Leaky weld on Tomei UEL header
 

I have been popping P0171 codes randomly over the last month or so. Seems to happen mostly when I am sitting at idle.

Last week I bought and installed a slightly used Berk HFC front pipe so while I was under there, I decided to check everything out for leaks. Yup...just about every gasket/fitting was leaking to some degree or another. The slip joints on the Tomei were the worst, but I also thought I saw the weld on the passenger side header flange/pipe joint leaking but it was hard to tell with it installed.

I ordered all new gaskets and pulled the front pipe, over pipe and header off the car and rigged up a pressure test jig and pumped some low pressure air in. I'll be damned if there wasn't a pinhole leak in the weld!

Found a local guy last week that does awesome work welding stainless (fixed some cracks in the Berk FP for me last week) so I'll be paying him another visit tomorrow. Exhaust really blows (literally and figuratively)...almost as bad as plumbing! :mad0259:

[ame="https://www.youtube.com/watch?v=ycZxavgty34"]Tomei UEL header weld leaking - YouTube[/ame]

Nice test stand. You should consider selling to Tomei and others :)

How about a trade? My test jig for a shiny new Ace Header! :D I heard they pair nicely with the Edelbrock SC kit.

CSG has a nice Ace header that should be back from Ceramic coating soon for you :)

Never seen a fail on tomei, glad i went jdl

So it turns out to be a 1/2" long hairline crack across the weld at that flange/pipe joint. Welder should have it fixed tomorrow.
Now I need to figure out what to do about those leaky slip joints..besides buy a new header ( @CSG Mike @AceHeader-MT)..mines only 2.5 years old! :cry:
I'm open to suggestions!

A simple fix to maybe solve slip joint leaks (cheap and easy):

- Use a pipe expander, crank out the inner tube and apply furnace cement. Then insert back into joint.

Furnace cement will harden and look ugly but if you ever want to remove (or sell) just wire brush and it'll come right off, no damage to tubing.

Outside of that, I can't think of any simple solutions. Welding them would be a bad idea.

Good luck and hope it works out. Any questions let us know

Repair the weld. That's a quick job; should be very inexpensive.

Yeah, gave it to the Welder today so it should be ready tomorrow. Shouldn't be more than $20.

Not sure what you mean with the pipe expander...aren't those inserted into a pipe opening to stretch it to a larger diameter?
Once I remove the "brackets" that span from one side of the slip joint to the other, should the pipes just slide apart or is there tool I need to get them apart?
I was thinking that once I get them separated, smearing some High Temp Copper RTV in there as it should stay semi flexible...if it can stand up to the temps there. :iono:

$10...can't beat that. :thumbsup:

Slip joints are known to leak, especially when cold. You may find that once upto temperature they will seal themselves up.

Unfortunately there is no real solution other than to replace the type of expansion joint. I have Gruppe-S UEL headers will slip joints, its yet to go on the car im undecided what to do with them.

Yeah, I figured as much. All of my leak testing was done when they were cold. After getting the crack welded and not being able to get the slip joints apart without significant effort, I decided to put it back on as is since I found the true source of my P0171 codes (which is what started this whole thing)....a vacuum leak in my SC bypass valve, not an exhaust leak fooling the O2 sensor.
Now that it's replaced, all is good! :thumbsup:

Thats good news, glad you got it all sorted!

My only other suggestion would be to have the header ceramic coated but leave the slip joint section uncoated. My understanding is these joints work by differential expansion between the two pipes. Coating one side will just increase this differential.

...well thats the theory anyway

I had success on a slip joint years ago using Acousti Seal. Its basically a black tar that gets really thick under heat https://www.turnermotorsport.com/p-1...ound-5oz-tube/


I am looking at the groupe s header and will get a tube of this stuff if I go in that direction to seal the slip joint

Did you have to pull the slip joint apart to apply it? Mine's been on for 3 years so it may not want to come apart. I guess new would be the time to do it.

I'm curious as to why welding them is a bad idea. I understand the purpose is to allow for expansion (atleast I believe so) but I have seen many header designs UEL and EL with no slip joint or flex pipe so is it really needed?

From back in my Audi days the commonly referenced advice was to have 1 flex pipe somewhere in the system which most people ran it in the downpipe. Maybe it is because they use a cast manifold design but for welding the slip joints shut or on any other header without them would running a flex pipe in the front pipe or somewhere else suitable be a good idea?

The Acousti seal looks like a good idea, I don't know how long that would last for though?


@Detroiter, I think UEL headers are more susceptible to thermal stress due to their shape, the longer runners are going to expand more than the short. Most UEL headers have a expansion joint, the only exceptions I know on the top of my head are JDL and FT86SF headers.

I'm surprised this subject doesn't pop up more often on here. It doesn't take long to find a ton of threads on Impreza forums.