Possible Vacuum Leak at Brake Booster

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finazzoty

Well-Known Member
For months now I’ve been trying to chase down an idle issue that seems as though it must be getting caused by a vacuum leak and is thus causing a loss in negative pressure to my fuel regulator.

The other day, I noticed a hissing noise coming from my brake booster. After some fiddling, I discover the hissing goes away when you pull the brake pedal towards the driver. What could be causing this? The brake booster is brand new. I’m wondering if this is the leak that is causing my idle issue
 
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G Atsma

Goblin Guru
If you hear hissing from the booster, you DO have a vacuum leak. A new booster CAN be defective, but check all around it first.
 
Ross

Ross

Goblin Guru
The brake booster is suppose to release vacuum (air) when the pedal is depressed. Maybe your booster-to-pedal distance is out of adjustment.
Try shortening the pushrod, or spacing the booster away from the pedal. I think my booster has spacers.
 
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finazzoty

Well-Known Member
So the hissing/leak is occurring when the pedal is not depressed at all. How would I go about adjusting the pushrod? Mine just slips over the little peg on the brake pedal. No spacers or anything so far as I can tell
 
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finazzoty

Well-Known Member
@Ross So I gave the shim idea a try and unfortunately it is still leaking. And @Goblinfanclub1234 I don't think it is the check valve as the hissing seems to be coming from where the pushrod meets the seal that is attached to the body of the brake booster. Seems like it may be a defective booster, which would be highly irritating, considering it is brand new.

EDIT: Could this be tested by disconnecting the line from the intake manifold and plugging that hole? -- Then try to crank
 
duthehustle93

duthehustle93

Active Member
It's very possible that an aftermarket unit is bad out of the box. Two easy ways to verify the vacuum leak would be to pinch off the vacuum line (you can also remove the line and capping the I/M as you proposed) or fog propane or brake cleaner into the area that you suspect the vacuum leak... if your idle changes then you have a vacuum leak. You should be able to run a long vacuum line and do this as a bench test to verify that the booster on it's own leaks.
 
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Gtstorey

Goblin Guru
If you have a mighty vac type vacuum pump, you can apply vacuum to the line and see if it holds.

Very much possible a new unit leaks. Probably more likely than a used unit.
 
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finazzoty

Well-Known Member
Well here is the discovery:

I'm still convinced there is a vacuum leak at the brake booster (due to the hissing noise), but it is so insignificant that it is not causing the problem, because the strange idle surging still occurs even when I disconnected the line and capped it off. Waiting to hear back from ZZP as to how they set up the channel for my wideband in HPT and maybe this will provide some useful information as to what is causing this issue.
 
Ross

Ross

Goblin Guru
I had a vacuum leak where the DF vacuum line attaches to the brake booster. There is a rubber line that connects from 1/2" tube on the brake booster, down to a 1/4" vacuum line from the intake. I fixed it by torquing down on the hose clamp that has to shrink the hose to 1/4".
 
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finazzoty

Well-Known Member
Gtstorey said:
???
What do your fuel trims show or the narrow band voltage show?
Click to expand...
I do not know for sure if my wideband is setup correctly. I have it tied into the AC pressure sensor. Tune attached for reference (if you have HPT) but here are some screen shots as well:
43708

43709


Also, the second narrowband is not connected as it will not be included in the final setup - going with a straight pipe
 

Attachments

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finazzoty

Well-Known Member
Ross said:
I had a vacuum leak where the DF vacuum line attaches to the brake booster. There is a rubber line that connects from 1/2" tube on the brake booster, down to a 1/4" vacuum line from the intake. I fixed it by torquing down on the hose clamp that has to shrink the hose to 1/4".
Click to expand...
I looked at that as well - does not seem to be a leak there, but I agree, that is a very likely point for one to occur. I've got that clamp cranked.
 
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Gtstorey

Goblin Guru
I'm not sure what the wideband set up has to do with a vacuum leak. But it definitely looks like you are running lean based upon trim/voltage. If it gets better at higher airflow then probably not a vac leak.

I used this with a threaded barb to avoid trying to squeeze a rubber hose down onto a nylon tube. That just seemed like a bad idea.
Brass, Push-to-Connect x MNPT, Male Adapter - 36X057|KQ2H11-36AS - Grainger

I also threaded one into the intake manifold on the other end.
 
Rauq

Rauq

Goblin Guru
According to AEM, an analog output >4.5v is sensor error, so with the AC pressure sensor sitting at 5.0v, the wideband either isn't hooked up correctly, or is reporting leaner than AEM says it's capable of reporting. Narrowband voltage of 0.048v says lean, but that could just as easily be 1.05 lambda or 1.5 lambda. STFT of 32% indicates the engine is trying to add fuel, and LTFT of 0% makes it look like LTFT is turned off.

In short, it looks like you're about where you were in August when I was trying to help. Smoke test it or think about taking the tuning advice you've been given. Otherwise I can't help.
 
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finazzoty

Well-Known Member
Rauq said:
According to AEM, an analog output >4.5v is sensor error, so with the AC pressure sensor sitting at 5.0v, the wideband either isn't hooked up correctly, or is reporting leaner than AEM says it's capable of reporting. Narrowband voltage of 0.048v says lean, but that could just as easily be 1.05 lambda or 1.5 lambda. STFT of 32% indicates the engine is trying to add fuel, and LTFT of 0% makes it look like LTFT is turned off.

In short, it looks like you're about where you were in August when I was trying to help. Smoke test it or think about taking the tuning advice you've been given. Otherwise I can't help.
Click to expand...
Yes sorry @Rauq - Trying to gather some more info before I get back to you in our DM. I actually just sent an email earlier today to Al @ ZZP about why he had LTFT disabled. Quite honestly, I'm probably being over paranoid about making changes, but because I did completely tear down and rebuild this engine (and being its the first time I've ever done this), I'm concerned that I may have done something wrong mechanically and want to rule that out before I change anything in the tune (just based off what Al has told me to do, I'm also worried if I were to change something without him telling me to, he/ZZP would refuse to finish the tune or something).

I did run a smoke test but did not find anything. Will let everyone know what Al says as to why LTFT is off and hopefully this will be the resolution to the problem
 
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Gtstorey

Goblin Guru
I don’t know tuning on your ECM but it isn’t unusual to turn off ltft when tuning. And if tuned correctly long term won’t do much unless something else is going wrong.
It’s real common on the turbo to disconnect the evap solenoid which is the only way to disable the long term and just run on the short term trims.
 
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finazzoty

Well-Known Member
I was wondering if that was the case, which is why I reached out to ZZP/Al about this. This is what I got back from them:
43726


All I can do is chuckle at this point. I guess now I have to wait to get a response from ZZP assigning me a new tuner as the base tune file is still on gate pressure. Sad to see him go.
 
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