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Discussion Starter · #1 ·
I'm sure someone's seen this and commented on it before. Just noticed for the first time. Had my son start the truck while I was under the hood. Noticed a puff of black smoke upon ignition under the hood near the back of turbo/air intake vicinity. Only happens on startup. I'm thinking that there's a gap in the mating surfaces where the turbine elbow meets the exhaust downpipe and exhaust is escaping. Recently replaced the turbo and had a little trouble mating the original turbine exhaust elbow back onto the downpipe. Could be the down pipe/eblow fasteners aren't tight enough. Might take a vid and slow it down to see exactly. Thoughts?
 

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It's likely an exhaust leak. Could be that the exhaust elbow and downpipe have a slight gap when cold, but may make a better seal when hot and the components have expanded. The obvious problem is trying to diagnose an exhaust leak while the engine making noise and the fan is running. Are you familiar with a blow bag for plumbing? If you have access to an air compressor, you might be able to rig up a sort of blow bag at the exhaust tip. Let the blow bag seal the tip, pump air into the exhaust tubing and listen for leaks around the elbow and downpipe. Might be a novel way to test for leaks.
 

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Might need to pull the fender liner and get a closer look. Diesel exhaust leaks are usually not hard to find. Just look for soot. Probably a v band clamp. Before you decide to tighten them up loosen them off and make sure they are broken free prior to retightening because you would most likely be tightening it against the rust and not actually fix anything and possibly break the threaded coupling.

I usually spray some WD40 or something similar on them prior to playing with them. The lube will help it tighten back up.
 
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Discussion Starter · #4 ·
It's likely an exhaust leak. Could be that the exhaust elbow and downpipe have a slight gap when cold, but may make a better seal when hot and the components have expanded. The obvious problem is trying to diagnose an exhaust leak while the engine making noise and the fan is running. Are you familiar with a blow bag for plumbing? If you have access to an air compressor, you might be able to rig up a sort of blow bag at the exhaust tip. Let the blow bag seal the tip, pump air into the exhaust tubing and listen for leaks around the elbow and downpipe. Might be a novel way to test for leaks.
Thanks Chris. I think it does fix itself (mostly) after it’s at running temp. I might just go take it to a local exhaust guy in town and have them realign.
 
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If you have high miles look for cracks under exhaust manifold.
When I went to flip my manifold for compound install I discovered I had cracks in the manifold underneath it that could not be seen before I removed it.
If you remove anything, remove the turbo to get a better look at things.
 
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Discussion Starter · #6 ·
If you have high miles look for cracks under exhaust manifold.
When I went to flip my manifold for compound install I discovered I had cracks in the manifold underneath it that could not be seen before I removed it.
If you remove anything, remove the turbo to get a better look at things.
There's low miles on the truck, 89K. I'm pretty sure its a leak at the elbow/downpipe. Thanks
 

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Discussion Starter · #7 ·
Anyone have an opinion on using an exhaust flange gasket to fix this leak at the elbow? See freeze frame pic I took of a slowmo video as the puff of smoke comes out of elbow/downpipe.
 

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Anyone have an opinion on using an exhaust flange gasket to fix this leak at the elbow? See freeze frame pic I took of a slowmo video as the puff of smoke comes out of elbow/downpipe.
It's not very clear. But have you removed the band clamps and checked them too? They can distort or crack and become problematic such as you're seeing.
 

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Try loosening the downtube where it connects to the rest of the exhaust. See if that buys you enough wiggle room to close the misalignment between it and the elbow.
 

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Discussion Starter · #11 ·
Yeah I’m just going to get a local exhaust shop sort it out. Need a break for the minute from messing with the truck!
 
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Yeah I’m just going to get a local exhaust shop sort it out. Need a break for the minute from messing with the truck!
I think all of us have been there before.
 
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Discussion Starter · #13 ·
BTW - I fixed this exhaust leak by just tightening down the 2 elbow flange bolts a whole lot. It seems that I way under torqued all the fasteners - from my turbo-back after replacing it a few months ago. As a result, it looks like my EGTs are now 70/100 degrees lower based on some benchmarks I took prior. Power seems to be up too unless it's in my mind. However, in theory, this all seems legit if the leak is now gone. What say you all on this, sages of the 2nd Gens??
 
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