exhaust backfire-whats the cause?
05-04-2010, 12:23 AM
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exhaust backfire-whats the cause? so my buddy has an ls1 camaro. everything runs smooth except for an occasional backfire from the exhaust. what can cause this?
05-04-2010, 01:02 AM
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Well, i know that the AIR system can cause backfires when completely letting off the gas after mild acceleration. Does this happen for long periods of time, or only during the first 5-10 minutes that the car is on?
05-04-2010, 02:41 PM
#5
might be running rich.
i had a little backfire when going WOT then suddenly letting off after my exhaust was opened up a little. leaned it out just a bit and the popping went away and (felt like) it pulled better up top. i tuned with with hptuners and a wideband.
i had a little backfire when going WOT then suddenly letting off after my exhaust was opened up a little. leaned it out just a bit and the popping went away and (felt like) it pulled better up top. i tuned with with hptuners and a wideband.
05-04-2010, 04:17 PM
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Check AIR and EGR if they have been deleted then like alot if people you will have backfire when letting off during WOT... If he has not been properly tuned (not saying that if you pop after tune it's not done right) he will be running rich VERY RICH.. I would beleive a good tune could lean him out a bit and get him back to that 16mpg+ in his car! Personal expeirience mine still pops but I am off the charts running rich.
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03-06-2016, 08:40 AM
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I road race a 2000 z28 with ls1. Stock tune, stock manifold with cats removed. Run o2 sensor simulators. Motor is restricted to 260 hp. Backfires after WOT with no load or after long straightaway. Any ideas of cause? Thanks.
03-06-2016, 05:49 PM
#10
Technically it's an "after-fire", but that's splitting hairs, because most people refer to it as a backfire (incorrectly. Technically.)
Like everyone's saying, both my LT1 Camaro and my LS1 TransAm pop after a 50%-100% throttle acceleration and then letting off the gas. I think it just has to do with the stock cam profile and AIR vs. exhaust process?
Like everyone's saying, both my LT1 Camaro and my LS1 TransAm pop after a 50%-100% throttle acceleration and then letting off the gas. I think it just has to do with the stock cam profile and AIR vs. exhaust process?
03-06-2016, 08:29 PM
#11
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The backfire after a WOT run is probably unburnt fuel hitting the very hot exhaust, your car is probably running a little rich.
03-08-2016, 09:59 AM
#12
I think that was the case for my LT1 Camaro, but my TransAm will do it moments after starting cold.
03-08-2016, 12:01 PM
#13
for a normal, stock, unmodified, engine that runs normal and well 99% of the time,
when you are at mid to high rpm's under a mid to high load then your air-fuel ratio will be towards the rich side from 13.5:1 to 12.5:1. and timing advance will be somewhere between 20° to 30° depending on rpm. when you let off the gas fast under that kind of condition, the throttle body slams shut and an immediate stoppage of air in to the cylinders happens.
normally the engine computer senses this and reduces fueling and maxes ignition timing up to and above 40° to maintain a running engine and not over fuel and not increase emissions but it's not exact
it is common for there to be a little popping or backfire in the exhaust for 1-2 seconds until combustion stabilizes and goes normal again. it's a result of incomplete combustion between a snap transition of higher rpm heavily load heavy fuel and ignition timing happening between 20-30° which may not be far enough in time from the exhaust valve opening and heat -- to -- low rpm no load, and the fuel injectors not reacting quickly to reduce fuel to that new condition. with that lower rpm comes reduced timing below 20° closer to when exhaust valve opens, if this happens too quick the result is combustion continues to happen when the exhaust valve opens causing noise, and/or incomplete combustion making it's way into the hot exhaust manifold where it finishes combusting making noise. this is normal and should only last 1 second and be minimal popping. if it always happens and easily happens, and the popping happens for 2-4 seconds then you are not managing fuel and ignition timing properly to handle that quick transition from high air flow to low air flow in & out of the engine. it happens more on motors & motorcylces with old mechanical ignitions that are fixed on rpm, where low rpm of 1500 or less means 10° timing always... unless a computer where it can be programmed based on the condition an input from sensors like map, maf, tps, and so on.
when you are at mid to high rpm's under a mid to high load then your air-fuel ratio will be towards the rich side from 13.5:1 to 12.5:1. and timing advance will be somewhere between 20° to 30° depending on rpm. when you let off the gas fast under that kind of condition, the throttle body slams shut and an immediate stoppage of air in to the cylinders happens.
normally the engine computer senses this and reduces fueling and maxes ignition timing up to and above 40° to maintain a running engine and not over fuel and not increase emissions but it's not exact
it is common for there to be a little popping or backfire in the exhaust for 1-2 seconds until combustion stabilizes and goes normal again. it's a result of incomplete combustion between a snap transition of higher rpm heavily load heavy fuel and ignition timing happening between 20-30° which may not be far enough in time from the exhaust valve opening and heat -- to -- low rpm no load, and the fuel injectors not reacting quickly to reduce fuel to that new condition. with that lower rpm comes reduced timing below 20° closer to when exhaust valve opens, if this happens too quick the result is combustion continues to happen when the exhaust valve opens causing noise, and/or incomplete combustion making it's way into the hot exhaust manifold where it finishes combusting making noise. this is normal and should only last 1 second and be minimal popping. if it always happens and easily happens, and the popping happens for 2-4 seconds then you are not managing fuel and ignition timing properly to handle that quick transition from high air flow to low air flow in & out of the engine. it happens more on motors & motorcylces with old mechanical ignitions that are fixed on rpm, where low rpm of 1500 or less means 10° timing always... unless a computer where it can be programmed based on the condition an input from sensors like map, maf, tps, and so on.
