# Did a boost leak test - now hard brake pedal?



## Aaron16V1.8l (Aug 12, 2007)

Hi all - So I performed a boost leak test this past weekend. I capped the hole in the tip where the outlet of the prv valve goes into to avoid filling the intake with oil, and pressurized the system to 1 bar. I noticed a loud hissing at the passenger side firewall area, and there was a split in the hard plastic line where it mates up to a check valve that goes the brake booster. I suppose this should have been a red flag that some downstream check valve was not doing it's job, as pressure should not show up at that spot? I taped this up and put a hose clamp on it, and that leak stopped. I tested again, and heard/felt a leak around the larger outlet of the suction jet pump under the intake manifold. I couldn't exactly see where the air was coming from in this in this area, as it is really cramped so it could be a different hose in that vicinity. Anyway, I ordered a new suction jet pump and Forge hoses to replace the three hoses that go to the suction jet pump. I will replace all of this this weekend. 

My problem now is that when I go to start the car, the brake pedal is rock solid. Prior to doing the boost leak test I never, ever had this problem. Once the car starts and vacuum is created, the brakes work fine. Obviously there is some faulty check valve somewhere and vacuum bleeds off when the car sits. I am thinking that the sustained boost leak test just pushed some check valve over the edge that was on the border of failing anyway? If the suction jet pump is bad, would that cause me to lose vacuum after sitting and cause the hard pedal? Or is it likely the check valve where I had the split in the line at the firewall? I suppose it is easy enough to check this weekend. Does the brake system only have that check valve near the firewall, and the suction jet serving as check valves? I thought I remember reading there were two check valves in the brake system ... What other spots should I check? As I said before, the pedal never did this prior to the boost leak test. 

Thanks for any help or input, 

Aaron


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## Marcus_Aurelius (Mar 1, 2012)

You likely busted the booster check valve and need a new one, that's what is primarily keeping vacuum stored in the booster. 

The suction jet pump also act as a check valve for the brake assist. One of the two mini diaphragms in the SJP is a one way valve for the booster circuit that allows air to flow in one direction (manifold under vacuum). In order to completely loose brake assist (if the lines are sealing) is to have a failed check valve (by the booster) and a leaking SJP. If one of the two is working properly, you'll be able to store vacuum and have assist. Being that you said that your pedal is rock hard, you must have busted both.


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## Aaron16V1.8l (Aug 12, 2007)

Thanks for the reply!

I pulled the old sjp tonight, and it was completely shot. If I held the small angled port closed with my finger and blew into the large port that goes to the manifold, I could blow through it. So like you said, since the check valve function in the sjp was broken, all the pressure went through the brake vacuum hosing up to the check valve by the booster, and was just too much and did it in. I guess I am lucky I did not ruin my brake booster. Now I have to decide whether it is worth 80.00 to buy a new factor check valve and associated booster hose, or jury rig a new check valve in that hard line. I am leaning towards biting the bullet for the factory assembly.

I did another boost leak test tonight after I replaced the sjp and installed the little forge silicone hoses for it. No leaks are evident in that area now. However, I did however notice a gurgling sound in the oil pan area this time, which I did not hear before. Initially I thought that meant that my PCV valve was probably shot, but reading some other threads suggest that it is pressurized air going past the turbo seals and into the oil feed line for the turbo and back into the oil pan? Whatever the case, when I shut off the pressure to the boost leak tester, it takes several seconds to fall back to zero. I assume if the PCV valve was in fact bad, I would lose pressure much faster...


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## lite1979 (Sep 9, 2005)

$80 for a check valve? If you already got the Suction Jet Pump, then that should be the only expensive one, and you can get them for a lot less than that. Generic check valves are pretty cheap, too. 

If you hear gurgling in your oil pan, don't be alarmed. Your turbo is supposed to have zero shaft play _when oil is coating the shaft_ ideally. A little shaft play when it's dry is absolutely fine. If air is entering the compressor side and making bubbles in your oil pan, odds are that your turbo seals are still good, or you would be burning oil at boost and smoking like crazy. If the air was leaking through the exhaust side of the turbo I would be more concerned.


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## Aaron16V1.8l (Aug 12, 2007)

Thanks for the reply. Good to know the gurgling isn't anything to be alarmed about.

This is the 80.00 check valve:

http://www.partsgeek.com/gbproducts...+Google+Base&gclid=CKquhrvO0MMCFYtr7AodSkcADA

Instead of buying that, I suppose one could splice in another check valve somewhere in that line for the cost of a generic check valve, some silicone tubing, and a few hose clamps. That would accomplish the same thing. 

After having a few too many beers last night and an exciting night working alone on my TT on a Friday evening, I neglected to say that even after installing the new sjp, I was getting a hissing at this elbow of the brake booster hose (you can see my hose clamp and tape job to try and seal it):









That means that the freakin new sjp is bad, the sjp is supposed to bleed boost, or the other check valve under the manifold is bad. In the following pic, you can see how I had replaced a while back the section of hard line with silicon hosing to fix that common boost leak where the line meets the check valve:









I disconnected the hose and applied 15 psi of air pressure to that check valve, and it did not budge. I guess that means my new sjp is crap. I didn't know that there were multiple revisions of the sjp - the one I installed is the earlier revision b, which I bought new off of a foreign car place on ebay. I just placed an order for a Kayser "revision d" one from ECS for 15.00, as I had to order a new rear wheel speed sensor and haldex service kit anyway. Hopefully that will finally fix it. Am I correct in that there should be zero boost leaking past the suction jet pump? 

Thanks -


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