When the car is engine braking i get allot of gurgle and pop. Ive also noticed that the exhaust seems to smoke for about 20-30 seconds after i turn the car off. Any ideas? Running rich?

2/23/2010 9:34:22 AM

Is your exhaust system aftermarket? Just about every car's engine will gurgle and pop when you let off the throttle (in gear). It's natural and is just excess fuel combusting in the exhaust system. On a stock exhaust system you usually can't hear it due to sound muffling.

Does the exhaust smoke for 20-30 seconds all the time? Or maybe just in cold and/or humid weather? It might be running a bit rich. Of course if its anything noticeable you should be able to tell from your fuel mileage.

What car is this for?

2/23/2010 9:41:26 AM

its a GTO,

LS2, has headers, and a catback.

It here is the dyno.






[Edited on February 23, 2010 at 9:57 AM. Reason : As a side note i havent been getting great fuel mileage, probably 3mpg lower than most with my car.]

2/23/2010 9:55:16 AM

LOL. Yeah, that car should be crackle and popping stock anyway, lol.

Since having the cat back and headers installed have you had it tuned? I know you posted your dyno sheet, but when you were there did you just do a few runs or did you have it tuned as well?

2/23/2010 10:01:03 AM

No it was dyno tuned (by RPM in cary)

I could take it back, it was actually tuned by the guy i got it from back in may.

2/23/2010 10:30:57 AM

Quote :

"As a side note i havent been getting great fuel mileage, probably 3mpg lower than most with my car."

3mpg lower than most with a stock car or 3mpg lower than most with similar mods? That might just be the price you pay for the extra 30 HP and 30 lb ft of torque that they picked up over the 9 dyno runs they made during tuning.

The smoke doesn't sound good though. Does it smoke while running too?

[Edited on February 23, 2010 at 10:36 AM. Reason : l]

2/23/2010 10:36:15 AM

2/23/2010 10:52:56 AM

wrap a dryer sheet over the exhaust outlet using a rubber band, tip tie, etc. for 10 minutes or so. if you have a black circle on it the car is running rich.

do you happen to have the a/f graph from the dyno printout?

[Edited on February 23, 2010 at 10:55 AM. Reason : -]

2/23/2010 10:54:32 AM

Equally important question...What color is the smoke?

2/23/2010 11:38:13 AM

Isnt the A/F on the graph.

Im getting around 16mpg, with a lot of highway driving, alot are getting aroudn 18 with similiar mods.

its not burning oil, or at least when i have checked it.

2/23/2010 11:47:05 AM

shouldn't be any gas entering the combustion chamber during engine braking. my civic does this a little bit because the engine braking vacuum threshold is a little mis adjusted. maybe you have a leaky fuel injector?

2/23/2010 11:52:21 AM

you are running rich at higher rpm. You are actually loosing power and gas mileage because of it.

2/23/2010 11:52:35 AM

Quote :

"When the car is engine braking"

2/23/2010 12:33:17 PM

gassers dont engine brake.

2/23/2010 1:00:58 PM

yeah they do. just not well

2/23/2010 1:02:39 PM

hmm i didnt know that. i thought it was all transmission.


The more you know

2/23/2010 1:28:47 PM

If you're in gear and not using the throttle the mechanical drag slows down the car.

[Edited on February 23, 2010 at 2:17 PM. Reason : k]

2/23/2010 2:16:51 PM

more gurgle and pop than usual = exhaust leak

smoking 20-30 seconds after shutoff = wtf??

2/23/2010 2:23:20 PM

Ill see if i can get a video.

Yea, im pretty sure i got an exhaust leak, ive had everything welded except headers to the cats...im afriad to weld that because i dont want to have to get them cut if i do any work. Is there some kinda leak proof flange that i could get welded on? Right now they are slip fit.

2/23/2010 2:36:12 PM

I guess an exuast leak would make sense, might even effect gas milage. I know at one point i looked up some kinda leak proof exhaust flange that they could weld on.

Looked kinda like a ball and socket joint?

Would something like this work

http://www.hedman.com/products/?id=3469&iset=3716&rsku=

i think its 3 inch to 3 inch.

Or, pull out the current cats and put in these

http://cgi.ebay.com/ebaymotors/3-Catalytic-Converter-High-Flow-Stainless-Steel_W0QQitemZ200442715061QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item2eab511bb5#ht_1697wt_1165

Should give it some proformance.


[Edited on February 23, 2010 at 3:02 PM. Reason : dd]

2/23/2010 2:48:21 PM

were the headers just put on?


how many tanks of fuel have you gone through since the dyno runs? is this the same tank from when the car was on the dyno?

2/23/2010 4:29:16 PM

jesus fucking christ this forum has gone backwards

Quote :

"Should give it some proformance."

2/23/2010 4:59:41 PM

No headers have been on since may of 09, i purhcaed the car with a bunch of mods done to it already.

When i got it it had some exhaust leaks(or developed them), possilby due to me jamming the exhaust with a speed bump.

I had most of the system welded, except for the joint between the headers and the factory mid pipes.

I believe its still leaking there, the factory catted midpipes are fairly restrictive.

I would think it might be better to just get the factory catted midpipes replaced with a flange connection and a high flow cat (have the shop put some piping together.

Would this be practical?

2/23/2010 5:04:01 PM

Practical??

2/23/2010 6:04:42 PM

omg.

:carlface:

2/23/2010 7:01:30 PM

http://www.summitracing.com/parts/JEX-FLX3010B/?rtype=10

[Edited on March 4, 2010 at 8:25 PM. Reason : -]

2/23/2010 7:33:42 PM

Quote :

"Or, pull out the current cats and put in these http://cgi.ebay.com/ebaymotors/3-Catalytic-Converter-High-Flow-Stainless-Steel_W0QQitemZ200442715061QQcmdZViewItemQQptZMotors_Car_Truck_Parts_Accessories?hash=item2eab511bb5#ht_1697wt_1165 Should give it some proformance. PERFORMANCE "

Okay. First of all, that's a generic product on ebay, if I'm not mistaken. They say "High Performance Cat" Really? You're just going to take their word for it? They don't even post the CFM, which stands for Cubic Feet per Minute. This is the flow rate of the cat. The higher the number, the more "performance" you'll get out of it. That could be just a generic 200 CFM "high flow cat" for all you know. That's like a guy saying, "Hey, I've got a large penis." Large compared to what? A chimpanzee? You need to get data/measurements to get a more accurate description of what's really being described here... 400 is a pretty good number. I've seen a few 500CFM cats... If you engine is putting out more than 400-500CFM, then you need to be running dual cats to take advantage of the maximum PERFORMANCE gain.

Here's an interesting website. They claim to have a >600+ CFM 3" inlet/outlet Cat. I don't know them, just something I discovered.

2/23/2010 7:49:36 PM

How about an interesting link?

2/23/2010 9:07:35 PM

lol wow. What a fail.

http://www.randomtechnology.com/

And for clarification, by dual cats, I mean you need two catalytic converters set up in parallel, not in series, to gain the additional benefit..

[Edited on February 23, 2010 at 9:22 PM. Reason : .]

2/23/2010 9:20:45 PM

Seems like quite a few guys on the gto board have been using the thunderbolt ebay models with success.

Yea i know they are crappy ebay parts, but they claim they work better than the stock ones (which neck down to 1.5 inches.

and of course their would be 2 of them, im trying to replace the current ones with something that flwos a little more, and also seal up the leaks

I think i know a place where i can get passed with longtubes, but I really dont want any more noise from the car

[Edited on February 24, 2010 at 12:47 AM. Reason : dd]

2/24/2010 12:44:56 AM

Okay,

I drug myself under the car and figured out a bit. Evidently the mid pipes are not stock and are already running a 3inch pipe with some cats on there.

My concerns are the slip fit at the collectors, as well as the far (passenger pipe) hanging low enough to drag on speed bumps.

Any suggestions on a shop to check.

Also, i seem to be getting pretty crappy mpg compared to other cars in the same class type of driving. Any way to check the O2 sensors?

Would it be a good idea to take it back to the tune shop to see if its running rich.












[Edited on March 1, 2010 at 10:11 PM. Reason : dd]

3/1/2010 10:01:24 PM

I think you can hear the leak from underneith

http://www.youtube.com/watch?v=8ZrFbiK3ov4

3/2/2010 7:02:56 AM

wait

is this with or without the electric supercharger installed?

3/3/2010 12:15:39 AM

Yeah, needs moar electric supercharger

3/3/2010 12:43:11 AM

It hasn't been suggested yet. check out your muffler bearings.

take the car to a exhaust shop. you obviously do not know what you are talking about at all.

3/3/2010 3:42:48 PM

The supercharger blew the pipes.

3/4/2010 2:15:31 PM

i'm telling ya, you need this or else you'll keep blowing gaskets.

http://www.summitracing.com/parts/JEX-FLX3010B/?rtype=10

[Edited on March 4, 2010 at 8:25 PM. Reason : -]

3/4/2010 8:00:33 PM

^ he speaks the truth. Don't ask how I know.

3/4/2010 8:14:08 PM

Have you checked the resonator fluid level. It might be low.

3/4/2010 11:17:56 PM

Went to RJ's

He took a look at it confirmed leak. Said he can fix the leak but the problem is the midpipes are too low.

Told me to do it right i need to weld on flanges and then hell make some mid pipes to replace the crappy ones that hang low. $400

Sound reasonable?

3/24/2010 11:29:46 AM

R&j in apex? They do good work but are $texas

3/24/2010 12:09:07 PM

No the one on capital

3/24/2010 3:07:33 PM

The $400 I'm not going to comment on...but i will say that he has done top-notch work for me in the past

3/24/2010 7:24:32 PM

$400 sounds good to me

3/25/2010 2:52:33 AM

d i would ask, the guy seemed like a real straight shooter, and seemed to want to do it right.

3/25/2010 6:36:18 AM