My fix for "vibrating idle" with pics

[mikepier]

A few weeks ago I was tying to troubleshoot a "vibrating" idle on my 99 XLT. I thought it was the engine, when in fact it was the exhaust system causing the resonation throughout the truck when stopped at a light and the truck in gear. I put a floor jack underneath the lower catalytic converter with a piece of wood and raised it putting just enough pressure on it, and when I put the truck in drive, the vibration was gone.
So now I thought if I tried to put some kind of brace on the cat, it would solve the problem, but when I put a piece of wire on attached to the frame, the vibration got worse, because it traveled through the wire to the frame.
So then I thought why not wedge a piece of metal between the 2 cats to "cancel" out the vibrations of each cat. This is what I ended up doing

Notice the 1/2" 45 deg elbow wedged in between the 2 cats. I had to use a crowbar to spread apart the 2 cats to get the elbow in there. The wire is just in case it pops out, preventing it from flying away.
When I started the truck and put it in gear, the vibration was significantly less, enough for me to notice. So if anyone is trying to troubleshoot the same problem, try this , it does not hurt.

 

[BrianDye]

I might have to try this, my 95 vibrates quite a bit when its idling my mirror kinda shakes lol its one of those things like no biggie, but it BUGS THE LIVING SH*T outta me!

 

[239]

Can you repost the picture?

 

[donalds]

This thread is from 2009

 

[239]

This thread is from 2009

Looks like Mike was on here just a couple months ago, so hopefully he can repost.

 

[J_C]

This is not really some mystery with a special fix needed. It didn't vibrate from the factory (unless defective?) so odds are all you need is a new exhaust hanger, unless your exhaust has been redone and is now off-spec, needs adjusted to regain the clearance it used to have.

It could just be that you have a heat shield that is (was) welded on and the welds have rusted out, then you can just take wire or a metal strap to secure it again, unless you're really good at welding [thin metal exhaust parts] and feel capable of welding it back on.

 

[239]

This is not really some mystery with a special fix needed. It didn't vibrate from the factory (unless defective?) so odds are all you need is a new exhaust hanger, unless your exhaust has been redone and is now off-spec, needs adjusted to regain the clearance it used to have.

It could just be that you have a heat shield that is (was) welded on and the welds have rusted out, then you can just take wire or a metal strap to secure it again, unless you're really good at welding [thin metal exhaust parts] and feel capable of welding it back on.

I definitely need new hangers since mine are stock. Only problem is they’re obsolete and I can’t find them anywhere, so I’ll have to make my own or find a universal replacement.

I’m sure the exhaust needs replacing too. I wonder if the cats are still intact after all these years. I wouldn’t be surprised if they’ve broken into pieces and are rattling around.

 

[donalds]

Aaaaahh just let it vibrate off then put straight pipes out the back lol

 

[239]

Aaaaahh just let it vibrate off then put straight pipes out the back lol

I’m sure my neighbors would love that. My fellow motorists at the drive thru would too lol

 

[J_C]

You might be able to mount universal hangers on the factory studs unless too rusted out, or some big self tapping metal screws with a starter hole somewhere convenient, possibly a backing plate if the metal is compromised.

CATs tend to last a long time unless there is some engine problem that fouls them. On mine the muffler recently rusted out first, I thought about replacing just it but decided on the whole cat-back, the pipe with resonator too. Mixed feelings about that, the (Walker?) replacement is just aluminized metal so it may not even last longer than the stock pipe if I were to leave it on, but something stainless could cost multiple times a much.

I contacted a few local muffler shops asking if they could custom bend a stainless pipe for me and they acted like stainless was alien technology, they don't even carry it. I could acquire a length of pipe myself then take it to them but meh it starts getting to be as much of a hassle and more expensive than just replacing the pipe again... was only $65 IIRC, at least the muffler is stainless.

 

[239]

You might be able to mount universal hangers on the factory studs unless too rusted out, or some big self tapping metal screws with a starter hole somewhere convenient.

CATs tend to last a long time unless there is some engine problem that fouls them. On mine the muffler recently rusted out first, I thought about replacing just it but decided on the whole cat-back, the pipe with resonator too. Mixed feelings about that, the (Walker?) replacement is just aluminized metal so it may not even last longer than the stock pipe if I were to leave it on, but something stainless could cost multiple times a much.

I contacted a few local muffler shops asking if they could custom bend a stainless pipe for me and they acted like stainless was alien technology, they don't even carry it. I could acquire a length of pipe myself then take it to them but meh it starts getting to be as much of a hassle and more expensive than just replacing the pipe again... was only $65 IIRC, at least the muffler is stainless.

Muffler shops in my area aren’t too reliable either and I hear mostly rip off stories about them. I’ll just buy some Dorman manifolds and walker cats to keep it as stock as possible, then I’ll have my regular shop bolt it all on.

The rear hangers should be easy to replace with a universal part.

But the square hanger by the transmission will have to be cut from a larger hanger and custom made. It has a part number on it but I couldn’t find a replacement anywhere.