Needa little help plz... The rust on my Y pipe flanges intensitied to leak and trigger P0430 code. I ordered the Davico Y pipe from RockAuto after checking with a few folks here with good fitment result. Since I don't have relevant floor to lift 4 wheels off the ground, I had it installed by a muffle shop. Things seem well on the 2.5hr repair except the exhaust is now rather loud. What should I check on it? Being with the quiet sedan for some time, exhaust noise is super annoying now. Thx..

I cleared the CEL with my TS and it doesn't come back after 15mins of driving so far. So, the flange leak should be fixed and the cat sides should still hold air.

 

Out for a drive without traffic, some additional and weird data is collected. 2 observations. 1.) On steady 100km/hr (62mph), it gets 7.1L/100km (33mpg). The car used to get only 8.5L/100km (27.6mpg) at that speed. 2.) The car feels sluggish. Although I can still get the traction control to kick in at light, I don't have the same acceleration response. During acceleration, the current fuel consumption is 20% higher than before.

Anyone has ideas why the car behaves this in addition to the strong exhaust noise after the Y pipe replacement? Thx.

Took a few pics. after the drive, can't see obvious connection issue.


The pinion seal leak was repaired already. That's they the pipe looks oily and dark.

 

My guess and opinion on the change in exhaust sound is that it's due to the aftermarket catalytic converter at the end of the Y pipe. The Davico catalytic converter is smaller and of a different shape than the OEM one. With a background in street racing, I can tell you for sure that catalytic converters can play a large part in how an exhaust system sounds.

The change in performance could be from a lot of things. One possibility is the different style catalytic converter, or it could be the different shape of the bends in the new exhaust pipes. The Davico has what's referred to as "crush bends" or "press bends" where the pipe is placed against a curved jig and pushed on one side to bend around the jig to achieve the required angle. This leaves the part of the pipe slightly crushed inward, changing the diameter of the pipe in that area. I believe all of the factory exhaust has mandrel bends, where a die is inserted into the pipe to help retain the size of the pipe, then the pipe is placed into a jig that encloses around the pipe which ensures that the outside of the pipe does not deform either. Then it is pulled into the desired angle, leaving a uniform inner and outer diameter through the curve of the pipe. There's less chance of it being the crush bends than it being due to the different style catalytic converter, at least in my opinion, but both can have a measurable impact.

Or you could have a leak. The best way to check for a leak is to plug one of your exhaust tips and attach a shop vac in reverse to the other one. With the shop vac bowing air up into the exhaust, crawl under the car and spray all of the connections, joints and welds with very soapy water. Any leak will cause bubbles from the air being forced into the exhaust system from the shop vac. You want to do this with the exhaust cold or else the soapy water will immediately evaporate when it hits the exhaust pipe. You'll want to absolutely soak the exhaust pipe to ensure you're getting soapy water on all sides and in all crevices of the joints and connections. Last time I did this I used an empty Windex bottle and had to refill it three times before I had sprayed all of the parts I needed to look at. Also, spray parts before and after the new pipe to look for leaks there too because sometimes when wrenching on one part of the exhaust it's possible to cause a gasket to separate in another part, especially if things are rusted and violence is used.

 

Thanks walking me through the aftermarket part nature. I should have learned about the parts and brands than just picking the cheapest option from Rockauto.... With my car losing most of the low end torque, I feel like driving with half of the cylinders only. Really undesirable. Unfortunately, I don't have room for a soapy water shop vac leak test at the moment. May I know what type of leak (how large) could cause the lose of engine torque? So, I can explore alternative or potentially back to the muffler shop.... Cuz when the original Y pipe flange leak to trigger CEL, the car sounded and drove exactly the same as if there is no leak. No noise, no power lost.

 

Another thing you can do is make absolutely sure that the noise you're hearing is coming from the exhaust tips and not from some other middle part of the exhaust. If the sound comes from the middle that can indicate a leak. It doesn't have to be a big leak to cause a problem, but I don't think that's your issue if you feel like the car has lost half its low end power. I don't think a leak could have that big of an effect on power like you're describing. I have a very audible leak now and the engine performs just fine. It sounds like an old Chevy van when it starts up. I'll get around to fixing it... but not in this heat.

My other suggestion will hurt to hear. Were it me in your shoes, I'd ask the muffler shop to cut off the Davico catalytic converter and put the original one back in its place and see how performance is then. Other than that, I don't have any other ideas besides using a different Y pipe all together. Doing DIY tests with exhaust parts is difficult because it mostly involves removing parts and testing engine performance without them, which can be very loud and you can end up with more exhaust leaks if you don't reassemble things correctly afterwards. Maybe someone else will have more exhaust experience with these cars.

 

Reading your post leads me to one more problem solving question. The only thing the muffler shop did aside the Y pipe was to uninstall and reinstall the two downstream O2 sensors. IF the sensors were damaged, will it cause engine power lost? After I clear the original Y pipe P0430, no more CEL at the time. Any where I could look at the O2 sensors before messing with the exhaust?

 

Only the front/upstream O2 sensors are important regarding engine performance. The downstream ones only tell if the catalytic converter is doing a good job or not. Even if there is a check engine light and a code for the downstream O2 sensors the car will still run fine. Also this car seems to be very picky about the information it gets from O2 sensors and if an O2 sensor was damaged it would let you know with a light and a code.

 

Something else I thought of on the topic of missing torque at low RPMs... that's usually what happens when you increase the flow rate of an exhaust on an engine that was designed to operate with more exhaust backpressure. It will increase high RPM horsepower but decrease low end and mid range torque. So perhaps the new cat, being smaller and round, isn't creating enough backpressure for the engine to develop proper low end torque. I would be curious to see how the engine performs at high RPMs at wide open throttle - but don't try it out on my account.

 

Nothing gain in higher RPM after a few attempts to floor it on the light. Weirdly, with normal mode, the tranny decided to shift in 5k rpm. Switched to the sport mode, it upshifted in 6k rpm. Without the low end torque, it feels slow on streets. Maybe it's different on a track but....

Got an appointment for the exhaust leak tmr. morning. I think some level of leak is very likely. But no high hope about the engine performance from some minor exhaust leak but to fix the noisy notes at least. Hopefully.

 

You're choking the car's exhaust gasses down, making them more turbulent, read up on the venturi effect. That cat is not big enough on top of being crush bends as well.
https://www.google.com/search?q=vent...ie=UTF-8&ebo=0

 

Oh.... I had checked via internet on a few folks who claimed a positive result from this Davico Y pipe before ordering it. Yet, the discussion had focused on the direct fitment and quietness but not the flow performance.

 

With the car on lift, a small leak is found between the end of Y pipe connection. Thought, a new gasket is used. I now understand why some folks silicone weld or just weld that section all together. Anyways. My two concerns remain: 1. Leaky exhaust noise. 2. Lost of engine torque / power. From the discussion here and validation from the car, it's likely the Davico cat is way too small. My options are:

A.) Cut the Davico cat and weld a straight pipe all together. Question: what will be the consequences to weld the Y pipe to the mid muffler? Will eliminating the cat with a straight pipe be very noisy?
B.) Cut and weld the original Lexus cat back to the car with the Davico Y.
C.) Silicone glues the end of Y pipe on above options instead of cut and weld.

Anyone has experienced these options?


Minor leaks in this joint

Adding further complication, I am likely to deal with a out-of-province vehicle inspection. Unsure if they can tell if the 3rd cat is deleted as the car has two cats already. Yet, the current minor leak may also stop them passing my inspection... Appreciate and welcome on shared
thoughts. Thx. v. much.

 

In my experience, cutting out the 3rd cat will likely make the exhaust louder. Maybe not a lot louder, or maybe enough to be annoying in a car that's supposed to be very quiet. I don't have inspections where I live so I don't know much about how those things go. My vote is with putting the original Lexus 3rd cat back in place though as that will satisfy any inspection and will not cause problems with noise.

In the past I've used Copper RTV silicone on exhaust gaskets, but it works best where two flanges meet with a gasket in the middle. The pipe you show with a leak is what you called a slip fit, where one piece goes over another. Those are prone to leaking and I haven't had much luck using RTV silicone on those. Also, in your picture, it looks odd, like the factory pipe goes over the new pipe, but has a sleeve or something in between. I don't know of that should be there? That doesn't look like a proper mating of two pipes to me. Just my two cents.

 

That's right. Like you said, I started to worry more on mating new parts to old parts. Luckily I got my old factory Y pipe from the muffler shop this morning. Not so lucky as the factory cat is also pretty rusty. Unsure how it will hold up after cut and weld……

 

That doesn't look too horrible, no crusty crumbly chunks of rust anywhere. That end bit in the picture will probably mate up to the original part after the Y pipe better than what's on there now, just have them cut and weld the other end onto the new Y pipe. They can grind the rust off to get a good weld. Also, after looking at your 3rd cat... I think mine may have been tampered with.