car barely accelerates, wont boost past 10psi, and BOV sounds like a paintball gun

[Novablue454]

The Car:
1990 Talon TSi AWD.

Mods:
Walbro 255lph, Apexi SAFC, Apexi N1 catback, TurboXS type H-RFL BOV, unknown MBC (18-20psi), and an Autometer boost guage.

The Problem:
My car has been running just fine for a while now, so this came out of nowhere. tonight a friend and i were driving around, and i got in it from a stop sign. it went fine to 3rd gear and then i let off. all seemed well untill a few seconds later the exhaust started making popping sounds. now when i try to accelerate it wont get past about 10psi and then the BOV makes a popping sound like a paintball gun or one of those old nerf ball launchers. (sorry thats the best description i can give).

So heres what im thinking:
I might have fouled the plug (im running a walbro 255 with no FPR untill tomorrow when i can buy fittings and stainless line tomorrow). My thought is that this would cause it misfire, temporarily stopping (or reducing) exhaust gas flow to the turbo, causing the BOV to think that I let off the gas and vent. The BOV venting and then shutting could cause the low boost/low acceleration that im seeing. The guage reads ten psi, but when it starts popping is jerks back and forth from 8-10.

Any other suggestions?

 

[20MIRAGEGT]

check for exhaust leaks .

 

[JayRolla]

Did you check the plugs, I bet that is the problem. Also is the bov recirculating or not, if not than thats a huge problem there.

 

[Novablue454]

no, the BOV is not recirculating, but its been running ok for weeks like that. (i know its not going to run great).

im going to go check the plugs now.

 

[PSI NRG]

My thought is that this would cause it misfire, temporarily stopping (or reducing) exhaust gas flow to the turbo, causing the BOV to think that I let off the gas and vent. The BOV venting and then shutting could cause the low boost/low acceleration that im seeing. The guage reads ten psi, but when it starts popping is jerks back and forth from 8-10.

Any other suggestions?

That is not possible. A misfire is just a tempory glitch in ignition timing where the plug fires a split second after or before its suposed to or doesnt fire at all This would not cause exhaust flow to stop or reduce any at all because it only happens for a second and usually on 1 cyclender. Even if it kept occuring you couldnt stop exhaust flow let alone reduce it enough to notice. Further more the amount of exhaust flow through the turbo has nothing to do with the blow off valve. Its all about the throttle body. When the throttle body is open the bov is pulled shut by the velocity of the air rushing past it into the engine. When you let off the gas the throttle body plate closes not allowing air into the motor and that air pushes the BOV open because of the pressure that builds up in the piping.

My guess is you have a boost leak somewhere which when the turbo starts to build boost some of the registured air is excaping out causing the all ready calibrated air/fuel mixture to be off making it run rough or backfire and jerk. Also venting the BOV will cause this. Do a boost leak test and recirculate your BOV if you havent already.

 

[oldman]

1. You need to replace that BOV with something that can be recirculated.

2. You already know about the AFPR.

3. Check for leaks.

4. Are you tapping your BOV line for the MBC?

You need to stop abusing your car damn it.

 

[Novablue454]

all the plugs look good. i dont have a spark tester so i can actually test that, but they are all medium-gray in color. they are champions though, so when i go to work tomorrow im going to pick up some NGKs.

im thinking of trying to diagnose weather its an engine issue or turbo system issue by disconnecting the upper IC pipe at the intake manifold, and taking it for a jog around the block. theoretically, this should take boost out of the equation. Would the car run ok and just like an NA with this done, or would it have issues? becasue if it ran fine with no boost, its a turbo system issue, and if it still does it, its an engine issue, correct?

please, any input is appreciated.

 

[Novablue454]

I had a homemade MBC on it which wasnt tapped into the BOV line, but i just got my car back from a shop, and they called my mom and convinced her that wasnt reliable and so they decided to replace it with a real one. And when i just checked, sure enough, it was tapped into about 4 inches from the vacumn port on top of the BOV.

What does this mean?

 

[93_tsi_fwd]

check your intercooler piping or your intercooler. something there is causing a boost leak.

samething happend to my car.

 

[PSI NRG]

all the plugs look good. i dont have a spark tester so i can actually test that, but they are all medium-gray in color. they are champions though, so when i go to work tomorrow im going to pick up some NGKs.

im thinking of trying to diagnose weather its an engine issue or turbo system issue by disconnecting the upper IC pipe at the intake manifold, and taking it for a jog around the block. theoretically, this should take boost out of the equation. Would the car run ok and just like an NA with this done, or would it have issues? becasue if it ran fine with no boost, its a turbo system issue, and if it still does it, its an engine issue, correct?

please, any input is appreciated.

WTF You do realize that if you disconnect your intercooler piping your car probably wont run at all. How would that determine if its a engine or turbo related issue?

Please just dont start to do things to your car and assume that waht you are doing will help you figure out a problem. Obviously you have very little experiacne with these cars
Do a boost leak test first before you start pullin intercooler pipes hoping it will determine if something is right.

 

[Novablue454]

your right, i do have little experience with these cars. all my experience in the past has been pre 75 V8s.

why would taking the pipe off make it not run? it should just use atmosperic pressure to pull in air and think its NA for a while.

 

[GVR4592]

When you disconnect the pipe you're bypassing the maf sensor and it won't be measuring the amount of air entering the engine. It will probably start and run, but my guess is that it won't accelerate at all. Do the boost leak test and let us know how it turns out.

 

[GVR4592]

I had a homemade MBC on it which wasnt tapped into the BOV line, but i just got my car back from a shop, and they called my mom and convinced her that wasnt reliable and so they decided to replace it with a real one. And when i just checked, sure enough, it was tapped into about 4 inches from the vacumn port on top of the BOV.

What does this mean?

The bov needs to use it's own source for vacuum, that could be part or all of the problem.

 

[PSI NRG]

Im assuming you dont know how to do a boost leak test or what to use fora boost leak test so I took the time to find you a great web site that will show you how to make one and if im not mistaken how to use it good luck!


http://www.vfaq.com/mods/ICtester.html

 

[oldman]

Novablue454, I know you're confused about what's going on but the situation is as clear as night and day to some of us, I will help you lay it out being as detailed as I can but you need to start following suggestions or else this thread is pointless.

1. Fist you need to understand that air is counted before the turbo so any air lost between the turbo and engine will cause the computer to inject more fuel than necessary because it thinks the lost air is still in the system. This is why you can't just remove the intercooler piping because you will lose the system's ability to count air in order to decide how much fuel to inject.

2. Due to the fact that you're tapping the BOV line, your MBC is bleeding pressure off the BOV line causing the BOV to open when under boost, and since your BOV is vented, this is basically a huge boost leak making your car run pig rich. This can also account for your BOV popping noise.

3. You most likely have other leaks if you've never boost leak tested your car, follow the link provided above and fix your leaks.

4. Now that we know you're running rich when under boost, let's talk about venting. In case if you think venting is cool, it's not. Venting is frown upon amount serious tuners because you're sacrificing performance, reliability and drivability in exchange for sounding cool, it is a serious sign of insecurity and immaturaty towards modding a performance vehicle. The quicker you get over the venting obsession, the better off your car and your wallet will be.

5. So you're boosting along running rich due to leaks, then you blow off and lose even more air running even richer, right about now FPR overrun kicks in and raise your fuel pressure by more than 10psi. Higher fuel pressure mean even more fuel so right about where you let off the throttle, your engine is swimming in unburt fuel hence the popping exhaust, I'm surprised with all these factors added together, your car doesn't just stall and say "F you".

I hope you get the point and start to show your car some TLC, good luck.

 

[Novablue454]

oldman, thank you so much. Im going to try and get the parts to make the tester tomorrow, if i can find a ride.

I have some of the stuff at work, but not all.

thanks for all the replys and for having patience with a newbie to turbos from the v8 world.

 

[Novablue454]

I have a very small boost leak at the lower IC pipe.

Where should the MBC be tapped into? I took the car to the shop with just the MBC I made in it, I didnt add any vacumn line, and they gave me back my MBC with about 2 feet of vacumn hose.

 

[Tony90TSI]

I have a very small boost leak at the lower IC pipe.

Where should the MBC be tapped into? I took the car to the shop with just the MBC I made in it, I didnt add any vacumn line, and they gave me back my MBC with about 2 feet of vacumn hose.

Where did they take the line off of then? Where was the MBC hooked up to previously?

 

[Novablue454]

i know two of the lines that are now in to toolbox were attached to the top of the air filter canister, to a solenoid of some sort i believe. the other one went from the wastegate, to the intake pipe, to somewhere. and the other im not sure of.

 

[Tony90TSI]

i know two of the lines that are now in to toolbox were attached to the top of the air filter canister, to a solenoid of some sort i believe. the other one went from the wastegate, to the intake pipe, to somewhere. and the other im not sure of.

I would do a search on VFAQ.com to find the proper routing for the vaccum lines and basically start all over with them. You dont know what the hell he did to the car in the shop.

 

[Novablue454]

I found 3 leaks, although I dont think that any of them are big enough to cause my problem.

http://www.dsmtuners.com/forums/showthread.php?t=249358

would a bad PCV valve show up in this test?

 

[Tony90TSI]

It shouldnt. as the pressure on the back side of the valve should hold it shut but if its really bad then you would here it leaking under the valve cover.

 

[1Gdsmdriver]

Like gvr4592 said the BOV needs its own source and should never is tee'd into. But the source line should be hooked up to your J-pipe on the output side of your turbo, this is the best place to get your source for the MBC, then we all know where the other line goes to. As for the nipple on the air filter canister that can just be caped off with a vacuum cap and the boost solinoid can have the vacuum lines disconected but leave it pluged in, i believe you have done this already though.

 

[Novablue454]

wait, the J-pipe on the outlet side of the turbo? I have it (now) connected to the metal piece between the air filter snorkel and the turbo. So it should be tapped into the one going to the lower IC piping? I dont recall there being any nipples or vacumn hoses on this, so how should I connect to it?

 

[oldman]

I have a very small boost leak at the lower IC pipe.

Describe in detail how and what you're using for the leak test? How many psi did the boost gauge register during the test and how long did it hold before bleeding down to zero? Did you disable the mbc for the leak test?

Where should the MBC be tapped into? I took the car to the shop with just the MBC I made in it, I didnt add any vacumn line, and they gave me back my MBC with about 2 feet of vacumn hose.

Please explain in detail

1. Which brand and type (ball/spring or bleeder) of mbc.

2. Do you still have the stock 14b with stock intercooler piping? Do you still have the fitting on the turbo outlet pipe off the turbo?

3. How exactly, fitting to fitting, is it hooked up right now?