backfiring through exhaust after rebuild???

shelby2 · 02-15-2001, 05:32 PM

maybe someone here can help me. i just recently put my mustang back together and i have a problem. i have backfiring through my exhaust and i don't know why. it did not do any off this until i put my new heads, intake, tb/egr plate, maf, injectors, etc on. i have it timed right at 14 degrees and it idles at about 800 (sounds mean). i was just wondering if it could be because of bad sensors. the o2 sensors have lots of miles on them as well as the ect and act sensors. just wondering if anyone has had a similar problem. also, i have heard that c&l mass air sensors can cause some bad problems as well, but don't know about this. any ideas would be great and i appreciate anyone's replies.

------------------
shawn hill
1967 ford mustang coupe, red w/white stripes, hood scoop, front and rear spoiler, sefi and c4, trickflow intake, 70mm mac tb/egr, billet fpr, 24# inj, c&l maf, heavy duty c4 w/transgo shiftkit, flowtech longtubes w/turbo mufflers, t-rex inline pump, ported and polished E7TE heads w/1.94,1.60 valves, lunati 292 cam, harland sharp 1.6 rollers, conventional 8" with 2.79 gears (soon will be gone)

kenneth kimble · 02-15-2001, 08:46 PM

DUDE Re-check your plug wires,it sound like thay are cross!!!!
Been there, none that!

ken

------------------

Dark Knight · 02-16-2001, 03:47 PM

mine does it some too..but not real bad.. usually a small air leak into the exhaust does it..is it just one loud one or kinda burble? run fine otherwise? if it runs fine, you might loosen the H-pipe from the headers and re-tighten it.. cant hurt to change the 02 sensors while your down there either ;-)

------------------
84 convt,'95 302,AFR's, performer
3.55's, underdrives shorties
14.16@100.08
and a '68 stang that WAS nasty ;-)
MY ride

shelby2 · 02-16-2001, 04:44 PM

here's the thing, i have long tube headers with true dual exhaust so there is no h-pipe. it does not do it all the time and sounds as though it is coming from the drivers side pipe. it usually happens at low rpm's mostly at part throttle. maybe i'll take a look at the exhaust and i was going to get new sensors anyway.

this is what i thought the problem is. i thought that since the car has only 2.79 gears that the popping was from pre-ignition (detonation) because the power range for the car does not happen until about 3000 rpm and i thought that the computer would advance the timing so much that the engine couldn't keep up and therefore detonate, but i don't know. i am also going to have a custom chip made for it to change the fuel curve.

i hope it is what you think it is being the exhaust. i do know that where the header collector meets the exhaust pipe is not a real good fit. i have the aluminum exhaust gaskets that have a lot of wear on them and probably doesn't seal right. i'll have to check into that as well.

thanks Dark Knight

------------------
shawn hill
1967 ford mustang coupe, red w/white stripes, hood scoop, front and rear spoiler, sefi and c4, trickflow intake, 70mm mac tb/egr, billet fpr, 24# inj, c&l maf, heavy duty c4 w/transgo shiftkit, flowtech longtubes w/turbo mufflers, t-rex inline pump, ported and polished E7TE heads w/1.94,1.60 valves, lunati 292 cam, harland sharp 1.6 rollers, conventional 8" with 2.79 gears (soon will be gone)

Dark Knight · 02-16-2001, 08:12 PM

does the car run good otherwise? does it backfire when you let off the gas or just at random? 02 sensors could cause a rich backfire too.. excess fuel in the exhaust..

------------------
84 convt,'95 302,AFR's, performer
3.55's, underdrives shorties
14.16@100.08
and a '68 stang that WAS nasty ;-)
MY ride

shelby2 · 02-19-2001, 04:28 PM

actually, the car is running rough and sluggish in the low rpm's and i have the timing at 14 degrees. i was thinking of getting a msd box and coil to see if that would help me out. when i do advance the distributor past the 14 degree point the throttle response is smoother and the engine runs better, but the rpm's are to high so when i put it in gear the engines dies, and i have the throttle adjusted down as much as i can. i was going to get new o2 sensors but am waiting for a friend to see if he can get them for free.

it does not do it when i let off of the throtte, only when i am accelerating and ad that only once in a while. i am stumped. i have also noticed some pinging in the motor which i think may be advanced to far. i'll have to look into it more though. also, the backfiring seems to only be in the low rpm's. i was thinking that since my gears are so low that the computer's advancing is to far ahead of my combo's powerband which starts around 3000 rpm.

------------------
shawn hill
1967 ford mustang coupe, red w/white stripes, hood scoop, front and rear spoiler, sefi and c4, trickflow intake, 70mm mac tb/egr, billet fpr, 24# inj, c&l maf, heavy duty c4 w/transgo shiftkit, flowtech longtubes w/turbo mufflers, t-rex inline pump, ported and polished E7TE heads w/1.94,1.60 valves, lunati 292 cam, harland sharp 1.6 rollers, conventional 8" with 2.79 gears (soon will be gone)

02-15-2001, 05:32 PM	#1
shelby2 Registered Member Join Date: Nov 1999 Location: O Fallon, IL Posts: 87	backfiring through exhaust after rebuild??? maybe someone here can help me. i just recently put my mustang back together and i have a problem. i have backfiring through my exhaust and i don't know why. it did not do any off this until i put my new heads, intake, tb/egr plate, maf, injectors, etc on. i have it timed right at 14 degrees and it idles at about 800 (sounds mean). i was just wondering if it could be because of bad sensors. the o2 sensors have lots of miles on them as well as the ect and act sensors. just wondering if anyone has had a similar problem. also, i have heard that c&l mass air sensors can cause some bad problems as well, but don't know about this. any ideas would be great and i appreciate anyone's replies. ------------------ shawn hill 1967 ford mustang coupe, red w/white stripes, hood scoop, front and rear spoiler, sefi and c4, trickflow intake, 70mm mac tb/egr, billet fpr, 24# inj, c&l maf, heavy duty c4 w/transgo shiftkit, flowtech longtubes w/turbo mufflers, t-rex inline pump, ported and polished E7TE heads w/1.94,1.60 valves, lunati 292 cam, harland sharp 1.6 rollers, conventional 8" with 2.79 gears (soon will be gone)

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02-15-2001, 08:46 PM	#2
kenneth kimble Registered Member Join Date: Apr 1999 Location: chesapeake va. Posts: 89	DUDE Re-check your plug wires,it sound like thay are cross!!!! Been there, none that! ken ------------------

02-16-2001, 03:47 PM	#3
Dark Knight Registered Member Join Date: Oct 1998 Location: Az Posts: 854	mine does it some too..but not real bad.. usually a small air leak into the exhaust does it..is it just one loud one or kinda burble? run fine otherwise? if it runs fine, you might loosen the H-pipe from the headers and re-tighten it.. cant hurt to change the 02 sensors while your down there either ;-) ------------------ 84 convt,'95 302,AFR's, performer 3.55's, underdrives shorties 14.16@100.08 and a '68 stang that WAS nasty ;-) MY ride

02-16-2001, 04:44 PM	#4
shelby2 Registered Member Join Date: Nov 1999 Location: O Fallon, IL Posts: 87	here's the thing, i have long tube headers with true dual exhaust so there is no h-pipe. it does not do it all the time and sounds as though it is coming from the drivers side pipe. it usually happens at low rpm's mostly at part throttle. maybe i'll take a look at the exhaust and i was going to get new sensors anyway. this is what i thought the problem is. i thought that since the car has only 2.79 gears that the popping was from pre-ignition (detonation) because the power range for the car does not happen until about 3000 rpm and i thought that the computer would advance the timing so much that the engine couldn't keep up and therefore detonate, but i don't know. i am also going to have a custom chip made for it to change the fuel curve. i hope it is what you think it is being the exhaust. i do know that where the header collector meets the exhaust pipe is not a real good fit. i have the aluminum exhaust gaskets that have a lot of wear on them and probably doesn't seal right. i'll have to check into that as well. thanks Dark Knight ------------------ shawn hill 1967 ford mustang coupe, red w/white stripes, hood scoop, front and rear spoiler, sefi and c4, trickflow intake, 70mm mac tb/egr, billet fpr, 24# inj, c&l maf, heavy duty c4 w/transgo shiftkit, flowtech longtubes w/turbo mufflers, t-rex inline pump, ported and polished E7TE heads w/1.94,1.60 valves, lunati 292 cam, harland sharp 1.6 rollers, conventional 8" with 2.79 gears (soon will be gone)

02-16-2001, 08:12 PM	#5
Dark Knight Registered Member Join Date: Oct 1998 Location: Az Posts: 854	does the car run good otherwise? does it backfire when you let off the gas or just at random? 02 sensors could cause a rich backfire too.. excess fuel in the exhaust.. ------------------ 84 convt,'95 302,AFR's, performer 3.55's, underdrives shorties 14.16@100.08 and a '68 stang that WAS nasty ;-) MY ride

02-19-2001, 04:28 PM	#6
shelby2 Registered Member Join Date: Nov 1999 Location: O Fallon, IL Posts: 87	actually, the car is running rough and sluggish in the low rpm's and i have the timing at 14 degrees. i was thinking of getting a msd box and coil to see if that would help me out. when i do advance the distributor past the 14 degree point the throttle response is smoother and the engine runs better, but the rpm's are to high so when i put it in gear the engines dies, and i have the throttle adjusted down as much as i can. i was going to get new o2 sensors but am waiting for a friend to see if he can get them for free. it does not do it when i let off of the throtte, only when i am accelerating and ad that only once in a while. i am stumped. i have also noticed some pinging in the motor which i think may be advanced to far. i'll have to look into it more though. also, the backfiring seems to only be in the low rpm's. i was thinking that since my gears are so low that the computer's advancing is to far ahead of my combo's powerband which starts around 3000 rpm. ------------------ shawn hill 1967 ford mustang coupe, red w/white stripes, hood scoop, front and rear spoiler, sefi and c4, trickflow intake, 70mm mac tb/egr, billet fpr, 24# inj, c&l maf, heavy duty c4 w/transgo shiftkit, flowtech longtubes w/turbo mufflers, t-rex inline pump, ported and polished E7TE heads w/1.94,1.60 valves, lunati 292 cam, harland sharp 1.6 rollers, conventional 8" with 2.79 gears (soon will be gone)