Exhaust Down Pipe 96 Passat

[dieB4sel]

Recently the timing belt was changed on my car (113k miles)performed by one of our members (very cool to watch). He suggested I also replace the down pipe of the exhaust as it is likely congested.

On my car the down pipe appears to be an integrated unit from the manifold to the "catalyst"... while the Bently manual and the illustration received from IMPEXFAP.COM show it to be a two piece with flang bolt-on configuration.


My questions:
1. Rather than replacing this down-pipe/"catalyst" section, can it be taken off, cleaned out and then reattached?

2. If I must purchase a new down pipe, will the two-piece replacement parts be a straightforward job or is there usually some custom fitting involved? This also includes the funky fact that the 96 Passat had that 5th injector going into the down pipe (I blocked the 5th injector seveal years ago). I am not sure what to do with that injector fuel line... could it just be rolled up and moved out of the way?

3. If there is an option to replace just the down-pipe and have it welded on to the old "catalyst", is that reasonable... or is it likely that if the down-pipe is clogged that the "catalyst" may be constricted as well? With the cost of having that welded on, would I just be better off replacement that "catalyst" with the two-piece?

Thanks for your insights - dieB4sel

 

[RIP TDI]

What was the diagnosis? That the catalyst was plugged, and if so, what were the symptoms? Or that the flex-joint was congested with soot, thereby stiffening it and causing an exhaust resonance?

 

[dieB4sel]

The car does have have a resonance somewhere around 2200-2400 RPM. He tapped the down pipe and thought it was stiff but I don't recall anything done to check on the status of the "catalyst".

 

[RIP TDI]

If the catalytic converter is not plugged, it's core is intact and the flex joint is not cracked/leaking, there is no need to replace the down pipe/cat. The replacement unit is one-piece, expensive and won't solve the exhaust resonance problem in the long run. Neither will cleaning out the flex joint.

If your goal is to get rid of the resonance, the most cost effective way is to install a 2nd flex-joint to the exhaust system, just in front of the center muffler. A more involved solution would be to remove the OEM flex-joint and replace it with one that is 3 or 4 times longer. The results might or might not be an improvement over the 2nd joint installation method.

 

[dieB4sel]

I hear you on the idea that if it isn't clogged...dont try to work on it. I suppose the question now is... what is the best way to determine if it the down pipe/cat is clogged.

 

[RIP TDI]

Here's the procedure for a 2nd flex joint installation.

 

[RIP TDI]

what is the best way to determine if it the down pipe/cat is clogged.

What lead you or your TB installer to conclude that it might be?

It can be phsically tested by installing a pressure gauge in the inlet and outlet temperature probe ports in the cat and checking the pressure differential, but a plugged cat would show up in the car's performance...low boost pressure and fuel mileage with all other causes eliminated, e.g.

 

[dieB4sel]

Thanks Chris for your great input!
My typical milage from several years ago would have been 44 MPG. Prior to the recent TB change... my milage was a pitiful 30 MPG and terrible power performance. It improved to about 40 MPG after TB change and a marked improvement in power.

Is testing pressure something I could have done at most any shop?

 

[RIP TDI]

If they have an exhaust back pressure gauge or generic low pressure gauge w/ suitable fittings.