20 idle Vacuum but BLT only 5psi

[BostonGST]

My idle has always been perfect and my boost gauge reads about 20 vacuum. I did a BLT today at a gas station and it only went to 5psi. Really hard to do off a busy street trying to hear leaks, i think i may have heard something near the TB. I tried spraying soapy water and saw no bubbles coming up. idle vacuum is 20 and car boosts to 10psi (has a 16g with stock WG).

Is there definitely a boost leak? Or am I doing it wrong? Hook up to turbo inlet, removed oil cap, seems pretty straight forward..

 

[2gGst98]

Sounds like you are doing it right. Maybe you hit the unlucky part and had some over lap on one of the cylinders. If so just bump the engine over once and try again. Do you hear it from the exhaust at all? If so you probably got overlap. When you try agin listen for leaking in the exhaust mani. I know how it is trying to do it near a busy road. I spent about 45 min trying to find all my leaks when I did it at the gas station. Hope this helps

 

[PlanZero]

I've never removed the oil cap when doing a BLT. TB shaft seals are probably leaking a little. They all do at this point if they were never replaced. Not enough to drop 5psi though.

 

[pauleyman]

Id question the method more than results. Find an air compressor and test again.

 

[Mauispyder]

If the TB seals leak at 10 then you'll lose 5psi. My blt didn't bubble either until I got the spray way under the tps, even then it was only one big bubble than no more. Bigger leaks in cluttered spaces are harder to detect with bubbles. The leaks tend to blow out the soapy water too fast to make new bubbles especially if gravity is against you.
Btw vacuum leaks (loss of vacuum) almost never correlate to boost leaks. This has to do with the shape and flexibility of tubes and seals acting essential like a one way valve.

 

[4g63dailydriver]

I am having the same problem. Although I found a leak at the boost gauge due to the crap nylon line. And the idle screw adjuster on the throttle body...having trouble loading the rest of the pictures...

 

[miguelmcv]

An air compressor is the best to have when doing a boost leak.

If you have a hard time to find a leaks then do it in stages,,.
Do a boost leak from the throttle body and you will be able to hear/find what ever leak you have in the intake side,.
Then do on other leak test at the end of the turbo (turbo outlet) and finally you can do another from the turbo I let.

Remember, some turbos will leak in to the motor when not spinning so you will loose some air in that area.

 

[GST Jeremy]

I built my BLT from the local hardware store and started going crazy finding all the leaks. find someone that has a larger compressor, away from a busy highway, then you can charge your system without having the compressor running. makes it much easier to hear the air pissing out. my car would only hold 4psi when I started. the major leaks were at the injector seals, 16 bucks and any auto parts store, and my TB shaft seals. my tb seals were so bad it would not hold over 6 psi after I changed my injector seals. now I can blt and hold around 25psi. still has a couple small leaks at the tb but doesn't really affect it

 

[GST Jeremy]

I am having the same problem. Although I found a leak at the boost gauge due to the crap nylon line. And the idle screw adjuster on the throttle body...having trouble loading the rest of the pictures...

You can order a BISS screw and o ring for like 10 bucks or less and eliminate that problem area anyways

 

[4g63dailydriver]

You can order a BISS screw and o ring for like 10 bucks or less and eliminate that problem area anyways

Where do I get it?...my local part store did not have it...

 

[4g63dailydriver]

this is the BLT detector I put together...under 15 bucks...

 

[Chumpaumpalumpa]

Where do I get it?...my local part store did not have it...

Have your pick

http://www.jnztuning.com/product_info.php?name=BISS Screw (DSM)&products_id=1301

https://www.extremepsi.com/store/product.php?productid=19022

 

[GST Jeremy]

Where do I get it?...my local part store did not have it...

I have had really good luck with STM. ive gotten a lot of misc parts from them. Great customer service and fast shipping. I have used extremepsi they are good as well

 

[Chumpaumpalumpa]

STM is great but they tend to be the most expensive which is why I did not list them here.

 

[Mauispyder]

I was in a hurry and got my biss o ring from ace hardware, just took the old one with me, and got a little dielectric grease as well to put on the o ring. Don't forget to screw the biss in to the exact same level as it was at. Screw it all the way in, counting the numbers of turns it takes. Unscrew it all the way and replace o ring (you may need to pressurize the TB to get that biss to pop out). Screw it all the way in and unscrew the same number of turns you previously counted when you screwed it in all the way.