exaust problems... 93 Z34

[disgruntled]

hello all! 93 Z34 3.4 auto. seems like i have 1 hell of an exaust leak coming from back of motor. starts, idles great. but when i rev up to the limiter, it almost sounds like a muffled backfire coming from back of motor and its blowing exaust smoke thru the hood. (just a very small amount, but enough to see). under driving conditions, noticable exaust hiss from under hood. (yes you can hear it). i guess my question is, should i look at manifold gasket, or donut? and just HOW do you get to these let alone see them? LOL anywhere i could get a diagram for exaust system front to back? i have checked everything from the front (that i can see anyway) to the mufflers and all is good. no leaks anywhere there. please advise and thank you!

[Husky]

I'm getting this from the front on my 1994. Odd.

[Mach10]

Here's an idea... Get some soapy water, and liberally coat the exhaust joints in question.

Jam a potato in each exhaust outlet, and jam a long-pointed compressed air blower-gun-thingy (I've got one, it's for clearing grit out of places) through one of them.

Have a friend slowly pressurize the system, and watch for bubbles.

Be advised, make sure the friend knows that an exhaust won't usually see more than 4-5psi... Putting 80lbs into the system will do a couple of things.

First, the potatoes in the back will bend time and space, changing instantaneously from being solid, and stuck in pipes, to becoming spongy and dripping down the opposite garage wall.

Second, you risk blowing out any still good joints on the system.

Set the pressure regulator LOW, like 10-15lbs and apply air slowly until you can hear it hissing out the joints (or see the bubbles).

If you don't have a compressor, jam the potatoes in, pull the fuel pump fuse, coat the joints with soap, and turn the engine over for 30 seconds or so. A motor is nothing if not just an air-pump. It will build pressure, but slowly. Keep cranking, pausing occasionally, until you hear a hiss.

If you don't hear it even after a minute or two of cranking, you have a BIG leak. Put the fuel pump fuse back in, and start the car for a second or two. You will hear (and see) a big leak REALLY quickly.

[Husky]

You're telling us to start our cars with potatoes in the exhaust? Gah!

JK. It actually sounds like a good idea, the first part. I won't be startign it though.

[Mach10]

I didn't think I was clear enough...

I would only consider starting it if I wasn't able to build any kind of pressure in the system.

Which would suggest a pretty big hole. This would become quite clear VERY quickly.

You'll also note I suggested not to try it for more than a couple of seconds.

AND FOR GODS SAKE KEEP CLEAR OF THE KILLER TATERS!