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Been wondering whether this is an exhaust leak or some kind of special modification done by the previous owner to make it "sound cooler". The sound appears to be coming from the manifold right underneath the distributor area (so closest cylinder to the front of the car). It's been doing this since day 1 when I bought the car in November. It's almost totally unnoticeable when idling but kicks in when under any kind of load. I also experience some hesitation and stuttering every once in awhile when driving so take that into consideration as well. Here's a video clip where you can clearly hear it (apologies for the wind noise). Thanks for the help.

 

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Discussion Starter #3
Exhaust leak.
Yeah that's what I was thinking. Old classic cars are a bit louder but not THAT loud. I tried to get some examples of a 280ZX NORMAL exhaust sound on YouTube but all I got was "ULTIMATE 280Z EXHAUST SOUND W/ PLATINUM HEADERS AND EDELBROCK POWER STEERING $$$$ CHECK IT OUT!!!!" Every search result.... Thanks. Now to plan out the big ass task of taking both the intake manifold AND exhaust manifold off. Hoping it's just a gasket issue and not some ghetto attempt at cutting into the manifold.
 

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You won't learn anything about an exhaust leak from a smoke machine, only an intake (vacuum) leak. Exhaust is moving out, vaccum/intake is moving in.

I can't hear anything unusual in the video at the top of this thread. An exhaust leak usually sounds like a "tick" sound because it's letting the pulse of each exhaust cycle past the gasket and into the open air. If you have a large leak, that could more of a "roar" (possibly subdued) as more exhaust pulses get past the gasket.

The most common cause of exhaust leaks in the I-6 engine is broken exhaust manifold studs at each end of the manifold. They break due to thermal expansion and contraction, and should be replaced with higher grade studs any time that you can do so.

Getting the manifolds off the I-6 is a very difficult job, but according to reports, it's possible. Some bolts hold down both manifolds at once, as they are positioned over the edges of both. Getting the manifolds off a turbo engine without pulling the head is essentially impossible.
 

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Discussion Starter #9
You won't learn anything about an exhaust leak from a smoke machine, only an intake (vacuum) leak. Exhaust is moving out, vaccum/intake is moving in.

I can't hear anything unusual in the video at the top of this thread. An exhaust leak usually sounds like a "tick" sound because it's letting the pulse of each exhaust cycle past the gasket and into the open air. If you have a large leak, that could more of a "roar" (possibly subdued) as more exhaust pulses get past the gasket.

The most common cause of exhaust leaks in the I-6 engine is broken exhaust manifold studs at each end of the manifold. They break due to thermal expansion and contraction, and should be replaced with higher grade studs any time that you can do so.

Getting the manifolds off the I-6 is a very difficult job, but according to reports, it's possible. Some bolts hold down both manifolds at once, as they are positioned over the edges of both. Getting the manifolds off a turbo engine without pulling the head is essentially impossible.
Yours sounds really "meaty" like mine as well? This is totally stock.
 

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Yours sounds really "meaty" like mine as well? This is totally stock.
It's tough to get much from recording an I-6 engine. Between the radiator fan and various other things, a noise has to be quite prominent to stand out. Also, it helps to use a separate mic and get it right next to the sound.

When I chase noises, I normally use an automotive stethoscope (they're cheap) and move it around the engine to get as precise a location as possible.
 

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Discussion Starter #11
If you guys are still interested in the sound issue I tried to get a better quality video. First cut is in the engine bay. You can clearly hear the sound, and I've narrowed it down to somewhere around the distributor (cylinder 1). The second shot is in the interior while driving. Almost sounds like someone put a poker card in my bike spokes lol. And it's only noticeably loud under acceleration as you can see.

 

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Been wondering whether this is an exhaust leak or some kind of special modification done by the previous owner to make it "sound cooler". The sound appears to be coming from the manifold right underneath the distributor area (so closest cylinder to the front of the car). It's been doing this since day 1 when I bought the car in November. It's almost totally unnoticeable when idling but kicks in when under any kind of load. I also experience some hesitation and stuttering every once in awhile when driving so take that into consideration as well. Here's a video clip where you can clearly hear it (apologies for the wind noise). Thanks for the help.

can you feel the exhaust with your hand? either a blown gasket or a hole in the manifold. try taking a look with a mirror?
 

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I can hear a bit of a tick in the first cut. Have you checked the belts and fan? What about checking the distributor for loose wires creating a gap that might have electricity snapping across it?

I may be confused by the location, but if it's not something on the front end of the engine, it's most likely a broken/loose exhaust manifold stud at the front end of the manifold.
 

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Start the engine up. Get a piece of 5/16" fuel hose that is about 3 feet long. Stick one end partially in your ear and take the other end and roam around the suspected noise area. Tip: keep the farthest end of the hose pointing slightly backwards and you won't get as much noise from the fan. Once you get to the noise itself, it should sound like it's very amplified so be prepared to pull it out of your ear so you won't hurt your hearing. This works just like a stethoscope IF you pull the probe off of the end. I prefer the hose vs. the stethoscope in this case because you can stick the hose into the gaps between the intake and exhaust a lot farther than a stethoscope hose. Also the stethoscope hose gets melted when it hits a hot manifold and the hose is more forgiving. A good stethoscope has it's place as well but not in this case. When installing the manifolds back on, after you bolt the exhaust man in place put the thick cupped washers on their appropriate stud and put the nuts on about 2 turns. Make sure the washers are as far away from the head as possible. This will allow you to slide the intake manifold between the washers and the head. Then install the upper bolts into the intake and tighten everything down. Using a 12mm wobbly socket on the lower nuts makes the job a lot easier. Also, remove only the vertical heat shield from the intake to do this job and by all means put it back in place when you're done. Good luck hunting. Z man of Washington
 
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