Ever since my motor swap I have been having this backfire problem while I am decellrating. My mods are below.

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

Oh heh, well i was going to say a rich condition, but i see it's on de-accel.

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Gutted cat
-!AIR
-Gutted Air Boxes

[This message has been edited by branz28 (edited May 15, 2001).]

bwaahahahaa, right, it's the rich mixture caused by decel through the idle circuits of a carb...lol

didio rich condition.
But to be fair.
1.rich condition.
2.vac leak.
3.plugged cat or muffler.
4. could go on and on but 4 seems my limit tonight.
SSC
doh i gotta read the full post scratch 1.

[This message has been edited by SUPER-SPORT-CHEVY (edited May 15, 2001).]

btt

Could be an exhaust leak, but I guess you would notice that.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER, NO CAT
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
3:73 Richmond Gears and 3" Hooker Aero Chamber
15.61@ 95.2mph G-Teched, need tranny work
"There is nothing more addicting than speed"

Are you still running the AIR system? There's two air 'switches' one to switch from the manifold to the cat when warmed up, and another to switch from the cat to atmosphere to keep it from backfiring during decel.

well, 8 out of every ten times it's a rich condition or timing advance issue, but that's not 9 out of every ten. maybe i could recount them. along with recounting how many posts you've put for this backfire on decel condition.

I took the air of f thinking that this was the problem but that did not help, What would I look into for the timming? thanks

my dough would be on timing

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Webmaster: www.IROC-Z.org

are you running computer advance or vacuum?

Computer, It has been set to 4 and it is now at 6.

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

can you list the items you've replaced? this might help some.

Ok he is my situation, i have a 1986 Z28 that was a lg4 305 auto car originally, I swapped in a stock gm 350 (new) and a 5 speed ( the 5 speed was behind the 305 for years with the auto chip (4062 FFA ) the car upon deceleration will pop though the exhaust, but if I give it a little gas it will clear right up( the 305 never did this) the only thing that I changed with this swap was the intake and a msd 6al. I had the carb rebuilt and I even tried another carb from jet performance ( I will never deal with these people again) I tried the exhaust with a cat and with out, I now have a 0ff road pipe in there.

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

The MSD 6AL, is that a type of distributor I take it, is it Non CC. If it is and you're running with a CC Q-Jet, you need to either get a CC distributor or a non cc carburetor. Whether this is causing the popping in the exhaust I am not sure, but something to look into.

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'86 IROC
T-TOPS, TINTED WINDOWS, BRAKE LIGHT BLACKOUTS
GM GOODWRENCH 350
EDELBROCK TES HEADERS
FLOWMASTER, NO CAT
EDELBROCK 600CFM CARB.
KN AIRFILTER
ACCEL HEI DISTRIBUTOR
160* Stat
2:73 GEARS
Rebuilt 700R4, with manual valve body
B&M Megashifter
Soon to be installed
3:73 Richmond Gears and 3" Hooker Aero Chamber
Corvette Servo & .500 boost valve
15.61@ 95.2mph G-Teched, 1-2 shift slippage
"There is nothing more addicting than speed"

well turning the ingion off and than back on will cause that too(with flame at night)LOL

btt

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86Z28, GM 350, Jet perf Q-jet & chip Dual snorkel air cleaner, Edelbrock performer intake, Edelbrock headers, Edelbrock cat-back, Off road pipe, MSD 6AL, Accel Super Coil, Taylor Spiro-pro wires, Rapid fire plugs, Jet fan switch, World class t-5, Hurst Short Throw Shifter, Ram Flywheel, Center force dual friction clutch,Aluminum drive shaft, BW disc rear 3.45's & a posi, PBR calipers, Earls braided brake lines, Polygrapite bushings all the way around, poly tranny mount & torque arm mount, Hotchkis lower control arms & panhard rod, Rancho limiter straps, KYB struts & shocks, Gm Wonderbar, Edelbrock strut tower brace, SSM sub frame connectors, Jamex lowering springs, Carbon metallic brake pads, Crossed drilled rotors, Mobil 1 Tranny fluid & motor oil, GM syntheic rear end oil, K&N, Grant stering wheel, 1,200 watt system, Jet Black Paint, 91 Z28 rims, 92 wing, Tinted windows.

btt

two votes for exhaust leak.

Hmmm...I took out my AIR system from my car. But left the switches that your talking about. Should I atcually have taken them out? Will anything go wrong if I take them out? is anything going wrong cause I didnt?

Backfiring in the exhaust means there is unburned fuel in there and usually also some source of fresh air like an exhaust leak or something. Also can be a function of low spark lead/timing. My TPI car rumbles a bit on decel because i have backed off my timing even before it gets into DFCO. So unless i'm in an extreme decel it gives me the sound you are talking about. BTW, i programmed it this way on purpose. Unfortunately, there is no way for the DIYer to program chips for a CCCS car. The best you can do is swap in a vacuum advance dizzy, and run a tach signal into the reference signal to the ECM to trick it.
If you want to try to keep it in open loop to try to get rid of your 'problem' i think you'll find it just get worse since open loop for CCCS just means full rich ducty cycle on the MCS.

header leak...

Holly **** it took u since feb to get that fixed??

BLACK Z,
The #1 cause of backfire on decell is what in the old days is called the diverter valve and is now called the air management system. The air pump would be releasing air into the exhaust stream and ignighting the unburned fuel. So there is the key.. air - unburned fuel... But.. I just did the same deal,went to the 5.7 after my 5.0 and installed Edelbrock TES headers and when my car is cold It's little fatter to compensate for a cold engineand it pops everytime I shift.. Not unbarable or anything but it pops. and only when it's ice cold..
I see you have already taken some of the air pump stuff off,did
you just remove the hoses that go from the valveing to the one way valves on the manifolds and down to the cat ? if so the exhaust may be sucking air right through the one way valves on decell.. The exhaust will pull hard through there on decell. If not there is an extreme posibility that your just running to much fuel and the headers are lighting it off. The vacume is very high on decell too and it will pull fuel from the carb hard if there is any air volume through the throttle plates. Idle must be set low and the tps voltage set correctly. If it's a compter controlled carb them the 2 mixture adustments might be checked also..

BTW.. I am a California certified smog, electrical, drivability, A1-A4-A6-A8 and L1 ASE and all kindsa other stuff certified tech with about 30 years experiance.. Hope I have helped some...

90 Formula X - F engine... Mods...

* 355 C.I. -- 5 Speed -- WS6
* Ported & Polished Cylinder Heads Casting #993 as Recommended by Lingenfelters Book.
* 2.02 & 1.6 Manley Pro-Flo Valves
* G.M.P.P. Roller Cam Part # 14097395
* Harland Sharp 1.6 REatio Roller Rockers
* Speed Pro/TRW 1.25 Dome Forged Pistons
* Clevette Brgs, Cast Crankshaft, HD Rods, High Pressure/Volume Oil pump assy
* Complete Lower Assy Balanced
* Ported and Gasket Matched Intake Plentum, Runners and Manifold
* 52MM Holley Throttle Body
* Custom Built Adjustable Fuel Pressure Regulator Set at 46ls ( 51 under Full Throttle )
* Edlebrock Chrome T.E.S. Headers -- 50 State legal --
* Twin High Flow 3" Cats, 3" Exhaust tubing Replicates the Original Factory Dual Exhaust
* Flowmaster Cat Back System