Stall under hard braking and MAP line is clear - ZR-1 Net Registry Forums

1991 Corvette ZR-1 · 03-16-2023

So I was thinking this is either the MAP and associated tube or the brake booster assembly. Out for a drive recently, I used maybe 3/4 of what one would use aggressively braking, so not quite standing on the brakes and the car stalled.

I pulled the MAP sensor hard line and it was clean. Years ago when applying any level of braking at low speeds even gently would cause a stall condition. A poor choice in replacement tubing by someone from plenum to MAP was the culprit then.

I have no way to check if this is the actual MAP sensor directly causing an issue. So the next place my thought process goes is to the booster having a vacuum leak. The brakes on this car have never been anything to write home about. Even after replacing all four rotors and pads with a Stoptech kit and full fluid flush, the braking felt the same as the old tired rotors and pads. So I am wondering what if my booster has been bad from the start.

This would also explain why my idle jumps 75-100 rpm from stoplight to stoplight. This has always bugged me how could the car could have a vacuum leak that just decide to not leak until 15 minutes into a drive, then start, then stop again and repeat several times through the drive. Before anyone asks, Marc had already rebuild my TB, so I know that?s not causing the idle issue.

So this is a ZR-1 specific booster with dual diaphragms compared to the single diaphragm version used on standard C4s. How screwed am if the booster is indeed bad? I was looking into a way to bench test it.

Why is this a dual diaphragm? Is this related to the vacuum required for the secondaries? The FSM does not go into the details of why there are different boosters.

03-16-2023	#1
1991 Corvette ZR-1 Join Date: Sep 2018 Location: Florida Posts: 305	Stall under hard braking and MAP line is clear So I was thinking this is either the MAP and associated tube or the brake booster assembly. Out for a drive recently, I used maybe 3/4 of what one would use aggressively braking, so not quite standing on the brakes and the car stalled. I pulled the MAP sensor hard line and it was clean. Years ago when applying any level of braking at low speeds even gently would cause a stall condition. A poor choice in replacement tubing by someone from plenum to MAP was the culprit then. I have no way to check if this is the actual MAP sensor directly causing an issue. So the next place my thought process goes is to the booster having a vacuum leak. The brakes on this car have never been anything to write home about. Even after replacing all four rotors and pads with a Stoptech kit and full fluid flush, the braking felt the same as the old tired rotors and pads. So I am wondering what if my booster has been bad from the start. This would also explain why my idle jumps 75-100 rpm from stoplight to stoplight. This has always bugged me how could the car could have a vacuum leak that just decide to not leak until 15 minutes into a drive, then start, then stop again and repeat several times through the drive. Before anyone asks, Marc had already rebuild my TB, so I know that?s not causing the idle issue. So this is a ZR-1 specific booster with dual diaphragms compared to the single diaphragm version used on standard C4s. How screwed am if the booster is indeed bad? I was looking into a way to bench test it. Why is this a dual diaphragm? Is this related to the vacuum required for the secondaries? The FSM does not go into the details of why there are different boosters.