not building boost, am i missing something? Options

[easternpiro1]

Hi all, was wondering if i can get some feedback on something i was missing. here's the story:

recently a friend and I fixed a leak due to stripped thread in the head causing a leak between the exhaust manifold and block.

after rethreading and putting everything back togehter leak is gone BUT now im seeing much lower boost numbers after taking it for a drive.

I own an AEM tru boost controler/gauge and the boost is currently set to stock wastegate pressure (8psi) and consistently held this pressure PRIOR to fixing the exhaust leak.

as of today, my first drive out, my car would not pull past 5psi and touched 6psi BRIEFLY. I double checked my IC piping and adjusted and retightened.

when i went back out the car would only boost up to 4-5 psi adn sometimes as low as 2-3 max.



Im pretty sure its a leak somewhere but it can only be one place as the only IC piping that was removed was the piping coming from the turbo (charge side) i have checked and double checked it.

is there something im missing? any helpful hints would be appreciated! thanks!

[easternpiro1]

before switching the turbos I decided to test the turbo by "dead heading" it and inserting a pressure gauge measuring in PSI. some say the turbo needs to have load on it however even standing still should it not be blowing out more pressure?

turbo test

Matt, the thing about this test is that there is no load on the engine. You are really not supposed to be able to build any boost this way. I bet I would get exactly the same results if I did this on my car and my turbo works fine.

I figured as much and i knew better! lol did it anyway to make sure. I remember when sitting still on my previous swap, i could rev the engine and there would be Blow off. It no longer does it.

Lagos is right on this one. The test you've done is useless. At free-revving, there isn't enough exhaust air flow to drive the turbine at a high enough RPM to build boost on the compressor side. Also, a turbo isn't a positive displacement pump. Unlike a roots supercharger where there is always the same volume of air forced into the supercharger, it's not because a compressor is doing a revolution that a certain amount of air will be force into the compressor outlet. It takes a lot of turbo RPM to build boost o the compressor outlet side.

I can't beleive you have not ruled out this problem yet. I'm not saying that you didn't try hard enough, you certainly did. But I'm sure you missed something really basic. A turbocharger isn't something that is really complicated. I suggest you to go back to the base. Do a boost pressure test from the turbo compressor. Be sure to block off the IAC inlet. Verify that you can get at least 30 PSI in this test.

The other test is to verify that the wastegate stay shut and that all the exhaust airflow actually pass through the turbine.

Then, physically verify that turning the turbine result into a compressor revolution and make sure that the shaft is turning freely. Verify that the turbine wheel is in OK shape (no bent/broken blades).

If all those points are ruled out, there is no physical reason for this turbo to not boost.

Are you sure your boost gauge is accurate and correctly connected to the intake manifold. It should read about -19 inHG at idle, 0 psi when the engine is off. Verify if it is correctly displaying a boost event using a mityvac or compressed air (be sure to use a pressure regulator and set it at around 25 PSI).

Do not give up!

Sam

thanks for the vote of confidence sam! I have done almost everything at least twice.

I will do another boost pressure test as last time I didnt run it THROUGH the turbo compressor I took the piping off of the turbo and pressurized from beginning of piping to end. (I was told I would ruin the turbo if too much PSI was put through it)

I took the turbo off (even separating it from the manifold) and spun it while inspecting all areas smoothly without touching the housing. all looks good on the fins as well

boost gauge reads 0 when car is off however when at idle it fluctuates from -14HG to -16 and has gotten as low as -12 at times.

as far as the IAC is concerned, I do notice that the car will idle strangely (drop in RPM from 1000 to 800, and at times feels like it wants to cut off) After fixing a hole in the hose nest to the IAC there is still some trouble, but I will clean the IAC with brake cleaner to be sure.

Im fairly certain that the WG is closed and that the flapper is ok as I have placed the car on a dyno without downpipe to inspect it and hold it closed

wastegate/dyno


again thanks for all your help guys! I will keep trying!

This post has been edited by easternpiro1: Feb 15, 2013 - 7:14 PM