HRHohio

Hi guys,

Looking for some help here. So the other day, I finally get my setup running pretty good, I thought.
Setup:
2002 Convertible Z28, A4
Stock bottom, LS9 Cam, Stock Heads, etc
Rear Mount Turbo, 76mm, Intercooler, Snow Methanol, NO BOV (Automatic).

I just rearranged my charge pipe (went SD, removed 85mm MAF, removed BOV).

So I'm driving, and I notice that the throttle stays open when the car gets into boost when at WOT. I take my foot off gas, pedal stays down, I **** pants.

This happened at the track on Friday during burnout, I'm standing on brake with both feet, car wont stop. To say the least, I did an NHRA Top Fuel burnout... put in in reverse.... back up 30 ft... then do my run. Have to put car in neutral to get throttle to disengage.

Today, I swapped throttle body with friend, stock TB. No change.

Is it possible that because I am not running a BOV, my turbo is overpowering the TB spring and not allowing it to close? Lots of built up compressed air between the rear mount turbo and the TB.

The only way to get the car to stop is to bump it into neutral.

I'm freaked... my first thought is to get a damn BOV back on. Was hoping to hear from someone who may have heard of something like this happening before. (Side notes: its not the floor mat, that's been taken out and it still happens. It does not do this when in park or when the engine is off. The throttle cable feels fine, smooth. Unable to reproduce when not in boost. Feels like cruise control kicking in. Happens when boost hits 2psi or more. My max boost is set to 8psi.)

Open to ideas... Thanks!

MadIceV8

iTrader: (12)

Make sure the spring on the TB is wound up tight.

denmah

iTrader: (2)

or add another spring.

ive never had this happen even with small motors and 25lbs of boost

is it returning smoothly and slapping shut

itsslow98

iTrader: (18)

Why no BOV?

Sweet_SS

I'm curious as well. Why no BOV?

HRHohio

Was told not absolutely necessary (automatic car).

HRHohio

Yes, returns smoothly and slaps shut. Like I said, feels like the cruise control is kicking in. When car is off, returns fine all the time, when in park/neutral...rev to 5000 no problem, no sticking. Doesn't stick any other time, only when I get into boost on the road.

When you say, "small motors and 25lbs boost..." did they have BOV? I'm thinking my system is flowing so much air and no place to go, its pushing TB open.

Rationale: 8lbs boost > TB spring tension.

Ever heard of such a thing?

js2fst

iTrader: (12)

Check your foot pedal sensor I had my vette do it

cyipher

iTrader: (1)

Put a bov on it, even with a auto your killing you turbo everytime you come out of boost (compressor surge) as far as your sticking throttle I'd say thats related to having no bov too.

HRHohio

Interesting...Can you elaborate a little? What am I checking for? Never heard of a "foot pedal sensor". Do we have them on '02 Camaro? What's it look like, where is it? How did you know yours was bad? Why would this happen only in boost?

Thanks!

HRHohio

Yeah, I was thinking of putting it back on anyway (in the process of rearranging my charge pipe layout), but was rushed and didn't get a chance to do it yet.

Right now, I'm just trying to connect the dots and (for educational purposes) understand why the throttle was staying open. Would like to know if that is the actual cause (no BOV) or not.

BottleFedZ346

iTrader: (17)

LOL!

Tell that to Denmah, 10k on that $200 ebay GT45 and was still going strong without a BOV!

OP i hope you figure out the issue, best bet is to stay out of boost until you get another BOV welded back on and see if it changes!

jtotheizzo

My first inclination was to say "yeah of course it is the BOV because that is what you changed." But the more I think about it the more I would lean towards how is the BOV going to activate if the throttle plate is not closing and creating vacuum in the manifold and a boost spike in the charge pipe? or am I completely out to lunch on my BOV theroy.

You could always build\use a boost leak tester. Pressurize the manifold and snap the throttle by hand to see if you can reproduce. If you can reproduce try disconnecting the cable and see if it goes away. The fact that two TB's did the same thing makes me lean towards bind in the cable.

js2fst

iTrader: (12)

No it was a corvette

Atomic

iTrader: (37)

Is it a cable tb or electronic tb?

obZidian

iTrader: (2)

So your issues are coming up AFTER you deleted the MAF, went SD and removed the BOV? Who tuned it for you? Perhaps its in the tune.... there are a few tables that can help fix that issue if in fact it is nothing mechanical.

HRHohio

Thanks. Yeah, kinda freaks me out when the car takes off with a mind of its own. Boost only in controlled environments, hand close to the keys... lol


I think it would have to do more with a combination of boost pressure and flow, vs. boost alone. Without the car running, the manifold pressure would eventually equalize to the pre-TB pressure, if that makes any sense. I'm trying to imagine how the TB opens and the airflow across it. Potts ported TB by the way.


Cable TB.

Can't understand why it would bind under boost and not any other time. Next step is to disconnect a coupler and see if it happens N/A at WOT.
The other thing I can't understand is why is it when I put it into neutral, the pedal pops back up and releases. ??? Haven't had to switch off the ign yet, just bump it into N....

HRHohio

Actually, I went from MAF to SD before I removed the BOV. Ran fine. Then a couple weeks later, when I got the time to do it, I pulled off the MAF and BOV, put a straight 3" in place with 2 90 elbows, tapped in the IAT and Meth/Water inj. (no change to the tune, was already running SD for about 2 weeks with the MAF still inline but not connected). After all that, that's when the problems started. (Local tuner)

Chris@CBR

Somebody buy this guy a beer!
You are 100% correct, The BOV can not have any affect on this, it only works when the throttle is closed.

Check and make sure that your throttle body only opens 80-85 degrees.
I have seen this more than once.

Every time it was because someone tweaked the throttle bracket until the
throttle blade was dead flat at WOT.

jtotheizzo

I am assuming that when you say the pedal sticks to the floor that means it is physically lying on the floor. This says to me it is a mechanical problem. not an issue with the tune.

This makes a lot of sense to me because if the blade is only at 80-85% then the air rushing in does in fact help it close. If it were 100% open you lost that effect.

My thought on this if it were in fact the boost holding it open is it is possible that the spring has the gumption to overcome the bind without the added stress of the boost but lacks the gumption with the boost.

Assuming it has cruise control just for grins disconnect the cruise control motor and see if it still happens. It would be probably one of the weirdest things I have seen but hey its order of elimination here. But with that said I don't recall if my pedal moves with the cruise control. Anyone else on that?