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Just wondering if a bad cat can cause little popping noises....almost like a small backfire?My cat in the midpipe is going bad it's making all sorts of racket.This only happens when I shift and even then not all the time.I've noticed just recently that my exhaust seems much louder under the car...maybe a hole?Could that cause it?I'm not worried about the exhaust,because I'm putting on my turbo back soon,but want to make sure it's not something more serious.thanks

I'm unsure of the exact reason fo rthis noise, but i can get it in my automatic when the revs start dropping at high rpm.

Both my cats were fine at the time.

MK

see mine doesn't do it if I let off the gas,only when I shift and mainly between 2800 and 4000 rpm under heavy boost.Like unburned fuel exploding in the pipes.Won't do it at the same rpm's if I'm not on the throttle hard.

You let off the gas when you shift right (i'm assuming 5mt)


I do know exactly what noise you're talking about, just not sure of the cause.

MK

Most likely unburnt gas being combusted in the catalytic converter.

Do you have a MBC?

mk750 wrote:You let off the gas when you shift right (i'm assuming 5mt)


I do know exactly what noise you're talking about, just not sure of the cause.

MK

mk750-Yes, I thought you meant more of a compression issue sorry.

josh-no I'm at stock boost,I just mean when I'm on the throttle hard and turbo is spooled up then shift suddenly..popittypoppop...but like I said it is not constent and it started happening when my cat started to crap out.I'm happy if its just an exhaust issue because hopefully within two weeks I'll have my new turbo back exhaust put on

Well I have my new exhaust on and it's still happening. I've had this car for about 6 years and it never back fired before a couple of months ago. Like a said before it's not a loud back fire just a mellow pop. Could I have a cylinder thats running rich or maybe a foul plug? It's starting to worry me slightly. Any ideas of what to check or anything? Oh ya no CEL's ever,except when my alternator took a crap. Thanks

Have you reset the ECU? Let it learn the new exhaust and see if the problem will magically go away.

Have you guys ever heard what it sounds like when the blow off valve isnt function correctly, so the air crashes into the throttle plate and back into the turbo? Maybe thats this problem.

Brat4by4 wrote:Have you reset the ECU? Let it learn the new exhaust and see if the problem will magically go away.

No I haven't, I was wondering if I should actually. I also just put in a k&n air filter about 3 days before exhaust install. This was happening for a couple months with the stock exhaust too. In terms of what ciper suggested, maybe, I can't really hear the recirc. valve when shifting but it's hard to hear anyways isn't it?

Another thing about what ciper suggested, It does seem like the popping sound comes from the front of the car sometimes. It doesn't always happen(it's kinda random so it suprises me) but at one point today when it happened I thought it came from the engine bay.

Pulled the codes today before resetting the ecu and I got 3. 23-airflow sensor..24-air control valve...49-airflow sensor. I tried resetting the ecu every way I know how,about 4 different ways, and the codes are still present. Could one of these errors cause the popping? After resetting the ecu the first time I went for a spirited drive and it did happened once again.

It's my o2 sensor. Checked today and it is bad. This is causing me to run real rich. So it's unburnt gas igniting in the cat. Thanks for the ideas

You never got a CEL for the 02 sensor?

Sure didn't, strange I know. I got a code 32 when doing a D-mode check, thats was prompted me to check the wiring and sensor. I don't get a code for it when I do a read memory mode check either, which is strange. I can't reset my ecu either. I guess I have to fix the problem first.

If you get popping when you let off the gas, it's usually an issue with Fuel Pressure Regulator. Either the vaccum line to it has a leak or otherwise. This is because FPR's are designed to cut fuel when off-throttle.

But you're saying that this is not what happens, so I'm useless to you.