Checking the general health of your engine and tune.

Regular maintenance is the key to longevity of your forced induction engine. A major cause of stress to all turbo charged engines, especially MAF based systems are vacuum and boost leaks. As a turbocharger feeds air into a leaking system it begins to spin faster in an attempt to maintain the targeted boost level. This over spin creates decreased compressor efficiency and excess heat. Added heat increases the chances for knock and decreases power. In addition to hotter combustion the location of the leak will greatly effect the air to fuel ratio.

Most vacuum leaks originating between the MAF sensor and turbo inlet will lean out the mixture, as outside are is drawn into the system beyond the point of metering. While boost leaks after the turbocharger typically make a rich in boost as air leaks out. Boost and vacuum leaks can occur in the manifold or tgv area which generate lean fueling in low load (vacuum) and rich fueling when above atmospheric pressure. Leaks will also effect the ecu's function as it tries to trim fuel to meet demands based on its sensor feedback. Learned fuel trims will often be greater than +/- 8. The key to optimal performance and reliability is to regularly check for boost and vacuum leaks. This test can be very simple and accomplished without many tools or a compressor.

Leak Test:

You will need, a flat head screw driver and a plug for the intake 2.75” OD (aerosol can, spray paint etc will work). You remove your intake from your inlet tube, then insert the can into the coupler just in front of the inlet tube. Next you remove the vacuum source line from the by-pass or blow-off valve and blow into the source line (which connects to the manifold). Try not use above 5 psi because the inlet, pcv, and valve breathers will be under pressure and could pop off or generate a leak. The breathers normally do not see boost pressure. I typically blow into the line with my mouth (lungs) because its quiet and easier to hear air coming out of the system. Once all leaks are contained I blow into it and put my thumb over the hose for 3-4 seconds, then release my finger, and it should still contain some pressure and you can hear it hiss back out at you. A smoke test is another good way to locate leak sources but a smoke machine is needed.

Once all the leaks are sorted out its time to check the health of the tune. You will want to reset the ecu and warm the car up. You may now log idle and highway cruising. Observe the “A/F correction #1” and A/F learning #1” the total of these two should be less then 7%. Observe the DAM (dynamic advance multiplier) it should always be at 1.0 on a TA tune. Factory tune starts off at 0.5 and should rise up to 1.0. Email the results to your tuner! If this all looks good your now ready to do a full throttle log in 3rd or 4th gear. It is best to log a single run through part of the power band roughly (2500-5000rpm). No good reason to do multiple logs of the same conditions, especially if something is wrong. Your tuner may give you specific instructions of what to log depending the need. Email the tuner the results. Wait until they confirm is everything is correct. Typically, after the partial pull looks positive you will be asked for a full pull to redline. Followed by short pulls in higher gears. Driver must use judgment and drive responsibly in a safe place, while obeying speed limits laws, etc.

Tuning Checklist:

• Eliminate all vacuum and boost leaks(leak or smoke test).
  
• Reset ECU and warm up engine to operating temperature.
  
• Record a short log idle and cruising. Email to tuner.
  
• Verify DAM = 1 (or 16 on older wrx ecu's)
  
• Record 2500-5000 full throttle in a middle gear (3rd for 5spd/5eat, 4th for 6spd) and email to tuner.
  
• If full boost logs look positive you may drive normally (boosting once in awhile is okay) for a few days. Then record another idle, cruise, and WOT log and email to your tuner. This is to track the long term learning as learned values can be carried across the entire RPM band and can lean or richen the fuel mixture. This can also be done periodically to check up on health, and detect developing leaks.
  

Nice post.

Thanks,

Here is some info on logging parameters (moved attachment to first post). Some parameters vary a bit in newer models so I will try cover them soon.

Check your cars for leaks!

Yep. I am planning to get/diy a boost leak tester and check for leaks maybe once a month, along with pulling an LV twice a month maybe.

Yep. I am planning to get/diy a boost leak tester and check for leaks maybe once a month, along with pulling an LV twice a month maybe.

You not need a boost leak tester, just a can or something 2.75" diameter to plug the intake. Read above.

You not need a boost leak tester, just a can or something 2.75" diameter to plug the intake. Read above.

Yeah. A couple of hours after I made this post, I realized you described how to check for leaks without 'fancy tools' in your OP. oops

Yeah. A couple of hours after I made this post, I realized you described how to do it yourself in your OP. oops

No worries, just trying to save you guys a few bucks.

Any additional advice on how to do this quick and easy boost leak test on a 5th gen? Since the turbo is down low under the engine, the BPV lines don't look easy to get to.

Post a pic of the engine bay with covers removed, and ill see if I can help.

I've got to say, thanks to you and your method I found my vacuum leaks. Pinched intake manifold to TGV gasket and a vacuum hose from the inlet to purge solenoid #1, that was in good condition, but would leak around the connection at idle. It was fast, easy, and I had great results. Once again thank you.

As for the plug to the air box hose, I found that the 2" plastic pvc pipe cap works great. It's OD is 2.75" - almost right on the nose - and the beveled edge end goes into the intake perfectly making a positive seal. It also perfectly fits into the stock throttle body hose, if you need to isolate everything downstream from the throttle body.

http://i.ebayimg.com/00/s/NDI0WDYwMA==/z/eCAAAOxyNa9SKSHq/$T2eC16J,!wsE9suw)yU6BSKSHqW3L!~~60_35.JPG?set_id=880000500F

As for the plug to the air box hose, I found that the 2" plastic pvc pipe cap works great. It's OD is 2.75" - almost right on the nose - and the beveled edge end goes into the intake perfectly making a positive seal. It also perfectly fits into the stock throttle body hose, if you need to isolate everything downstream from the throttle body.

 

http://i.ebayimg.com/00/s/NDI0WDYwMA==/z/eCAAAOxyNa9SKSHq/$T2eC16J,!wsE9suw)yU6BSKSHqW3L!~~60_35.JPG?set_id=880000500F

I used the cap from my pbblaster can. Works perfectly

I've got to say, thanks to you and your method I found my vacuum leaks. Pinched intake manifold to TGV gasket and a vacuum hose from the inlet to purge solenoid #1, that was in good condition, but would leak around the connection at idle. It was fast, easy, and I had great results. Once again thank you.

 

As for the plug to the air box hose, I found that the 2" plastic pvc pipe cap works great. It's OD is 2.75" - almost right on the nose - and the beveled edge end goes into the intake perfectly making a positive seal. It also perfectly fits into the stock throttle body hose, if you need to isolate everything downstream from the throttle body.

 

http://i.ebayimg.com/00/s/NDI0WDYwMA==/z/eCAAAOxyNa9SKSHq/$T2eC16J,!wsE9suw)yU6BSKSHqW3L!~~60_35.JPG?set_id=880000500F

Awesome! This is why I wanted to post this.

Leaks kill engines

Leaks kill engines

SO true.

Thanks for this checklist, Mike.

The standard design has always bothered me.

Could you elaborate?

Could you elaborate?

-Ability to seal at various boost pressure

-Reaction time (They're too slow to respond)

-Pressure differential (requires a greater pressure differential than the spring pressure to open the valve)

Bump for a good thread, but also have a question or comment...

I believe I am having some fitment issues between my avo intercooler and stock throttle body hose. I swear, it's probably been the 20th time I am taking that stuff apart and putting back together to fix a boost leak. Each time I do this and reset the ecu, trims are good. 30 or so miles later, they slowly creep back to -10 to -15%, especially the first and third trims (and eventually the other two).

I then do a leak test as prescribed in the OP, and can't hear any leak. Even after waiting for 10 sec, air rushes back through the bpv hose .

What would you guys suggest at this point? I am at a loss and really frustrated. I may as well just go ahead and buy an AVO TB hose..

Target boost is 18.5 or so psi btw.

It could be a normal part of the relearn of fuel trims for the pcm, however, I am not a tuner, just a good mechanic.

How many miles are you driving between pulling the avo hose off an on?

Yes it burned oil. The misfire on #4 was constant at idle, not enough for a check engine light. Under load it felt a little sluggish, no misfires.

The misfire prompted the compression test and leak down test.