Hey guys, it's been years since I've posted on here because my GTA has been parked since 2002. I'm trying to resurrect it now, and I'm having trouble getting it to pass inspection because they say my brake pedal is to firm due to lack of vacuum (and it takes all my strength to hold the car still at idle, it's not just the shop being picky).

Problem is, I can't find a vacuum leak anywhere. I replaced the line running from the plenum down to the cruise and the little vacuum ball in the fender because it had deteriorated, but all the rest seem fine. The PCV valve is not stuck open, and I don't have any open ports anywhere.

Also, it really only does it when it's fairly cold after startup and is still in Open-loop mode because the idle is erratic then. When it settles down in closed-loop it seems OK.

And I know, someone is going to say just take the car in when it's hot and in closed-loop - but the car wasn't like this when I parked it, something has changed, and I'd like to figure out what.

Any ideas?

Also, does anyone have a picture or diagram of where all the vacuum lines are supposed to hook up on a stock engine? Just so I can double-check everything. Thanks.

 

I guess I should add my list of mods:

350 w/ LT4 Hot Cam & Edelbrock 6085 heads
stock TPI intake
30 lb SVO Injectors
AFPR
SLP 1 3/4" headers (w/o AIR)
removed all smog equipment
custom PROM by me
lot's of other little stuff that I can't remember now

 

The brake booster may be bad. Disconnect the hose to it and connect a vacuum gauge. If it has more than 12 inches of vacuum available, replace the booster.

 

OK, took me a while to get around to it, but I finally got a vacuum gauge on the engine, and I am getting exactly 12" at idle. Do you think I should replace the brake booster, or work on ways of increasing the vacuum at idle (raising the idle, etc.)?

 

Hmmm. Was that in park or drive?
I wouldn't change the booster if it worked before the LT4 cam went in.
Since you do custom prom, I would try more timing advance at idle to try and bring it up. If you have winaldl check the booster by comparing the idle air setting with the booster plugged off. It should be the same as when constant brake pedal pressure is applied with it hooked up.
Also I didn't notice a stall converter in your mods. If the vacuum is too low in drive you may need one.

 

That was in park. All of the mods shown above happened at once as it was a crate motor that I dropped in (has about 35k miles on it now), and the brakes worked fine for all of those miles even with the LT4 cam. It's only since the car has been sitting for years now that I'm having an issue.

As far as the custom PROMs go, I still have all my tuning files and stuff, but I can't find my PROM burner anywhere and it's driving me nuts! I've torn my house apart but can't find it anywhere. So I'm kind of trying to feel out if I have any other options before I go and buy another burner again if I have too. I'll try scanning the car and IAC setting as you suggested.

Also, I do still have a stock stall speed converter.

 

That changes everything. If you had good brakes with that setup then the booster may have bitten the dust.
Any chance of getting one from the J/Y?
Check the vacuum with it in drive. 12" in park seems low even with the LT4 cam...

 

I don't know of many J/Ys around here, but a reman'd one from Advance is $88 - that's not too bad. Before I go buy it though, if it was bad, would it show it only at idle, or all the time? Cause the brakes are fine when I'm driving the car. It's only when the engine drops to idle that they get stiff. And I should add, the brakes have always been a little weaker at idle since the crate engine was put it (but not nearly like they are now), and I've always figured it's because I've never gotten the idle tuned in right in the computer. It idles rock-steady in gear, but in park and nuetral it's excessively rich (exhaust smell). I really wish I could find my PROM burner and try some stuff before I buy anything else.

 

OK, I checked the vacuum again in drive today and it was only 9", so I'm going to hold off on the booster for now. I've noticed that Summit and Jegs both sell vacuum reserve canisters with check valves to help retain vacuum for brakes on cars with big cams. I'm thinking I can duplicate the same thing if I put a tee in the booster line and run the branch to the factory vacuum canister, and put a check valve right at the manifold. What do you think?

 

That will definately help. Be sure and post a picture of where you mount it. I'd like to put one on mine but can't find a place. I got good brakes for 1 pump; for me: no problem, someone else.?.. (224°@.050 w/108° LSA)