Loud noise and gas smell. Exhaust manifold?
 

My Z is making a bad sounding noise – videos linked below. It is hard to hear from the engine bay, but very loud from inside the car and underneath. The sound is almost always there, but differs with changes in RPMs. It went away at one point on the freeway going a constant speed, but came back minutes later while still maintaining a constant speed. Exhaust smells bad, gas smell at the right rear wheelwell. No noticeable loss of power or any other symptoms.

This started after a track session on a hot day. The car was in storage about 9 months prior and I drove it about 100 miles before taking it on the track with no problems. When I started it up for the second session, it was making the noise, it smelled funny, and it threw CEL P2A03. I previously have had issues with P2A03 and P2A00 codes, but last week replaced both upstream o2 sensors with used ebay sensors and all emissions tests were ready before going on the track. I reset the light when I left the track and the Catalyst and o2 sensors are both showing as green now, although I'm still waiting on EVAP readiness. The bolts on the cats are tight and I don't see any obvious cracks. The cats are Z1 Motorsports brand with only about 3500 miles on them, most of which were low RPM miles driving cross country.

While being stored, the gas tank was full of 93 with Sta-bil additive, and I was on this same tank of gas when the issue occurred.The car has 56K miles. It has a Nismo intake and exhaust, Motordyne XYZ pipe, Z1 HFCs, and an Uprev tune (although the tune was meant for ART pipes, but those are too much hassle with our annual inspections). I had the P2A03 and P2A00 codes even with the ART pipes. I used new gaskets when installing the Z1 cats.
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Any ideas? Exhaust manifold?
Thank you.

I just realized I blew my differential bushing on the same day I heard the noise, so I'm thinking that could be the source of the smell. Could the black goo from the bushing possibly smell like gas when heated up? If so I can just focus on the noise and forget the smell.

Diff bushing wouldn't smell like gas, The gas smell is probably related to an exhaust leak. I can't really tell from the video but one of your o2 sensors could be loose?

That black primordial ooze in the rear differential bushing doesn't smell like gas when it's heated (or when it starts smoking). Ask anyone that has attacked that thing with a power drill or reciprocating saw. :bowrofl:

As far as the noise and the gas smell, I got nothing for you. I guess the obvious would be an exhaust leak somewhere. :dunno:

Thank you! You were both right, there was an exhaust leak behind one of the cats, even though the bolts were very tight. As for the noise, the Z1 HFCs have two o2 sensor locations per cat (before and after the catalytic filtration) and they come with "bung plugs" as Z1 calls them :icon17:. One of the bung plugs was slightly loose. I can't believe it caused so much noise in the interior of the vehicle. I'm guessing the second bung location allows relocating the upstream sensors to the cat itself to make them easier to service?

I will unfortunately have to attack the rear differential bushing soon. Not looking forward to that.

Nice, glad it was something simple and nothing was cracked haha.

Getting that old rear diff bushing out is a 'fun' job. If you aren't going to buy a removal tool, I recommend getting a set of wood chisels from Harbor Freight. There are plenty of walk-thoughs, but I basically cut/drilled/hammered as much of the rubber out as I could, then cut a small notch in the bottom leading edge of the bushing casing and used the chisel + hammer to propagate the cut. Once you are able to fold the cut up you should have enough space to fit the smallest chisel between the casing and the subframe. Hammering the chisel into that gap may mare up the subframe a little bit so I also had some sandpaper on hand, but there wasn't much damage, and it only took a few hits on the chisel to drive it all the way in and bend the entire length the bushing casing until the old bushing slid right out.

While not exactly fun, some sick gratification can be had from using brute force and power tools in an unconventional manner to remove that POS bushing.

+1 on the drill, saw, chisel method :thumbup:

Wait a minute... so is this whats all over my exhaust pipe and diff cover? Where's the best diy thread to replace this thing?
https://cimg2.ibsrv.net/gimg/my350z....bf0096fc82.jpg

Yep, the bushing was silicone filled from the factory, but it eventually leaks out.

As for the best DIY threads, I read every one I could find here and on G35Driver and compiled all the relevant info in my head. I had access to a lift which gave me a better view of the bushing, but also meant I needed a buddy to help drop and re-install the diff. If you're doing it on the ground you can use a jack maneuver the diff, but it'll be tougher to hack at the bushing. If you want to make your own tool (makes removal much easier, especially if you're doing it on the ground) check out THIS thread. Otherwise, google it and read a few different threads and watch some youtube videos. There's no 'right' way to do, it's just a matter of figuring out what will work best for you with the tools you have.

Thanks for that :thumbup: 15 years and nearing 100k miles. Time was probably a factor more than mileage.
So, I haven't noticed any issues at all. What's gonna happen if I leave it alone rather than replace it?

Yeah, I think I've read of them going bad as soon as 60k, but it's a gradual degradation so you don't really notice. It won't cause any major issues, the rear end will just have a little more slop and be more prone to wheel hop on hard launches. No big deal, but it's definitely a nice (and relatively inexpensive) improvement, assuming you don't value your time :icon17:.

In addition to what Sparta mentioned, I heard/felt a noticeable "clunk" during hard shifts with my blown diff bushing on my G. All the ooze was just about gone when I removed it and it was really dried up.

On the Z, there was still a good amount of lubricant left in the bushing and I didn't really feel any noticeable effects up to when I replaced it, but it was still blown since there was a black drip coming down the subframe.

My diff blew it's wad. Huh huh.
I've got a 4 door awd z so wheel hop is not an issue but I wonder if this bushing is responsible for the slight shimmy that I and several other techs have been attempting to pin-point for near 2 years. I went from one pair of tires to conti's dwso6, road matched then hunter road force balanced and then had'em trued, The fx drives like it's on glass but at highway speed and depending on the section of road, I get the left-right "shimmy shuffle" in the steering wheel. It's so much better now, almost completely gone but after all I've been through, it's still there.
I wonder if the bushing gave up back then, 2 years ago, when I decided to keep the fx and started to modify it. One could say it had something to do with what I did but I and the other techs doubt that. This could be it, it just decided to truly fail in spectacular fashion all over my undercarriage. It's possible:dunno:.

What conditions bring out this shimmy? There are two more bushings on the front of the diff housing that are much less prone to failure, so the diff is still pretty well fastened to the subframe. I guess the blown bushing could allow more side-to-side motion, but again the front bushings would help combat that motion, with the rear bushing controlling up/down pivoting relative to the front bushings.

In this pic, there are the two bushings at the bottom (front), and the stud on the back goes into the rear bushing that's pressed into the subframe (and secured by a nut).

https://cimg8.ibsrv.net/gimg/my350z....8ade42d5a7.jpg

Nice pic. Depends on the speed and the road, mostly the road though. It's really odd. At first I thought it was the kumho's I had, prior to the conti's I have now which are great. That brand does still suck but they weren't responsible for the shimmy.
It's possible. Everything else is good. We started looking at the wheel and spacers but no issues were found and they are of good quality. I recall a friend having similar front end issues and it turned out to be something in the rear suspension but it was a long time ago and I cannot remember the specifics.
I guess I'll find out the hard way and replace it. :icon32: