I have been chasing down a hard brake pedal issue. th car has an L61 with stg1 compcams, intake 4-2-1 header, msd ign. the car had been parked for awhile and it thought maybe something had tried to seize up on my from being parked, so I checked my calipers and lubed all slider pins, still hard a pedal. next i checked the booster check valve and its good, air only goes one way, and there is the normal suck sound of the vacuum breaking when the line is removed. I got a vacuum gauge and hooked it to the manifold where the purge valve hose normally goes. i get a reading of 8-10" with a steady fast flicker, goes almost to zero when accelerated, if I move the gauge to the FPR with a tee in the line it goes to 10-12" still with the fast flicker. i think the fast flicker is due to the hotter cam, could it be late valve timing? I thought i misaligned something before and redid the timing 10-2-5, number one piston at TDC. throw all your ideas out there, I'd like to get this resolved before it gets to cold for me to work on it as I don't have a garage, and its already starting to cool off.

Checked for vac leaks? Sounds like a small vac leak combined with having a bumpy cam.


1994 Saturn SL2 Home Coming Edition: backup car
2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
1995 Mazda Miata R-package Class=STR
Sponsored by: Kronos Performance

WPI Class of '12 Mechanical Engineering
WPI SAE Risk and Sustainability Management Officer

Leafy (Club Jeffie FEA man) wrote:Checked for vac leaks? Sounds like a small vac leak combined with having a bumpy cam.

Truth... is the engine idling okay?

I would hook a vac pump to the booster and apply vacuum and see if it holds. You can also check the pedal at this time once you get 20inHg in it.

Ignition timing has a drastic effect on vacuum... I would double check sensors that could bring about a timing issue with the engine as well.

Never check the EVAP port for vacuum... it is a calculated oriface and will always give a false reading.



Buildin' n' Boostin for 08' - Alex Richards

Pull the hose out of the booster and plug it with your thumb. See if this increases your vacuum at idle. As you accelerate the engine vacuum will become less and less, so dont pay any attention to that.

If that does raise your vacuum up, Id say the atmospheric port in your booster is dinked. If that doesnt raise your vacuum up, plug the hose back in.

Grab a can of brake clean and spray over all the possible areas of a vac leak:

ie: manifold gaskets, vac line etc.

If the engine idle raises when you spray over a certain area, you've found your vacuum leak.

Good luck.

Jeff Wybrow wrote:Grab a can of brake clean and spray over all the possible areas of a vac leak:

ie: manifold gaskets, vac line etc.

If the engine idle raises when you spray over a certain area, you've found your vacuum leak.

Good luck.

This will not work on our vehicles. A Vac leak on our vehicles raises MAP value and has an effect on fueling. You will not see any difference hitting any vac leak with brake or carb cleaner.



Buildin' n' Boostin for 08' - Alex Richards

It still should make the idle go up for a second as you introduce more oxygen and fuel (most solvents in those cleaners have extra oxygen in them).


1994 Saturn SL2 Home Coming Edition: backup car
2002 Chevy Cavalier LS Sport Coupe: In a Junk Yard
1995 Mazda Miata R-package Class=STR
Sponsored by: Kronos Performance

WPI Class of '12 Mechanical Engineering
WPI SAE Risk and Sustainability Management Officer