Loud ass hissing noise

tweiss3 · 06-27-2011, 07:53 PM

91 Naturally Aspirated

Drove and sounded fine on the way to work this morning and at lunch. On the way home however, I hear a loud ass hissing noise (can't figure where, tried for about an hour). I also have no power. It still feels smooth, just no fucking power.

I have the factory emissions in place. Any ideas?

Dzire · 06-27-2011, 08:25 PM

might be a bad vacuum leak somewhere

tweiss3 · 06-27-2011, 08:38 PM

where would i look for the vac leak? It does sound like one, but idles fine.

Pete_89T2 · 06-27-2011, 08:51 PM

A vacuum leak big enough to be heard would result in a crappy idle. Where in the band is the car lacking in power - top end or everywhere? Did the S5 NAs use pressure from the air pump to operate aux ports/VDI; maybe the hiss is from an air pump plumbing leak?

tweiss3 · 06-27-2011, 08:56 PM

It may be airpump. I do believe it was used for aux port operation. I'll see if i can figure out where it could come from and check it tomorrow

tyler · 06-27-2011, 08:59 PM

Can it be heard while reving in neutral?

tweiss3 · 06-28-2011, 05:30 AM

yes

tyler · 06-28-2011, 07:44 PM

Is this noise heard at all times or under load?

tweiss3 · 06-28-2011, 08:14 PM

yes, its there all the time

tweiss3 · 07-01-2011, 05:39 PM

It appears to be coming from the header to downpipe connection? Could my cat have melted and blocked cause it feels like anything above 3k is where the lag is. I may try to pull it tomorrow morning and see if it looks free and clear.

I tested all the variable intake valves and went over all pressure and vacuum hoses, and they all worked and were in good condition.

NoDOHC · 07-01-2011, 10:04 PM

Melted cat is a good possibility, the best theory I have heard so far.

tweiss3 · 07-02-2011, 03:55 PM

It was the cat, i got pictures to post later. I gutted it and put it back in, im up and running again like ot should be

tweiss3 · 07-05-2011, 06:37 PM

pulled the cat and saw it wasn't being a good girl

so i punished it

tyler · 07-05-2011, 09:37 PM

Haha nice...I almost gutted my cat but I don't wana buy another for echeck

NoDOHC · 07-05-2011, 11:21 PM

Yeah, I have seen the plugged cat before (several times) unfortunately, I had to replace it (emissions). I think that the guts may have fallen out lately though, as I noticed the car being a little louder. If I don't look, then I don't know....

Glad you found the issue!

06-27-2011, 07:53 PM	#1
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	Loud ass hissing noise 91 Naturally Aspirated Drove and sounded fine on the way to work this morning and at lunch. On the way home however, I hear a loud ass hissing noise (can't figure where, tried for about an hour). I also have no power. It still feels smooth, just no fucking power. I have the factory emissions in place. Any ideas? __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

06-27-2011, 08:25 PM	#2
Dzire Rotary Fanatic Join Date: Apr 2008 Location: B,ham AL/Hollywood FL Posts: 151 Rep Power: 18	might be a bad vacuum leak somewhere __________________ RX8 2004 GT RX7 1988 TII

06-27-2011, 08:38 PM	#3
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	where would i look for the vac leak? It does sound like one, but idles fine. __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

06-27-2011, 08:56 PM	#5
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	It may be airpump. I do believe it was used for aux port operation. I'll see if i can figure out where it could come from and check it tomorrow __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

06-28-2011, 05:30 AM	#7
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	yes __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

06-27-2011, 08:51 PM	#4
Pete_89T2 Lifetime Rotorhead Join Date: Apr 2010 Location: Elkton, MD Posts: 874 Rep Power: 16	A vacuum leak big enough to be heard would result in a crappy idle. Where in the band is the car lacking in power - top end or everywhere? Did the S5 NAs use pressure from the air pump to operate aux ports/VDI; maybe the hiss is from an air pump plumbing leak?

06-27-2011, 08:59 PM	#6
tyler Rotary Fan in Training Join Date: Jun 2011 Posts: 64 Rep Power: 15	Can it be heard while reving in neutral?

06-28-2011, 07:44 PM	#8
tyler Rotary Fan in Training Join Date: Jun 2011 Posts: 64 Rep Power: 15	Is this noise heard at all times or under load?

06-28-2011, 08:14 PM	#9
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	yes, its there all the time __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

07-01-2011, 05:39 PM	#10
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	It appears to be coming from the header to downpipe connection? Could my cat have melted and blocked cause it feels like anything above 3k is where the lag is. I may try to pull it tomorrow morning and see if it looks free and clear. I tested all the variable intake valves and went over all pressure and vacuum hoses, and they all worked and were in good condition. __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

07-01-2011, 10:04 PM	#11
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 18	Melted cat is a good possibility, the best theory I have heard so far. __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)

07-02-2011, 03:55 PM	#12
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	It was the cat, i got pictures to post later. I gutted it and put it back in, im up and running again like ot should be __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

07-05-2011, 06:37 PM	#13
tweiss3 Mazda Lover Join Date: Aug 2010 Location: Akron, Ohio Posts: 319 Rep Power: 16	pulled the cat and saw it wasn't being a good girl so i punished it __________________ 2004 Mazda6 V6 5-spd - still waiting on money for a motor 1991 Mazda RX7 NA 5-spd - my new DD with 145,000 miles

07-05-2011, 09:37 PM	#14
tyler Rotary Fan in Training Join Date: Jun 2011 Posts: 64 Rep Power: 15	Haha nice...I almost gutted my cat but I don't wana buy another for echeck

07-05-2011, 11:21 PM	#15
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 18	Yeah, I have seen the plugged cat before (several times) unfortunately, I had to replace it (emissions). I think that the guts may have fallen out lately though, as I noticed the car being a little louder. If I don't look, then I don't know.... Glad you found the issue! __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic)