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exhaust leak source, repair difficulty?

L

Lifespeed

New member
My son has a 2001 GTP which has received a lot of maintenance, so it runs and drives well. It has had an exhaust leak for a while, but when I drove it today I noticed it has gotten pretty bad. Also the lower motor and transmission mounts have to be shot at 182K miles, although the upper dog bones are new (cheap and easy).

At first it would only leak when cold, making a ticking sound. Now the ticking sound has become more of a roar, but only under heavy throttle. Initially the ticking made me think cracked exhaust manifold as it sounded like a single exhaust port. Maybe it has just gotten worse, opening up under pressure. However, the smell seems to be the smell of exhaust *after* passing through the catalytic converter.

Any suggestions of where and what to look for, repair difficulty and expense? How hard are those lower motor mounts? Is it likely the bad motor mounts have contributed to the leak, or do the just let the motor move too much and vibrate the chassis at idle?
 


sounds like the factory flex gave up on ya. its part of the down pipe where it bolts to the rear manifold.

if its cold in the morning fire it up watch for the cold exhaust to show it self. if you look deep between the firewall and rear manny, you'll see the two bolts for the dp. would see it leaking just under that part.
 
Scottydoggs said:
sounds like the factory flex gave up on ya. its part of the down pipe where it bolts to the rear manifold.

if its cold in the morning fire it up watch for the cold exhaust to show it self. if you look deep between the firewall and rear manny, you'll see the two bolts for the dp. would see it leaking just under that part.
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Thanks! I thought this might be something that was well-known among Grand Prix owners. I'm guessing this part isn't available from GM? Would you be able to direct me to a quality replacement? It isn't this crossover from Dorman, is it? It isn't flex . . .
 
dorman should have a catted down pipe direct fit. the flex is not a mesh flex, its like sliding metal parts.

being your a 01, dont get a hi flow cat. it will set a cat code on ya.
 
Scottydoggs said:
dorman should have a catted down pipe direct fit. the flex is not a mesh flex, its like sliding metal parts.

being your a 01, dont get a hi flow cat. it will set a cat code on ya.
Click to expand...

I need to replace the piece with the cat in it to fix this? Uh-oh, I'm in California. It isn't always the case that a replacement cat is California-legal, even if it isn't "high flow". They have to meet OEM specs.
 
Lifespeed said:
I need to replace the piece with the cat in it to fix this? Uh-oh, I'm in California. It isn't always the case that a replacement cat is California-legal, even if it isn't "high flow". They have to meet OEM specs.
Click to expand...

you could buy a off road pipe and have a shop weld back in the stock cat.
 


My son and I crawled around under the car on jack stands. With the engine cold and loaded against the torque converter with the brakes on, I ran my hand around the crossover pipe flanges, as well as the bellows (flex?) at the downpipe-to-cat flange. Unfortunately the tick wasn't that loud at the time, and I wasn't able to isolate the source of the leak. The fact that it ticks sure makes me think of an exhaust port leak, like an exhaust manifold gasket between the manifold and head, or a cracked exhaust manifold. If I can't figure out how to confirm where the leak is coming from I may take it to an exhaust $hop. I think my brother bought this car as a one year old used car in Texas, so maybe we're in luck as far as parts availability - CA parts aren't available from GM.

A confounding symptom was when I pushed the car into boost and heard an accompanying roar, and a slight loss of power, along with a rhythmic chuffing noise synchronized with the engine power dropping. Am I perhaps confusing two different problems? Could an intake manifold gasket be blowing out under boost? Any good way to confirm this?

At this point I'm going to replace the lower motor mounts so they're all new, and remove any confusion from the excessive engine movement, although to be honest the movement isn't really bad with the upper mounts replaced.
 


Apparently a good trick is to plug one of the exhaust pipes and blow into the other with a shop vac. Spray soapy water around the suspect areas. I'll give it a try.
 
you can get a decent replacement CA compliant cat from Rock auto. they are having good price lately. and I think a lot of the aftermarket CARB cats have an improved inlet and no U bend too.
 
scan for knock retard and timing advance.

wot you should see at least 16 degrees. with no kr. if theres kr the timing will be lower.
 
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