Exhaust Donut failure

[kennyrodgers]

Hi Folks.
I did the exhaust donut on my 1994 454 coach maybe 1500 miles ago and it's failed. I've got a replacement on order but can you guys tell me what I might have done wrong to cause it in the first place then I don't make the same mistake twice.
Thanks in advance.
Pete.

[Rickf1985]

Make sure the pipe is lined up with no strain side ways on it and also make sure the flange on the pipe is in good condition. Tighten the three bolts evenly. Are you using the right donut? Some are tapered on both side and some are tapered on one side and flat on the manifold side. You should have the later. Check your manifold to be sure. When I repaired my manifold and replaced that donut I had to loosen every clamp on the entire exhaust pipe front to back so I could get the flange in the correct position. When I get into the exhaust again I am going to cut the pipe after it makes the bend towards the back and put one of these in each side to give me some wiggle room and take the motor torque off of the exhaust pipes.


https://www.jegs.com/i/JEGS-Performance-Products/555/30771/10002/-1

[kennyrodgers]

Hi Rick.
To be honest I can't quite remember if the last one had a flat or not but I'm leaning toward not. It should be here tomorrow so I'll report back either way. Good call on the flexis and I think i might just do that myself.


I keep toying with the idea of headers but wonder if the extra expense is worth it. I've looked into it and I've read that people have had success with the cheaper Headman ones. My stock manifolds are pretty messed up as a P/O decided to kink the air pipes when they deleted the air pumps rather than plugging the holes. I tried to get the fittings out to plug them but they were too rusted in. We ended up welding them closed on the drivers side.
Replacement stock manifolds would be the same price shipped here from Rock Auto as the Headman Set (they are in stock in the UK )...then I gotta make up the pipes. I've also read that deleting the cat whilst going over to headers can screw up the o2 sensor ...and even then I wouldn't be sure of where to place it in the new system.
I'll go for the donut for now and keep ya posted and thanks once again.
Pete.

[Rickf1985]

Your O2 sensor should be ahead of the cat so deleting the cat would not make any difference. Using headers the sensor would go in the collector. Far enough back to catch all four cylinders on that bank. If you have o2 sensors before and after the cat then you might get a code but it still should not affect the way it runs. The second sensor is a monitor to tell the computer whether the cat is doing it's job. It is an emissions monitor to tell you that the cat is going bad. Headers will give you better bottom end but the Hedman headers are not all that sturdy and will probably only last you 4-5 years if you have any kind of rust problems there. As far as tying into the original exhaust, if you have dual exhaust it should be pretty easy. You eliminate the entire section that bends up to the manifolds and then all you need to do is fabricate a short pipe section to the header collectors. That is where those flex connectors would come in handy.

[kennyrodgers]

Hi Rick.
It's a single pipe system that's under there at the moment and there's only the one o2 sensor.
I'll keep it in the back burner for the moment and see how I get on with the new donut.
Thanks once again buddy.

[kennyrodgers]

Sorry Guys, forgot to update.
I got the new donut in. I think it was my mistake in that I don't have the original bolts and my gut tells me they weren't tight enough on the springs. I've done them up tighter this time and have got new correct bolts from Rock auto. I just need half an hour to change them out now.....
Cheers.