supersnake67

Just need a little info, installed my pypes x pipe on my 2004 GT and installed new pass. side gasket with graphite ring facing the manifold and instantly got a lean code on that side for the down stream 02 . Did a little swapping of parts side to side to see if I could isolate it and the same code comes back so it has to be an exhaust leak on pass side flange . I did some research and some say gasket should face manifold and others say should face x pipe ??? Which way is right? I'm tired of taking the stupid pipe off to try and diag . The pypes x pipe has a little recess along the top and it's flat on the bottom. The factory mid pipe has a full recess around the whole flange .So either I mangled the gasket on the install or have it on wrong ? Just trying to fix my CEL

cliffyk

The ring should face the pipe, so it seats in the flare...

supersnake67

The x pipe right ?

cliffyk

I take that back actually, it depends on what the flange on your X-pipe looks like--can you get a photo?

supersnake67

No I dont ave a pic cause the pipe is on the car but it has a small recess around the top and is flush with the flange on the bottom . Called pypes to make sure it was right and they said yes it's suppose to be like that . I just dont want to keep buying gaskets if I'm putting them on wrong

cliffyk

From what you describe the flat side of the gasket should be against the flange on the X-pipe...

supersnake67

Thats what I thought, cause the manifold has a deep recess so thats how I originaly put it in . When I pulled the new gasket off it was blown out around the spot welds , why i'm not sure. So if I had the gasket on right and tight I could see maybe having an exhaust tick from leaking but how would it be that bad to cause a lean code?

cliffyk

If the flat side of the gasket does not seat well on the pipe's flange you might have to file or grind down the "flush" part you referred to.

The exhaust flow, like the intake flow, is not a steady stream of gas; but rather a series of sort of tear-drop shaped pulses of gas, each with a higher than ambient pressure head, a close to ambient pressure body, and a less than ambient pressure (vacuum) tail¹.

When the head, at higher than ambient pressure, passes the leak it pushes gas out through the leak making no change to the gas' O2 content. When the body passes, at ambient pressure, nothing happens again making no change in the gas' content.

However when the pulse's tail, at less than ambient pressure, passes the leak it sucks in air making the O2 sensor read it as lean. The mix really isn't lean, but the O2 sensor tells the PCM ii is. The PCM will then recalculate the short term fuel trim, adding fuel to correct the "lean" condition--when the STFT reaches +25% and the O2 sensor still says it's lean the code is thrown...


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¹ - The intake pulses (n/a) are the opposite of this, vacuum in front, amibient in the middle, and higher than ambient at the tail.

supersnake67

Great explanation makes more sense to me now. Thank you I tried to feel and listen to the pass. side and did hear a tick that echoes all over but is more prominent up front. The passenger side is so tight its impossible to feel for air leaking around the flange or really tell if the flange and gasket mount up square with each other. So does the gasket mount with the ring towards the factory mid pipe when stock ? And if so I wonder why pypes doesnt put a recess in the down tube. Any special tips for putting the x pipe on ? The last 3 times I used a screw jack under the crossover let the gasket hang on the studs slid the downtube onto the studs tightened the pass. side bolts, put the driver side down tube on and tightened them then moved down on the driver side where the ball and socket bolts before the crossover and then finally tightened the cat back up. Dont know if you see anything in my install where i might be wrong but if you do please let me know . I really appreciate you taking the time with me on some of these other sites i'm lucky to get a ''HUH'' or buy a tuner . So just wanted to say thanks

cliffyk

You are welcome, I am too old to play school-boy head games.

The process you describe is correct, as the passenger side is a fixed angle solid connection it should be clamped down first. Then the adjustable angle ball-joint on the driver's side.

Make sure the gasket on the passenger side is lying flat on the pipe's flange, and that it stays aligned as you clamp it down (or I guess "up" since you're under the car).

Did the pipe come with a short stub, with a socket joint, that fit's inside of the driver's side pipe? If so use it as it makes the 2-1/2" socket on the after market pipe seal better on the stock "ball" on the manifold.

Sort of a kludgy thing I have done when assembling flat flanged exhaust connections is to use a thin coat of muffler cement on both sides of the gasket and the flanges. That stuff will not actually repair mufflers as is claimed, however it can provide an extra edge ot sealing on flanged connections.