Help me diagnose my boost leak issue

blacklab27 · 12-22-2013, 07:40 PM

Installed a jb4 tune and 3" catless downpipes within the past week. Car drove great at first and coming from just a jb+ tune before, the increase in power was really impressive. After doing several hard pulls over the next two days I noticed my car was not pulling as hard at it did at first. By using the jb4 gauge hijacking I noticed my car was maxing out around 11 psi, which was down from the 14-15 psi on map 2 or map 5.

One time while decelerating approaching a stoplight, I had a half engine light appear on my dash and an engine malfunction warning on my idrive system. The began to rev itself between 1000-1500 rpm and power was reduced (guessing it went into limp mode). I immediately pulled the car over and turned it off. Once I turned it back on the car ran fine minus the psi loss. It has not done this again, only one time.

Also when I get in my car to start it after its been sitting for a few hours, my brake pedal is hard as a rock until the car starts and then it goes back to normal.

I'm hoping its just a simple vacuum leak but I haven't been able to find a leak yet. I checked the lines by the oil cooler and everything appears to be okay. I also disconnected the vacuum connector and still get the whoosing sound. I blew into the vacuum line once the connector was disconnected and pressure built up pretty fast and I couldn't hear any leaks.

My car is not throwing any codes besides two for the 02 sensors due to catless downpipes. Can anyone help me out and point me in the right direction to diagnose this problem? Btw my car is an 07 with about 66k miles.

blacklab27 · 12-25-2013, 07:33 PM

Any suggestions? Still haven't found the issue. Going to take it to a shop within the next week if I can't make any progress. I'm a do it yourself kinda person and would love to figure this out on my own.

135Pats · 12-25-2013, 08:15 PM

Quote:

Originally Posted by blacklab27

Any suggestions? Still haven't found the issue. Going to take it to a shop within the next week if I can't make any progress. I'm a do it yourself kinda person and would love to figure this out on my own.

A few things

-The "hard" brake pedal is normal. Has nothing to do with a potential boost leak
-If your car has a serious boost leak, it will likely throw a 30FF code for extended underboost.

So i'm not convinced this is a boost leak problem. It's possible you have a hardware issue that is causing boost and timing to be pulled. A log would be extremely helpful here, but if the car isn't running well I can understand your hesitance to go WOT.

Boost leaks come in all shapes and sizes. I had the cold side intercooler coupler blow clear off and the car wouldn't make more than about .5 pounds. The boost delta you are referencing sounds more like a leaky or dry-rotted vac line, rather than a coupler that has come loose. Check boost solenoids, the vac canisters, and the vac lines going to the wastegates.

blacklab27 · 12-25-2013, 08:44 PM

Being busy with the holiday season and work, I haven't really been able to give the car a good run through. I ordered the usb cable for the jb4 so I can do some data logging and send them to Terry and get his opinion. Thanks for the advice, I will give those areas a good look and report back.

12-22-2013, 07:40 PM	#1
blacklab27 Private 6 Rep 71 Posts Drives: 2008 TiAg e92 335i Join Date: Sep 2012 Location: Raleigh, NC iTrader: (0)	Help me diagnose my boost leak issue Installed a jb4 tune and 3" catless downpipes within the past week. Car drove great at first and coming from just a jb+ tune before, the increase in power was really impressive. After doing several hard pulls over the next two days I noticed my car was not pulling as hard at it did at first. By using the jb4 gauge hijacking I noticed my car was maxing out around 11 psi, which was down from the 14-15 psi on map 2 or map 5. One time while decelerating approaching a stoplight, I had a half engine light appear on my dash and an engine malfunction warning on my idrive system. The began to rev itself between 1000-1500 rpm and power was reduced (guessing it went into limp mode). I immediately pulled the car over and turned it off. Once I turned it back on the car ran fine minus the psi loss. It has not done this again, only one time. Also when I get in my car to start it after its been sitting for a few hours, my brake pedal is hard as a rock until the car starts and then it goes back to normal. I'm hoping its just a simple vacuum leak but I haven't been able to find a leak yet. I checked the lines by the oil cooler and everything appears to be okay. I also disconnected the vacuum connector and still get the whoosing sound. I blew into the vacuum line once the connector was disconnected and pressure built up pretty fast and I couldn't hear any leaks. My car is not throwing any codes besides two for the 02 sensors due to catless downpipes. Can anyone help me out and point me in the right direction to diagnose this problem? Btw my car is an 07 with about 66k miles.
	Appreciate 0 Tweet Quote

12-25-2013, 07:33 PM	#2
blacklab27 Private 6 Rep 71 Posts Drives: 2008 TiAg e92 335i Join Date: Sep 2012 Location: Raleigh, NC iTrader: (0)	Any suggestions? Still haven't found the issue. Going to take it to a shop within the next week if I can't make any progress. I'm a do it yourself kinda person and would love to figure this out on my own.
	Appreciate 0 Quote

12-25-2013, 08:44 PM	#4
blacklab27 Private 6 Rep 71 Posts Drives: 2008 TiAg e92 335i Join Date: Sep 2012 Location: Raleigh, NC iTrader: (0)	Being busy with the holiday season and work, I haven't really been able to give the car a good run through. I ordered the usb cable for the jb4 so I can do some data logging and send them to Terry and get his opinion. Thanks for the advice, I will give those areas a good look and report back.
	Appreciate 0 Quote