Woosh or pressure purge/release sound under load or deceleration only

[brycebba]

So I took the engine out of my 99 Yukon, rebuilt it, and had it swapped into my 97 Jeep Wrangler. Unfortunately the shop that worked on it is 450 miles away from where I live now so they have been helping remotely as much as they can but obviously that's difficult.

600 miles in and I started suddenly hearing a noise under load or deceleration at higher rpm (maybe 2500+) that sounds like a sudden loud pressure release or woosh sound that repeats every second or so and *seems* to be coming from the passenger side. There is no power dip whatsoever, it still pulls strong. There are no codes at all besides my egr codes (waiting for the egr tube to be fabricated so it's temporarily blocked off at the intake manifold and header but valve is still plugged in).

You can kind of hear the sound in this video but I will try to get a better video tomorrow that is focused on the noise. This video was diagnosing to see if it was fuel pressure related which it's not.

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What I have checked
--fuel pressure is great and does not dip when these pops/woosh/pressure release starts happening.
--I haven't been able to find any kind of vacuum leak
--I haven't been able to find any exhaust leak that would introduce air and combust in the exhaust
--egr bypass at the header and intake manifold are totally sealed, plus this has been bypassed since about 25 miles because it kept blowing the hose my mechanic used.
--I thought I found a plausible explanation when I found the rear most passenger side plug to be extremely loose but tightening that up made no difference. I also made sure the rest of the plugs were tight.
--timing is spot on and is verified via a mechanic grade matco scan tool.
--distributor is tight and gear is in great shape (also not convinced this is a misfire since there are no codes and there is no noticeable stumble or hesitation when the sound/symptoms act up)

I'm sure I will remember other things I have checked.

In case it's valuable info, most sensors are reused from the Yukon which ran great before getting torn apart and rebuilt. The engine runs great even when this sound/symptom is happening. The computer has been tuned by Black Bear Performance to remove anti theft and post cat O2s but other than that it's a stock tune. Everything was rebuilt, assembled, fabricated by a custom jeep shop that has done these before.

I'm grasping at straws and am very depressed because my new toy is broken

Any help or ideas for me to scientifically/systematically test would be great.

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[brycebba]

So I did another exhaust leak check today and found a leak where a tube on the passenger side meets the flange. The leak in the video was more pronounced when revving or using my shop vac up the exhaust. I have to find someone to weld it up. I'm doubting this small leak is the source of my loud sound though but maybe it's sucking air in somehow?

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[brycebba]

I'm getting the leak welded tomorrow so hopefully I will see some change in the sound and it is somehow related to that leak

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[brycebba]

Ok, as far as I can tell, no more exhaust leaks. I think the sound is happening less but maybe not. it definitely stumbles when it does it hard BUT THROWS NO STUPID CODES!!! What should I be looking for? Please any ideas?

 

[Chris253]

I had this problem once.

Nice warm morning, getting ready for a hot day. Tested the air conditioning. It works, cool, turn it off keep driving. I then heard that sound.

Long story short, the air conditioner failed at that moment and after a ton of work, unplugging the air conditioner solved it.