Ok so I'm on my way home from work about 1/2 hour ago with the stereo turned up and I feel my car sorta shaky when im about to stop, so i pause the stereo and i hear a small pop coming from under the car every now then.. when im moving slow the car sorta feels a tad rough.. sofar its the first time this happened but I was wondering what this could be.. I just had a tuneup about 2000 miles ago.. timing is a possibilty im assuming? thanks for any help in advance..

Frank

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1991 Camaro Z28
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CURRENT MODS:
350 TPI, Automatic, Edelbrock Headers, Edelbrock Runners, Flowmaster Exhaust, MSD 8.5mm wires, Autolite Double Platinum Plugs, MSD Cap/Rotar, Random Technology high flow cat, Hypertech Power Chip (160 Deg Thermo), K&N Filterchargers
STEREO MODS:
Pioneer DEH-P6000, 2 JL Audio 12W3 subwoofers in custom hatch enclosure,
Rockford 250a2 Amp, Infinity Kappa 4x6" plates & 6x9's
WEBMASTER: Frank's Thirdgen F-body Website(eventually)

 

ttt

 

Slayer,

My first guess would be ignition, but if the car runs normally under moderate cruise and acceleration, that might not be the case. I would then look at running hot and/or lean. The high temps created by lean burning and an inoperative EGR would heat the chambers enough to cause detonation, spark retard, and afterfire in the exhaust/cat converteron deceleration, when there isn't adequate intake air to burn the fuel completely. Where to start is a guess. Fuel pressure, oxygen sensor, AIR diverter, EGR system, and base timing are all good things to measure and inspect. Testing the EGR can be a littel difficult on a TPI, so eliminate the others first. A "lazy" TPS might also cause a problem, so make sure the voltage at idle is correct and there are no lags or dead spots in the TPS output.

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Later,
Vader
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"Let the bodies hit the floor!"
Adobe Acrobat Reader

 

I had a similar problem when I had an exhaust leak at my y-pipe where it met my passenger side header, when slowing down the exhaust would have a popping sound like a backfire, but this only occured when deaccelerating.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
Exhaust Cut-Out
"There is nothing more addicting than speed"

 

If you noticed it since your last tune-up, re-check your timing. I had a similar problem after I re-installed my distributor. I marked the cap and lined it up the way it was supposed to go, but noticed the same problem you were referring to. When I checked the timing with a timing-light, it was way retarded.

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92 Camaro RS, LO3, 5-spd, T-tops

Performance:
K&N Open Air Filter, Edelbrock performer TBI intake, Fastchip Prom, Timing +4 degrees, Centerforce clutch, Xact 8mm wires, SLP 1 3/4" Headers (coated), Flowmaster Catback Exhaust, Z28 Grille w/aftmkt fog lamps, MacEwen white-face guages
Electronics:
Alpine 8030 Alarm System, Valentine One Radar Detector (How did I ever drive without one?), Pioneer DEH 7450 Head Unit w/6-pack CD changer, Pioneer DEQ 7600 Sound Processor, 2 Kenwood KAC-846 Amps powering 2 12" Pro Red subs, 2 Pioneer 6x9 and 2 MTX 4x6 speakers.
NEXT UP: TBI mods, 3.42 gears w/Torsen posi

 

A-I-R.

It doesn't take much of a y-pipe, header, collector or other exhaust gasket leak to get a pop when you let off the gas.

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1992 Pontiac Firebird 350/Six Speed
1987 Toyota Pickup 383/500+ HP

 

My exhaust pops when I'm going decellerating downhill. Is it normal?

 

If your car idles rough and pops in the exhaust, most likely you need spark plugs... one cylinder is misfiring, dumping raw unburned fuel into the exhaust.

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"So many Mustangs, so little time..."
ICON Motorsports

 

hey mark, I had the same problem actually a month or so ago, there was a gasket or something in between the header and y-pipe that was either ruined or missing and i had that exhaust leak for a while, but I had that fixed already.. as for new spark plugs they were changed at the tuneup a couple thosuand miles ago, can't imainge they are no good already.. but they car does idle rough and it shakes if i let off the brake.. kinda like stop and go, but not really bad just noticeably..

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1991 Camaro Z28
------------------
CURRENT MODS:
350 TPI, Automatic, Edelbrock Headers, Edelbrock Runners, Flowmaster Exhaust, MSD 8.5mm wires, Autolite Double Platinum Plugs, MSD Cap/Rotar, Random Technology high flow cat, Hypertech Power Chip (160 Deg Thermo), K&N Filterchargers
STEREO MODS:
Pioneer DEH-P6000, 2 JL Audio 12W3 subwoofers in custom hatch enclosure,
Rockford 250a2 Amp, Infinity Kappa 4x6" plates & 6x9's
WEBMASTER: Frank's Thirdgen F-body Website(eventually)

 

Only thing that is for sure is that you've got unburnt fuel in the exhaust!