECU.

You should do a boost leak test up to 20psi. The intake system from the turbo should hold 20psi and slowly leak down over ~30 seconds or more.

 

[TurboDreamzGST]

yea i never even thought of a leak causing the problem like that. I'll def be running another boost leak test as soon as i can. I just always assumed if i had a boost leak i'd get the normal symptoms such as sputtering and bucking and blowing black smoke, no matter how small the leak is. But you just shed some new light on this problem that i didnt know! thanks for the help!

the other problem i noticed is that when i'm doing a boost leak test, it won't hold pressure. It slowly leaks out but only leaks from the oil dip stick and the valve cover breather. Is there any way to get an accurate result for the boost leak test without having to replace the valve stem seals just yet? (i believe leaking valve stem seals cause this problem, but yet i dont lose or burn any oil so im a little confused)

 

[tkelly27]

Valve stem seals keep oil off the valve stem, they don't do anything for holding pressure. You have pressure leaking past the piston rings in the cylinder with an open intake valve. This has been normal for me, and I'm sure for everyone else because I had 95% on my leakdown test. It will be less if you do the BLT on a warmed up engine.

Hit all your couplers and gasket areas with soapy water from a squirt bottle. A leak will bubble up.

When you get 650's you'll have to get something to compensate for them, this should get rid of your fuel cut, be it a chip, afc, or link.

No Skillz has given you the best information so far. I'm not sure if he mentioned this, but you could easily be moving too much air at 16psi without a boost leak, especially with a bigger turbo. When you went with a 3" pipe you decreased the backpressure the turbine has to work against, which decreases the backpressure in the manifold, which will give you a higher massflow.

If you don't have a logger, or boost leaks, you have to assume you've hit fuel cut even though you didn't at 16psi with the smaller exhaust.

*edit* i see you already have an AFC. Without compensation for bigger injectors you are still feeding roughly the same signal to the ecu. You could potentially increase the fuel pressure and compensate for it with the AFC, but if you're not logging and don't have a wideband you'll just be shooting in the dark.

 

[TurboDreamzGST]

That's great info! I tried the BLT while the motor was cold so I'll def be trying it after it's reached it's normal operating temp. I didn't even think about the piston rings because when I did a compression test the numbers came back 55-60 consistently across all cylinders which I didn't think was too bad. I'd like to perform a leak down test as well but I'm not sure how. I searched on here and found some instructions on how to do so but they weren't very clear and a bit confusing. Any write ups you can suggest that you found well written and clear?

I meant 155-160 on the compression test results sorry

 

[907gs-t]

Damn that compression test seem's low considering mine came out to be 185,180,182,180 & thats with 135,000 miles on my 98 GS-T.

 

[TurboDreamzGST]

Oh wow really? That was the results on a cold motor....should the motor be warmed up before I do the test?

 

[cordova]

its a fuel cut wuth that turbo it is recommended to change fuel pump to walbro 255 i had to do it when i upgraded the turbo to the evo 3 if u dont want to ## gonna have to bring ## boost down to like 12psi and it wont do it anymore

 

[TurboDreamzGST]

Well I got the boost at 13-14 now with no problems now so I'll leave it there. Should I run a compression test once the engine hits normal operating temp or cold? And is it ok to run a 255 rewired with stock injectors and fuel pressure regulator and have no bad side effects or should I wait and install the 255, 650 injectors and AFPR all at the same time?

 

[Eeeeky]

Definetely fuel cut. Probably just a lack of fuel under bigger that stock boost. gotta get that fuel level up.

 

[TurboDreamzGST]

That's what I plan on doing next but can I throw the 255 pump on with stock injectors and stock fuel pressure regulator with no bad side effects? Or do I have to wait and install the pump, injectors and FPR at the same time?

 

[MrBoxx]

Anyone who says that fuel cut can be solved by installing a 255lph pump needs to stop posting here.

OP, you have a BOOST LEAK. Do your test, find your leak(s) and fix them. Use soapy water on your intercooler pipes, intercooler, intake manifold gaskets, throttle body gaskets, shaft seals, BOV, brake booster, BOV, and FPR hoses, everything.

Get a logger and find out what your airflow numbers are, as well as your injector duty cycles. These are going to help you see if you're hitting close to 100% IDC when you boost up to 16psi. Assuming you fix your leaks and you're still hitting high IDC's then it's time to go to a bigger injector and fuel pump. If you already have the 255lph, then YES, you need to install the AFPR at the same time. Otherwise, you risk overrunning the stock FPR return orifice.

 

[TurboDreamzGST]

^^^ Exactly the kind of answer I was looking for. Very clear, to the point and descriptive! Thank you so much!