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Brake Booster Troubleshooting

Old 06-21-18, 05:05 PM
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Exclamation Brake Booster Troubleshooting

Recently I removed my intake manifold to replace my knock sensors, wiring harness, rebuild the starter solenoid, and replace the injector O-rings. Once I got the car started again I began to have some issues. At first I had the Check VSC, VSC OFF messages on the dash but replacing the Engine Coolant Temp Sensor that I had busted cleared up that issue.

Unfortunately the problem I'm still experiencing is that the brake pedal has almost no travel and the BRAKE light remains on even after the parking break is released. Vacuum hose seems to be on there good. I had a few codes but after I cleared them with techstream none have returned.



Failed the first two test from the above picture. I haven't inspected the vacuum check valve but will momentarily.

I just don't understand how the brake booster seemed to work fine before I removed the intake and then suddenly failed once I got the intake back on. I've gone over all the plug and hoses that I'd removed and all seem to be secured in the right locations.

Anyone got any light to shed on my issues or should I just go ahead and start looking into replacing the Brake Booster assembly?
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Old 06-23-18, 10:24 AM
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Do you have vacuum in that booster hose with the car running? Yes, it will run like she-ot with the hose disconnected, but if you have someone start the car and you keep your thumb over the end of the hose, it will idle normally and you can get a feel for how much vacuum the engine is pulling through that hose.

That's where I'd start...
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Old 06-23-18, 10:45 AM
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Originally Posted by 2KHarrier View Post
Do you have vacuum in that booster hose with the car running? Yes, it will run like she-ot with the hose disconnected, but if you have someone start the car and you keep your thumb over the end of the hose, it will idle normally and you can get a feel for how much vacuum the engine is pulling through that hose.

That's where I'd start...
Yes when I put my finger over the hose there was enough vacuum that I felt my finger getting sucked in. Couldn't say if it's weaker than it should be or not.
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Old 06-23-18, 11:34 AM
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Originally Posted by SlkySmooth View Post
Yes when I put my finger over the hose there was enough vacuum that I felt my finger getting sucked in. Couldn't say if it's weaker than it should be or not.
Well, without using a gauge, we can't be 100% sure, but I would have to assume you've got a problem someplace else. That should be plenty of vacuum to power the brake booster. Make sure the brake pedal moves freely (or as free as possible) with the engine off. It's just weird that all of a sudden you've got a new problem...
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Old 06-23-18, 11:49 AM
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Originally Posted by 2KHarrier View Post
Well, without using a gauge, we can't be 100% sure, but I would have to assume you've got a problem someplace else. That should be plenty of vacuum to power the brake booster. Make sure the brake pedal moves freely (or as free as possible) with the engine off. It's just weird that all of a sudden you've got a new problem...
The pedal seems to be just as stiff when the engine is on or off. I'm just as confused where this new problem came from it's the onlyonly thing stopping me from driving the car right now.
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Old 06-23-18, 09:37 PM
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Two votes for getting a real vacuum gauge on it.
Any chance you had a plug or paper towel or something to plug the hose or manifold and left it in?
Brake boosters are pretty hardy.
It seems like something was missed and is not as it was.
The engine runs and has vacuum. If the vacuum is available at the booster, you would hear a huge leak if it failed. I'd say it has no vacuum.
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Old 06-24-18, 09:11 AM
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I think autozone has a gauge I could rent. What does the vacuum need to be on the hose that goes to the brake booster?
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Old 06-24-18, 09:38 AM
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At average altitude and normal idle, you should be able to see 17-21 inches of vacuum.

Not sure if this will help, but here's some very basic info on the system;



I tend to agree with 2013FSport. Something changed when you did the knock sensor and now you're seeing the results of that change.
Let us know what the gauge reading states, and we'll go from there...

If you have access to a vacuum pump, you could use that on the booster to see how the brakes feel, then you would be able to isolate the problem.

It sounds strange, but another car could be used as the vacuum source, with a long enough hose...
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Old 06-24-18, 11:45 AM
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Well I borrowed a gauge from autozone, put it on the line going to the brake booster the needle didn't move at all. I guess that means I'm not getting enough vacuum I'm also noticing thethe car idling over 1k when I start it up. Not sure how to track down the a leak though
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Old 06-25-18, 06:14 AM
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Originally Posted by SlkySmooth View Post
I'm also noticing the car idling over 1k when I start it up. Not sure how to track down the a leak though
​​​​​​
Grab a can of starting fluid and spray (in short bursts) all the areas you had opened up. All the surfaces that mate to another surface and hose connections. When the engine draws in that ether, it'll change the RPM for a moment and you will have found your leak, IF you have a leak...

Do it in short bursts though, not like you're spray painting a fender...

Another thing that you can do is use a scanner with "Live Data" capabilities and watch the short term and long term fuel trims, known as STFT and LTFT. They should stay within 3% of 0 either side (+ or - 3.0%) If it goes too far into the positive (+10.0% to +25.0%) then you definitely have a vacuum leak somewhere and the engine is trying to compensate for it by adding more fuel, hence the higher idle speed.

Here's a good tutorial on Fuel Trim;

http://www.easterncatalytic.com/educ...agnostic-tool/
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Old 06-25-18, 06:18 AM
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Originally Posted by SlkySmooth View Post
Well I borrowed a gauge from autozone, put it on the line going to the brake booster the needle didn't move at all. I guess that means I'm not getting enough vacuum
The needle should have moved a little, though. Depending on how sensitive the gauge is, even a few inches of vacuum should have been enough to register on the gauge. You stated that your thumb over the hose could feel the draw of air, so you should have some vacuum there. And of course, with the booster hose disconnected, the RPM will rise considerably..
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Old 06-25-18, 08:06 PM
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I just watched a clip of a vacuum/fuel pressure gauge in action and I'm pretty sure the one I rented is only for fuel pressure.

I tried something similar to what you described with propane rather than starting fluid, but I wasn't very patient or thorough with it as I had to leave for work. The high idle I noticed Is without disconnecting any hoses.

I'm just now having somewhat of an "epiphany" and remembering that I noticed the PCV hose was cracked pretty good long before I took this project on. Perhaps the crack grew while I was moving things around. I ordered a new hose from the Toyota dealer down the street and a new PCV valve off amazon. I'll be crossing my fingers that the PCV hose is the culprit and I won't have to do too much more diagnosing but I'll still plan for the worst and read up on that link you sent me about fuel trim. I think I may as well try finding an affordable vacuum gauge while I'm waiting on the two parts.
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Old 06-26-18, 04:01 AM
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Glad to hear the update. Keep us posted as to what you find.
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Old 06-26-18, 12:39 PM
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I've got some electric blue silicone tubing laying around from another car Im hoping will make a good replacement for a few of the vacuum hoses in the meanwhile.

Wish I could find a similar photo for my engine.
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Old 06-27-18, 08:42 PM
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Alright, so I got a vacuum gauge and the parts I mentioned in the mail today. Hooked it up to the hose going to the brake booster and what do ya know it went straight to 20 psi! I suppose that's a bit of good news at this point that I don't need to keep chasing a vacuum leak.

Does anyone have a professional/amateur opinion on this matter?

I'm thinking this must mean the problem is in the brake booster? Perhaps it's out of alignment?
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