Farty noise from exhaust
 

The car is making a farty sound from the exhaust. I don't mean Honduuuh farty, its almost metalic. Imagine sticking your toung out and making a fart noise.

It is load dependent, and happens at all RPMs. I can expecially hear it when the sound is bouncing off a wall coming back at me.

Specs:
1996, stock 1.8
2560, 3" turboback (strait pipe with a 16" long 4" diameter can, no cat)
DIYMS-I

I don't know if I am imagining it, but the car seems slower. I'm thinking I might have slipped a notch on the timing belt, but that's just an early guess.

Thanks

EDIT: It almost sounds like an exhaust leak but its coming from the tailpipe.

sounds like a misfire from description

I forgot to note that the sound isn't there at idle... at least not loud enough to hear. Thanks for the idea though, I'll throw a timing light on there.

Happens at all RPMs and loads? What is your plug gap?

Forgot, but they have been gapped. And the car has been fine up until now.

Sounds to me like you have a weak or dead cylinder. Try running the car for a minute and spray a little water on each exhaust header pipe. If one does not sizzle or sizzles less than the others, you have found the problem cylinder.

Don't think its 3 cyls, it idles fine

So did mine, but it had a cracked piston, and made the same farty noise. Got the same farty noise when I had a weakly firing cylinder also.

Stop second guessing and see if you lost a cylinder somehow.

Edit: Mine also idled normal with both occurances. Noise began when under a load.

Bring it by and lemme have a hear at it :P

I'm thinking its a spark plug, smells heavily of gass

Der, you going to boost for boobies?

Confirmed that all cylinders are indeed firing.

how rich is it? they sound like that when they get pig rich.

Just checked, about 17:1 at idle, like it's always been.

I'm starting to fear the worst here, guys. I will be getting a compression test to determine if I burned a piston or something.

i mean when it farts. and thats way too lean at idle.

Thanks, I will richen it up.

AFRs are ~ 14 when it's revved up slightly and the farting occurs. AFRs are fine under boost as well...

I reread your description and it makes me think exhaust leak.

Cars for boobies?! Haven't heard of this'n. I am getting a quote for exhaust tomorrow and maybe getting it done shortly after. When is this thing happening?

Also, I have a leakdown tester but it might be bad, I got a popping sound while using it last time and I'm thinking the hose is bad. We can always turn the compressor reguator to 15psi and plug the line in and listen for sound :P

Compression check today. Will post the results when I get them.

If there's no compression on a cylinder, I assume that it's either a cracked/melted piston or could it be a burned valve or something?

Der, it's on the 16th?? Something like that. Or the 22nd. I don't remember. Check it out on facebook, just search boost for boobies and it will come up. It's a charity event held by MAP for Race for the Cure. Dyno spots will be auctioned off at 9:45am and some time in the afternoon...

Hopefully this will be fixed by the 16th, but I fear the worst.

EDIT: So, if my compression is low in 1 cyl, it means that there's a problem with the rings or something. If the compression is just not there, it means that there's a problem like a valve or burned piston. Correct?

Assuming the compression is good, what could it be? My friend said the turbo, but I'm thinking it's too in time to be a rattling compressor or something. All cylinders are firing. Started it cold this morning to move it and the sound was pretty bad. MUCH more noticeable then when it was warm. This leads me to believe that it's probably a ring or piston slap or something along those lines.

Can't make that, I work weekends. Good luck.

Oh and if it's the block or what not, I have a bottom end that's just sitting around (head is being pulled).

Really? Details on the block? If this compression test comes back shitty I will be extremely interested.

Brain, I don't think it's an exhaust leak because the sound is coming from the tailpipe.

BTW, since I started it this morning, the sound is now noticeable at idle.

Can't you post a soundclip?

Didn't have time to get one. Got home from work at about 8:30 and had shit to do. I will try to get one tonight.

Block is out of a 97. I can't remember how many miles it had, but it was quite a few. It ran fine when I was autocrossing it before I pulled it for the forged block.

How old is your exhaust? Did it possibly blow out a baffle in the muffler?

Compression is fine across all cylinders - in the 150s.

Exhaust is brand new. No baffles either, it's just a strait-through can.

IIRC its new and he had a friend fab it up for him.

I'd be willing to bet its something to do with the exhaust, seeing that you just put it in recently.

I feel like it's too rythmatic to be an exhaust issue.

EDIT: Ok, let's brainstorm - what about the exhaust could it be that would cause it to be directly correlated to RPMs and load?

Could there be something wrong with the valvetrain that would cause it to give good compression numbers but open up an exhaust valve... too early? Causing the farty noise.

The very first thing I would do is check the entire exhaust from front to back for leaks or areas where it might be touching. I've seen exhausts rattles turn into songs depending on where they were touching. Most of them are also RPM correlated as well.

Thanks - I will check that out when I have some free time.

Any update on this? Interested to know what you found.

I found nothing. The sound is still present, but not any worse. I'm thinking that it always made the noise because the first time I noticed it is the first time I had the top down with it... which is the only time it's noticeable.

I'm thinking it's just the result of a strait pipe exhaust with a resonator.

i didnt read any of this, but the fart noise sounds like combustion. i think you have a car.

/comments.