idle disruption: brake booster?
07-11-04, 12:24 AM
#26
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Sorry; haven't had the time to check the check valve or pull a vacuum on it; will try to do so today. But thinking about it, the (fairly) low idle vaccum on the rotarys is alot like pistons with killer cams; alot of drag cars use add-on vacuum cans. Maybe a little more "vacuum volume" would help this problem?! Hmmm; add to "to-do" list of things to try....
Sanspistons (and sanstime...)
Sanspistons (and sanstime...)
07-11-04, 04:21 PM
#27
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Re: idle disruption: brake booster?
Originally posted by bouis
I realize that a momentary idle drop is normal when braking, but if I mash the pedal quickly and repeatedly while idling I can nearly stall the engine. I'm not sure if this is normal on a first gen or not. Anybody?
I realize that a momentary idle drop is normal when braking, but if I mash the pedal quickly and repeatedly while idling I can nearly stall the engine. I'm not sure if this is normal on a first gen or not. Anybody?
By pumping the brake pedal you are introducing a huge vacuum leak to the engine.
Remember that the brake booster works off of vacuum! There's a big diaphragm in the can, connected to the brake pushrod. Vacuum on both sides. When you apply the brakes, you allow air into the backside of the booster, and the pressure pushes on the diaphragm which pushes on the pushrod which assists your braking. When you let off the brakes, vacuum goes back into the rear section.
But vacuum isn't really going IN, the engine is sucking the air OUT.
So what happens when you pump the brakes? You're letting air into the booster when you push down and when you let up that air goes into the engine. Pump pump pump... essentially a vacuum leak!
07-11-04, 04:37 PM
#28
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Originally posted by bouis
I haven't been able to stall the engine, but it seems close -- sub 500 rpm. It does seem to hold vacuum for at least a day or so as evidenced when removing the hoses.
I read the FSM's section on the brake booster and I'm going to try all the tests, as well as the check valve, tomorrow. It doesn't pose a drivability problem, but I want to be thorough.
I haven't been able to stall the engine, but it seems close -- sub 500 rpm. It does seem to hold vacuum for at least a day or so as evidenced when removing the hoses.
I read the FSM's section on the brake booster and I'm going to try all the tests, as well as the check valve, tomorrow. It doesn't pose a drivability problem, but I want to be thorough.
Idle drop is not normal for a sinle squish.
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