Hey everyone,

First time poster but learned a lot by reading here for some time now. I'm having an issue for a bit that has me pulling my hair out. I have a 2011 MCS with an N18 engine that I bought this past Winter. Recently it threw a CEL for underboost. After some diagnosis I thought that the wastegate was bad. So I decided to upgrade the turbo (might as well go bigger as long as I'm doing this). So I replaced it, cleared all the codes and it was still underboosting.

I tested the wastegate on the new turbo by applying vacuum manually and it worked just fine. I attached a vacuum gauge to the vacuum line from the pressure converter and realized that at startup, the gauge showed -10 inHg in vacuum then died off. But that was it. After startup the vacuum released, the gauge dropped to zero and didn't move under any kind of engine load.

I thought that possibly the pressure converter was bad, or that I had a leak in one of the vacuum lines, so I replaced all the vacuum lines between the pump, tank, pressure converter, and wastegate. While I was at it, I replaced the vacuum tank and pressure converter as well. But I'm still having the same issue. I re-tested with the vacuum gauge with the same result. My only thought is that the problem is somewhere electrical, where the pressure converter is not getting the right signal to apply vacuum and close the wastegate, but I'm not sure. I need help!

 

 

I have read the vacuum pumps can get flakey... doesn’t sound like you tested that yet? If you are sure it’s a vacuum problem, and you replaced all the other vacuum related pieces, might want to look into that next.

 

Thanks for the feedback. I knew it wasn't the vacuum pump because there was the proper amount of vacuum being applied to the wastegate at startup. I figured it out and have gotten it working.

When I first started having issues with the turbo I had replaced a few sensors (Boost and MAP) just to be sure those weren't the issue. I think I got a bad boost sensor though, because I went back in and, just for fun, cleaned up the old sensors and put the originals back in. Lo and behold, the wastegate started functioning properly and I was back to proper boost levels. So for those that might have the same issue, check your sensors.

As a side note, I got about 5 miles having lots of fun with my now-functioning turbocharger and wound up killing an ignition coil. Have that on order now so hopefully that'll be it.

 

*may want to double check your ground connection on the front of the head too.. you start popping coils, and you can corrupt your DME on the ECU. Just make sure ground is 100%.

 

cornjuice Thanks for the reply. Forgive the ignorance here but where is the ground you are referring to? Would like to be sure before I start tugging on wires.

 

I'm having a similar issue... Replaced turbo, diverter , downpipe (I know that isn't the issue) and now I'm assuming its something to do with vacuum.


This was the (old setup)

that exhaust gasket was toast.


The new setup.


All new gaskets, new studs on the turbo itself, turbo gasket replaced as well. Is it possible different vacuum hoses are different psi rating? And I could possibly have the wastegate and that other line crossed? ANY help / insight would be helpful. I didn't want to go and purchase a new vacuum pump and pressure converter without exhausting all other options.


Thanks in advance for any help.

 

When I was having my issues I wanted to rule out any of the vacuum lines and pressure converter so I ended up testing the system by putting a gauge on the line to be sure it was pulling vacuum. I did wind up having a cracked vacuum line though. So I replaced all the lines, reran my test and found that it was getting the proper vacuum, so the pressure converter was fine. Run to Napa and grab a vacuum gauge and pull the line from the waste gate and put the gauge on. Give it a few revs and make sure it's pulling vacuum. If so, you can rule out problems with the lines, pressure converter and vacuum reservoir.

 

Following with interest.
I’m having a minor issue that I have been frustrated with for quite some time now. It’s not the same symptoms as you, my wastegate function is fine. But I think I have narrowed down my issue to either the boost/pressure converter, vacuum tank (unlikely), or the EVAP purge valve.
Anything I can learn along the way may help!