stuttering under boost

[94Talon2]

I can't figure out what my problem is. When I drive my car hard for the first 5 minuets (once it reaches normal operating temps) it feels fast and smooth. Then after 5min it stutters and hesitates under boost, and is much slower. What could my problem be? I have a rebuilt engine, basically a stock tsi. I was thinking my bov could be slightly open under boost(but I think that would cause me to have lower boost levels)

Thanks.

 

[1G/TS-ituner]

it could be a few things but i would try replacing your 02 senser, then check to make sure your MAS is functioning properly, that and check for boost leaks. cracks in the hoses, make sure all of them are tight remember those hoses expand quite a bit under boost.

You said after it warms up it starts to studer so my first guess is the O2 is getting funky on you when it heats up, and your MAS could be bad if the senser itself starts off breathing in cold air then the heat from the motor throws it off due to it just not doing its job....you definately need an constant loging system if you want to know for sure. my SAFCII takes cars of anything i need to monitor on the motor.

 

[CanadianTSi]

Change your Plugs/Wires.

 

[94Talon2]

plugs and wires are new. I did a boost leak test, I'll check out the o2, thanks for the help

 

[oldman]

I did a boost leak test

How much psi and for how long was the system able to hold?

 

[Coup D E'Tat]

The ECU does not use the O2's under WOT.

 

[94Talon2]

How much psi and for how long was the system able to hold?

i was only able to get 10psi, my air pump is a peice of crap, I had a small vacume leak but I fixed it. The pressure slowly declined.
Yesterday I drove with my bov vented, the car was running like it normaly would, after about 10min I would hit fuel cut at 3-5psi. This is why i think it's the bov, because it just keep reciculating, and this is why I don't get fuel cut when the bov is recirculating.
What do you guys think?

 

[oldman]

i was only able to get 10psi, my air pump is a peice of crap, I had a small vacume leak but I fixed it. The pressure slowly declined.
Yesterday I drove with my bov vented, the car was running like it normaly would, after about 10min I would hit fuel cut at 3-5psi. This is why i think it's the bov, because it just keep reciculating, and this is why I don't get fuel cut when the bov is recirculating.
What do you guys think?

Not nearly good enough, the desired test result would have been around 20psi for at least 30 seconds. 10 psi means you have more leaks to discover. Don't vent your BOV.

 

[94Talon2]

I was only venting the bov to test it. I know I need more pressure, but i'm having problems at low boost too.

 

[1fast97gsx]

you have a boost leak ... pressurize it up to about 25 psi and see how long it will hold.

 

[94Talon2]

How long should it hold, how gradualy will it drop?

 

[1fast97gsx]

mine holds for 3 seconds or so ( maybe a tad less ) and then bleeds off 1 psi per second.

 

[94Talon2]

No Boost leaks! I pressure tested the intake today, However air was coming out of my catch can filter is this normal?

 

[oldman]

No Boost leaks! I pressure tested the intake today, However air was coming out of my catch can filter is this normal?

Read through this thread, come back and ask questions if you have any.

 

[94Talon2]

Wow! that is a lot of reading. It sounds like I have a turbo seal problem, because my turbo used to leak oil into the intake. I did some research, and many turbos blow seals due to crank case presure. It turns out my crank case breather was cloged causing too much pressure. Last week I made a catch can and the turbo doesn't seem to be leaking. The only thing that doesn't make sence is the fact that my problems only occur when the engine is hot. The rubber should seal better at high temps, so this isn't really making much sense to me. I'll see if I get a differance in boost drop testing it from the licp vs the turbo.

However: maybe my problem has nothing to do with engine temp, maybe the hotter the turbo, and the more it spins wich opens up the seals causing a leak.

Thanks oldman!

 

[oldman]

Wow! that is a lot of reading.

Good job for getting through it, I can't even go back and read it anymore, it hurts head.

I did some research, and many turbos blow seals due to crank case presure. It turns out my crank case breather was cloged causing too much pressure.

Exactly how I did mine in, frozen catch can filter. Took out my turbo and valve seals, I was lucky my rings held up.

It sounds like I have a turbo seal problem, because my turbo used to leak oil into the intake.

Don't guess, go through every step in that thread and you will get your answer. Make sure you don't have multiple problem like I did.

Thanks oldman!

You're welcome and good luck.

BTW Make sure you remedy the catch can situation. If both pcv and breather are routed to the can, make sure

1. pcv is hollowed out or replaced with a straight fitting, pcv is designed to be sucked open by vacuum on the intake side not pushed open by the pressure on the crankcase side.

2. The catch can itself has proper venting capacity.

 

[94Talon2]

Ok, I just pressure tested from licp, It holds 20psi no problem, and held boost quite well, droped 1psi every 2 seconds from 20-10psi and then droped 1 psi like every 4seconds from 10-0psi. So this tells me my turbo seal is leaking a bit, the pressure droped faster when I pressure tested from the turbo. However: I still had air leak from my catch can filter.
My compresion is good 175psi in all 4.
The engine is rebuilt with new head, valve seals should be good (car doesn't blow any blue smoke)
PCV and crank case breather are routed the a catch can.

 

[oldman]

How much psi were you able to build at the turbo inlet this time? You said you were only able to build 10psi the first time, what did you fix that you're not telling us? As long as you are not smoking at anytime you should be fine.

 

[Defiant]

plugs and wires are new.

What plugs, and what gap?

 

[94Talon2]

No Boost leaks! I pressure tested the intake today, However air was coming out of my catch can filter is this normal?

I got up to 20psi, boost droped fast, 2psi every second.

What plugs, and what gap?

NGK's .28 gap, Accel wires. Plugs are about 2 months old, I looked at them yesterday, they look good, good combustion. The wires are about 2 years old.

 

[oldman]

I got up to 20psi, boost droped fast, 2psi every second.

That is not bad so what did you fix that changed from 10psi to 20psi? Is your stuttering problem still there. I also want to point out again that make sure the pcv has been hollowed out or replaced with a straight fitting. Pay very close attention to your crankcase ventilation, I have seen many (including myself) having excessive crankcase pressure issues doing a lot of damage. If you're venting both to a catch can make sure it's done right before you do damage to turbo seal, valve seals and rings.

 

[94Talon2]

That is not bad so what did you fix that changed from 10psi to 20psi? Is your stuttering problem still there. I also want to point out again that make sure the pcv has been hollowed out or replaced with a straight fitting. Pay very close attention to your crankcase ventilation, I have seen many (including myself) having excessive crankcase pressure issues doing a lot of damage. If you're venting both to a catch can make sure it's done right before you do damage to turbo seal, valve seals and rings.

I didn't change anything, I was using a bike pump. I used an air compersor for the last 2 tests. The first test was hooked up to the turbo and that's were I saw 2psi drop per second, and the second test was from the licp, and I lost 1psi like every 2 seconds. I'll replace the pcv with a straight fitting, what size? 12mm?

Yes I'm still having the same problem, not responsive under boost, when engine HOT.

 

[oldman]

I'll replace the pcv with a straight fitting, what size? 12mm?

1/8 npt, you will need a 1/8 npt tap to run it through the hols as the pcv thread pitch is slightly different.

Yes I'm still having the same problem, not responsive under boost, when engine HOT.

Was any of these pressure tests perform while the car is fully warmed up? If not, do one. If it was done already with the car warmed up, with good compression number and correctly gaped plugs, I would then suggest doing the following.

1. Test run with your mbc/bcs bypassed. If problem solved, mbc/bcs is probably your problem. If problem persists, go to 2.

2. Test run with actuator bypassed, this will result in all out boost so feather throttle so to keep boost at around what your fuel system can support. If problem solved, you have issues with the actuator. If problem persists, go to 3.

3. Check for any exhaust leak (with the car warmed up) before o2 housing. If everything checks out up to this point, I would suspect the turbo.

 

[94Talon2]

All tests were done when car was warmed-up.

"1/8 npt, you will need a 1/8 npt tap to run it through the hols as the pcv thread pitch is slightly different."
wait i'm not sure if I understand. So I replace the pcv valve, with a 1/4 copper fitting from a hardwear store?




Soon as I'm done work I'll go do that. I really appreciate all the help, You're a great asset to the DSM community.

 

[oldman]

wait i'm not sure if I understand. So I replace the pcv valve, with a 1/4 copper fitting from a hardwear store?

Yes, with 1/8 npt thread pitch or you can drill out the center of the pcv you already have.