General exhaust & doughnut gasket question...

89 XJ 4.0

Anyone ever have on of these fail and cause a leak? I know I have an exhaust leak of some sort. At idle it's a chuffing sound (more like a pft, pft,pft) than a ticking (tick,tick,tick). I know the tick sound of an exhaust leak but this sounds like it's a little farther down the system...

I want to pull and replace the exhaust system this weekend (it's thrashed) and I don't want to buy a new exhaust manifold if it's not cracked. I'm hoping it's the doughnut gasket that's leaking and I just have to replace that, the pipes, the cat and muffler.

Also, does anyone know if the chain stores sell the the front pipe & tail pipe pre-bent (even if it's a spec order part)? It's checked online and it's unclear and the kids at my local autozone are no help.

If I pull everthing down myself and find I need to replace the manifold too I'd just as soon do it all myself rather than try to drive to a muffler shop with NO EXHAUST and have them do the bends...

Thanks

Shucks had the tailpipe in stock - can't remember the exact price, but it was under $20, and a perfect fit. They also had a generic doughnut which was a perfect fit.

Before you get too happy with changing parts, retorque everything. It's fairly common to have exhaust leaks due to loose manifold bolts - and that's something you can fix in a half-hour or so for free!

5-90

Hate to be a berror of bad news ,but the 4.0 is famous for its cracked manifolds. As far as the front pipe I picke up one from napa for 12.99 .If you end up replacing the manifold I recomend you pick up the pace setter header set for that. It will come with everything you need all the way to the cat. flange(3 pc set). Gets you better gas milage ,power, and far less likely to crack than the OEM manifolds. I found mine on ebay for 199.00 and it made a world of difference,throw on a flowmaster muffler and she will sound beefy.And yes, I have seen the donut gasket go bad before,so hopefully thats your problem.

5-90 said:

Before you get too happy with changing parts, retorque everything. It's fairly common to have exhaust leaks due to loose manifold bolts - and that's something you can fix in a half-hour or so for free!

5-90

Click to expand...

That was my original plan but it looks like I need to remove damn near everything on the right side of the block to get at the bolts to re-torque.
I thought I might as well replace things since I'll have room to work. If the manifold IS cracked, which sounds like a given, I'll already be half way there.
At that point I might as well replace the whole system.
Besides..the cat is original and REALLY banged up. The XJ's been sitting for a couple of years so now I gotta get it smogged to get it reg'd. I figure a new will help...

having just replaced my exhaust manifold - you can get to all the bolts if you remove the following...
1) Air Box
2) Fuel Rail (Make sure you've got some Injector O rings)
3) Heat Shield

However, you can torque up everything other than the manifold without removing anything at all. Assuming the exhaust system is in OK condition, I'd start there, and I'd also torque up the manifold bolts you can get to by just removing the air box - a "wobble drive" on a 7/16ths and 9/16ths socket is a good thing.

If you've had the exhaust on for a long time, it may be worth looking for soot marks on the joints you can see...

True about manifold cracking - but the last two times I thought I'd lost the manifold, I fixed it with a torque wrench.

If you take down the airbox, then use a couple extensions and a 9/16" shorty universal socket, you can reach them all. The studs are pretty accessible.

I'd check all this before I started thinking about changing anything - like I said, at least it's free. If it doesn't work, you're only out a half-hour or so, and you don't end up with that sinking feeling you get when you put a lot of time/money into a problem that you somehow managed not to fix...

5-90

I'll give 5-90's suggestion a try...I try it with just the airbox pulled only...

I hate to have to remove the injectors or rail since I installed new O rings last weekend.

Thanks guys...

Well, I had a fun weekend.
Not only was the manifold cracked at # 5 & #6 (almost completely around the pipe!) the donut was ALSO shot...

I pulled everything off from tailpipe to block. Big job but great experience.

Now I'm sporting a new Motormite Exhaust (can't afford a Borla, etc) and new front pipe. I bolted the old cat/muffler/tailpipe assy back on just to test. What a bloody difference. Obviously it's more quiet but it also idles much better.

I have a Summit OEM style cat in the mail (I want it to bolt right up to the 4 bolt flange) and muffler waiting in the wings.

I'm thinking about taking the cracked manifold to a weld shop to see if it can be repaired and/or strengthened since from what I read, this new one will eventually crack too.

i just replaced my exhaust and torqued everything by the book and it sounds worse than before i started. the manifold was completely shot when i got it off, so i replaced it and replaced the down-pipe doughnut with a new one. i think that it is now leaking at the doughnut, since that is where the sound seems to come from. have i just not torqued the doughnut enough or what? i took everything else back off and re-torqued everything and the leak is still present. what have i done wrong?