# Buzzing intake sound



## cajunlte (Sep 22, 2012)

1997 Nissan D21 HB
I have completely solved my overheating issue and have even resolved my MAF issue. My issue is that I now have what seems to be a buzzing sound when I increase the throttle or when picking up speed until I get to about 2800RPM at which time the engine seems to de-fuel. The noise is definitely coming from the intake after removing the air cleaner assembly. 

Any idea what would be causing this? Bad injector?

I am also not getting any codes.


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## smj999smj (Jan 1, 2006)

It's tough to identify "noises" when you can't hear the noise. Most buzzing noises on these vehicles occur from the exhaust heat shields. I've never heard of fuel injectors "buzzing." If anything, they will make a "tapping" noise. I also don't know what the term "de-fuel" means? If you feel you are losing fuel pressure, install a fuel pressure gauge to confirm the fuel pressure is in-spec and not dropping-off at 2800RPM+.


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## cajunlte (Sep 22, 2012)

I will take some video of the condition and post the link to it. Not a ticking noise, but more like an exhaust leak that is coming from inside the intake. The de-duel reference is to the loss of power after about 2800RPM+. She runs smooth below that. The fact it is not throwing a code has me scratching my head.


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## rogoman (Dec 16, 2004)

cajunlte said:


> The de-duel reference is to the loss of power after about 2800RPM+. She runs smooth below that. The fact it is not throwing a code has me scratching my head.


The loss of power at around 2800 rpm points to a MAF problem that may be going into 'fail-safe' mode.


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## smj999smj (Jan 1, 2006)

The question is: is it losing power at 2800 RPM or is it limiting the RPM at 2800 RPM? Fail-safe mode limits the RPM to approximately 2500 RPM, at which point the engine will start surging heavily. If it is just losing power, I would look at fuel pressure and exhaust back-pressure first.


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## cajunlte (Sep 22, 2012)

I would say it surges while only under load. In neutral she will go above 3kRPM. Here is the video of the intake noise. Cleaned the MAF sensor even though it is not throwing a code and is new with maybe 10 miles on it. I checked the routing of all vacuum tubes.


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## smj999smj (Jan 1, 2006)

Sounds like the timing chain jumped a tooth and the valve timing is retarded. You might want to do a compression test or confirm that the cam and crank are in-time.


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## cajunlte (Sep 22, 2012)

Cool. I will borrow a timing light from my buddy to check the timing. If it jumped I assume that will require me to remove the front cover and check that both the top and lower sprockets are lined up with the dark link on the chain?


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## smj999smj (Jan 1, 2006)

If it jumped, you will likely need new timing guides and a tensioner. Most would get a timing set with new gears. While apart, remove the oil filter and spray carb cleaner through the oil port on the face of the block (behind where the tensioner mounts) and follow with compressed air until it blows clear out of the oil filter adapter. One of the main reasons for timing chain noise and/or jumping on these engines is that debris in the oil channel restricts flow to the tensioner, causing slack in the timing chain.


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## cajunlte (Sep 22, 2012)

Any recommended kits available on the market that would contain all necessary parts to completely swap all timing elements? I see all the parts in the part catalog.


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## smj999smj (Jan 1, 2006)

Rockauto.com has several sets starting at $55. Have heard of some issues with aftermarket parts, though. They have a Sealed Power (a division of TRW) set for $100, but it doesn't come with the oil pump gasket nor oil seals by the looks of it.


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## cajunlte (Sep 22, 2012)

Not a timing issue. About 11 at idle so it hasn't jumped. Haven't checked compression, but she runs ok at idle and can even be accelerated to 3000-4000rpm not in gear without the hesitation. Seems to happen only under load. I am almost at the point of taking it to a import mechanic to help in troubleshooting.


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## TheRepairMan (Jun 30, 2009)

It looks and sounds like, by video evidence and your description, that the exhaust system may be restricted. Having had MAF problems it could have actually damaged the catalytic converter thus causing these new symptoms. Most exhaust shops can drill a test hole and mount a pressure gauge upstream of the cat to see if that's the problem or not.

-R


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## smj999smj (Jan 1, 2006)

They don't need to drill a hole. There are exhaust backpressure testers that screw into the upstream O2 sensor bung. Many auto repair shops have them as well. Definitely a good idea!


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## cajunlte (Sep 22, 2012)

You know this makes perfect sense. The noise really doesn't start until the engine has warmed up for a few minutes. I would assume that the cat only starts causing the issue after it begins working properly causing to much restriction. Looks like I know what I will be doing tomorrow morning.


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## cajunlte (Sep 22, 2012)

Ouch! I just looked up the OEM price on this bad boy. No way in hell....


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## smj999smj (Jan 1, 2006)

A clogged cat is clogged whether it is cold or hot and its affects would be immediate, not after it's warmed up. Exhaust back pressure testers actually are used with a cold engine as the hose on the tester will melt if the exhaust gets too hot. I would definitely make sure the cat is bad before replacing it...and aftermarket cats are a lot cheaper than OEM. Try Rockauto.com if you need one.


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## cajunlte (Sep 22, 2012)

Brought it over to a highly recommended import place in the area and they immediately knew it was the timing chain. Was told that the sprocket has lost a few teeth. They will do the complete kit and clean all components for $675. Considering how hard this is for a rookie, I am more than happy for them to handle.


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