How does the Brake Booster Solenoid work?

[sapote]

So I've got a an issue related to this right now...NO brakes at all when engine is running. Engine off, I can vacate the booster and pedal goes stiff with hydraulics. Is it actually possible to have the booster fail and create a no brakes scenario? per ChatGPT it is, but that is a wild design if so...

It was working and suddenly went bad, or after you did something?

[sapote]

So I've got a an issue related to this right now...NO brakes at all when engine is running. Engine off, I can vacate the booster and pedal goes stiff with hydraulics. Is it actually possible to have the booster fail and create a no brakes scenario? per ChatGPT it is, but that is a wild design if so...

I think there is no vac delivered by the intake to the booster. Connection to the jet pump is bad?

"Engine off, I can vacate the booster and pedal goes stiff with hydraulics."
This means the booster can is fine.

[fattycharged]

I think there is no vac delivered by the intake to the booster. Connection to the jet pump is bad?

"Engine off, I can vacate the booster and pedal goes stiff with hydraulics."
This means the booster can is fine.

rocked the check valve slightly and there was apparent hissing from the booster, so at least one issue appears to be the gasket. BMW is proud of that sucking jet assembly... which part number for an 01? part number 11617836745 or 11617831663 ? FCP lists both as fitting...

[sapote]

Can you answer post 46?

[fattycharged]

It was working and suddenly went bad, or after you did something?

I have not driven the vehicle in a very very long time, just moved in and out of the garage over the past 18mo.
Only thing recently done is installing SS V1's>Sec3, new motor/trans mounts, spare diff and ds, so I shouldn't have messed with anything on that side.


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[sapote]

rocked the check valve slightly and there was apparent hissing from the booster, so at least one issue appears to be the gasket. BMW is proud of that sucking jet assembly... which part number for an 01? part number 11617836745 or 11617831663 ? FCP lists both as fitting...

While engine running or off? The hissing means there’s vacuum in the booster can as expected. If the booster doesn’t provide power assist then the seal/valve where the pedal push rod enters is bad, blocking air to enter into the rear chamber.

leaking air when you rocking the hose doesn’t mean the seal is bad as it’s distorted by the force.

[fattycharged]

Ok messed with it today again...

With the booster open to atm and engine running, with check valve capped, still have an unstable idle and throw a DME intake man pressure fault.
Removed the jet hose entirely from the fuel rail and no real noticeable leak with the blow/suck test.... So either I have a leaky booster that doesn't leak vacuum, or there is a leak in the jet valve line, or something else I'm not thinking of? I cleared the code multiple times and even engine off the code is thrown....I also swapped out the cheap MAP sensor and wiring with one of the kits from Covid, so possible that is throwing the code, either way it was present prior to that, along with lean mix

Ordered a booster to have on hand for install once I pressure test the vacuum with my latest Amazon purchase of a smoke tester and caps.

[fattycharged]

$50 Amazon purchase worth its weight. MAP sensor leaking heavily and the other main culprit is AT injector 6 on the rail, pouring smoke.

So for future anyone having this issue, haven't solved it quite yet till I pull the rail and figure out what to do with this MAP sensor. I did try and replace the o-ring on the MAP already with no luck, likely too small but all i had lying around from a shock rebuild.

I'd post a video but don't know where to host quickly



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[fattycharged]

6 looks noticeably bent to me…


found my culprit on 6

and 3


sorry yall, realize i've turned this thread into my journal…


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[jayjaya29]

Still interested if fixing the vacuum leaks resolves the brake pedal issue.

[fattycharged]

Still interested if fixing the vacuum leaks resolves the brake pedal issue.

I've got a local hydraulic supply shop I am going to stop by to see if they can supply them, otherwise I won't have them till next week through ECS


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[fattycharged]

should get it fired back up tonight and will update on booster function


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[fattycharged]

No dice...no more noticeable vacuum leaks after new air rail o-rings, but no brake booster either.

[bigjae46]

Have you tested solenoid between the booster and intake manifold. Maybe unplug it and see if the brakes stick on if you rev the motor.

[fattycharged]

Have you tested solenoid between the booster and intake manifold. Maybe unplug it and see if the brakes stick on if you rev the motor.

I will give it a shot, but I think I have tried that. Valve clicks with key in start position when I unplug it and plug back in, so I assume functional.
After clearing up vacuum leak at the air rail and almost completely at the MAP sensor (still a small leak...) I still have idle issues, engine is running rough after cold start cycle, it gets worse when I hit the brake pedal.