i have a homemade boost leak tester , works great on everyones car but mine... i cant get any more then 2psi while pressure testing , but while driving have no prob holding 25-27psi (the magic # is 33psi). i was told to open the throttle body , i did that and it got me nowhere ... any ideas???

 

I have the same issue with mine and I'm thinking its something with the valves.

-E

 

its driving me f***in crazy....

 

Just a shot in the dark but did you try the test at TDC?

-E

 

are you using the same pump as you were with the other cars? I tried dong mine with a hand pump and it would only get to like 5 psi if I pumped like crazy. Had a shop do it on a compressor and it was nice and tight

 

im using the same air compressor with every car...

 

i guess i'll give that a try, but if you think it is cuz of the valves and i try it at tdc , some vavle somewhere down the line will be open...

 

Worth a shot... I know some gurus recommend doing the test at TDC.

-E

 

are you talking about a "leak down tester" that you screw into the spark plug hole and test the individual cylinders? if so if you have overlap on your cams you will get this.

 

Well with a leak down tester you have to have the piston at TDC on the compression / power stroke. It has to be there for a) the valves to be closed and b) the piston at TDC so the pressure can't push the piston down.

As for a boost leak test, I feel you man. I've boost leaked a few cars and some really don't seem to hold pressure well, even though there is no significant leaks. On mine own car I know my q45 throttle body shaft is leaking a bit, but it doesn't seem like a big one, yet I can't seem to hold much psi in the boost leak. I guess I have a leak somewhere but dunno where. I hold boost fine but assume I'm leaking somewhere.

As for the air going through the valves when overlapped, if you put the motor at TDC, then you definitely WILL have valve overlap on somce cylinders, since TDC between exhaust / intake stroke has overlap. So something like 90 degrees after TDC I think would be ideal.

I've sort of given up on boost leak tests I get annoyed everytime and can't find or fix the leak I have like a TB leak, etc. Does anyone know of something like a smoke I could use where you would see it escaping but wouldn't harm the motor? Maybe dry ice or something

 

He should be talking about a boost leak tester since A. That's the title and B. Not too sure how many people can make a "homemade" leak down tester.

 

i thought that but then i've never seen a boost leak test fail to charge to boost pipework unless there's an obvious major leak or its not been correctly sealed prior to test (maf,bov,throttle plate etc). so thought he must be an about a leak down as that will lose air if not at tdc excatly or using wild cams

 

Try with cams removed

 

true that man!!! im ready to pull my hair out... as far as the "smoke" many automotive tool suppliers cary a smoker used for exahust/intake manifold leaks... the machine burns baby oil and pumps it through the system ( much like on the smoke stack of a steam engine on a old model train) this will not affect the motor, but expect to pay $100-$250 for one check northern tool and supply....

this makes the most sense to me , maybe due to the cams overlap its not allowing compression... as a matter of fact ive never been able to boost leak test it since the install of the 272's...i bet it will work with the cams out thanks

 

Ive tried it both ways and didnt really notice a difference. Depending on how you control boost, it could be a bleed off port?