Jump to content
HybridZ

Dropping Boost Pressure


Recommended Posts

My boost pressure keeps getting lower and lower as the engine warms. Also every time I drive the car the peak pressure is a little lower than last time. For example, I made about a 20 mile round trip down the interstate and back. Starting out my boost pressure was about 20 psi on the way back I could only hit 12 psi. I let the car cool for 30 minutes and was able to hit 17 psi. That was October third. On October 10th I took a very short cruise of maybe 5 miles and hit boost three times. First hit about 15 psi, then 12, then could only get 8 psi. This was with no hoses connected to the wastegate. Ther car had been working great until recently running 25 psi. I had the turbo rebuilt in 2011 with maybe 5000 miles put on it since. It's a garrett TC4305 58mm with .82 tubine housing, 3" exhaust dumping about 24" from the turbo. So what I've done so far to diagnose the problem...First I removed the wastegate. It's a turbonetics evolution wastegate. I disassemble it thinking the spring may have been broken. Nope it's fine. I applied regulated air pressure to the bottom port and it cracks open at 15 psi. I also fabricated a tool to see how much back pressure it takes to open the gate. It leaks with only 1psi applied. So I disassebled the gate again and lapped the valve to ensure a good seal and retested. Still leaks with 1psi applied. This does not seem normal to me but I don't see and physical problems with the wastegate as everything appears ok. I also used a smoke machine to check for leaks in the intake, piping, and intercooler and found nothing. Anyone have any input or things I need to check? I will attach my datalogs. Thanks

Link to comment
Share on other sites

I'm not really thinking the turbo is bad. The last time the turbo failed I could hear the compressor wheel scraping the housing. I'm really thinking something is wrong with the waste gate because it doesn't hold pressure on the exhaust inlet side. Odd thing is I don't see any physical problems with it. I think I'll try a test drive with the waste gate blocked off. I'll just have to watch pressure closely.

Link to comment
Share on other sites

Have you tried plumbing the wastegate boost reference to the intake manifold instead?

 

If the boost comes back (maybe even a bit higher because your reference is now after the piping and intercooler pressure drops) and stays back, then you have a leak between the turbo and the intake manifold.

Link to comment
Share on other sites

With no hoses connected to the wastegate it should technically boost until the turbo runs out of breath, probably around 30psi. I want to try utilizing both ports on the wastegate. Keeping some pressure on the top port seemed to help slow the leakage while testing the wg off the car. I'm convinced this wastegate problem is the reason why I don't hit full boost until about 4500 rpm.

Edited by skirkland1980
Link to comment
Share on other sites

  • 2 weeks later...

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...