2G Turbo and O2 housing Gasket Leaks

[tgounev]

The symptoms: The car would spool slow and can’t reach the max boost. Used to max at 24-25 psi – now it goes to 19-20 psi. You can hear a whoosh sound during boost – like something is deflating. The A/F gauges show lean condition during idle, which forces the LTFT to keep adding fuel, but the A/F ratio is fine during cruise and WOT.

What I did: First, I did a boost leak test and found leaks in the throttle body. I sent the TB to be refurbished (shaft seals, etc.) and when it came back, the intake leaks were gone. The BLT held good until 22 psi where the BOV starts to leak (I think that’s normal for 1G BOV, please correct me). Second, realizing that I must have an exhaust leak, I tested it with a shop-vac in the exhaust pipe and soap water. I had leaks on the exhaust manifold gasket and the turbo and O2 housing gaskets. I replaced all 3 gaskets. Had to put a helicoil in one of the manifold stud holes as it was stripped, which caused the leak on the manifold gasket, then used a Fel-Pro gasket for the manifold. Got the other 2 gaskets from ebay. They looked thinly made out of one layer steel. Put everything back and torqued the turbo and O2 bolts to 42 ftlb. Went for a test drive – same problem (maybe even slightly worse). I tested the exhaust side for leaks again. No leaks on the manifold gasket, but the turbo and O2 housing gaskets were leaking just as bad as before.

I am out of ideas. It has to be the exhaust leak. Would such a leak cause a 5 psi drop in boost and very lean idle? If it’s the gaskets, are there any more “forgiving”, thicker and softer gaskets I can use on the turbo-to-manifold and turbo-to-O2 surfaces? Thanks.

 

[bratte88]

I did all the sanding, etc., and there are no external leaks at the turbo and O2. The cracks are on the inside of the turbo housing at the wastegate hole, so I would have to replace the turbo housing. I would kick myself if I replace it, and later find that the BOV is leaking my boost, not these cracks. I'll have to buy a BOV to find out for sure, but I was thinking of "crushing" the old BOV first to see if strengthening the spring would give me more boost. Why do BOV's leak? Is it just the spring getting weaker over time, or there could be other reasons for poor sealing?

crack is a crack, I woudlnt want to use a turbo with one.

BOV leaks because of a number of reasons, gaskets, build qualtity, overboosting

 

[tgounev]

Guys, I know that you are most likely right and the cracks around the wastegate are the reason for the loss of boost and poor spool. But trying to avoid dealing with the big problem hoping for easier solutions is just "human nature" . I crushed the BOV, but no change. There are a few more things I want to do before dealing with the cracks (replacing bad ISC and block-off EGR valve). I remember in the winter I had forgotten unpugged the harness of the EVAP (or EGR) solenoids when all these issues began and I could not get much boost at all, so I am obligated to check the EGR.

I am thinking of a crazy option and I need your opinion. What if I weld the wastegate flap all around including the cracks above and below it. I don't remember the last time I touched my boost controller (it's maxed out), so I am running at the upper limit of the turbo and I don't care for lowering my boost. Would deleting the wastegate (and not having external one) present any other overloading issues with the turbo?

 

[tgounev]

The boost issue has been RESOLVED! No, it wasn't the cracks around the wastegate hole. It was a collapsed catalytic converter! The way I came up with this is, I tied up the wastegate shut with a wire and did a few WOT runs. I was able to get higher boost generated at high RPMs, but the power was low and the car was knocking. I concluded that this was due to back pressure in the exhaust. If the wastegate is not tied up shut, the high back-pressure in the manifold pushes the flapper open, so the gases go around the turbine wheel, and the boost can't get higher. So Checked the cat and it was blocked by chunks of catalyst rolling around. I gutted the catalytic converter. All the loose stuff came out and the cat is just an empty pipe now. The boost spikes to 28 psi now, so I had to lower it with the boost controller!

But my problems didn't end here. With the gutted catalytic converter, something changed in the tune of the car, and now it's bucking at around 5000-6000 RPM. There is no knock and it sounds like a fuel issue. Is there a known issue that occurs after elimination of the catalytic converter? There is a sensor on the exhaust pipe right after the cat (rear O2 sensor maybe?) that's connected to a harness. Could this sensor be giving some bad info to the ECU?