4agze playing up ??

[PSI055]

Hey all, I have noticed my gze is poping quite alot out the muffler on back off does this sound like it need's tuning? .
Cause all the others i have heard dont do it.

Cheers Luke

[BigWillieStyles]

Hey mate what sorta exhaust setup you got?

[fade-e]

the backfire on throttle release is usually excess fuel... this occurs as far as i am aware because when the throttle is closed and no air is in the system (or little air) compared to the fuel being fed...

is there an exhaust sensor set on the car? as it should help to reduce that occuring...

other options could be slightly out of timing or possible little fine tuning required for the ecu (if not stock)...

i could possibly be wrong but thats where i would start... im sure one of the 4AG guys can better answer you...

[chrisellis]

mine used to do this a fair amount, does it alot less often now with all the components in the engine bay earthed properly.

[clean82]

Your air/fuel sensor that screws into exhaust manifold may be the problem, giving incorrect air/fuel info to the ECU( not cheap to replace? )

After removing the resonator ( the big muffler thing after the cat) on my Ae82 4agze and running just a cat and 6" rear muffler with 2.5" piping i started to get the same back fire. The guys at neal bates automotive said the backfire or "pop" is happening because of the fact the resonator used to supress this "pop". Car was dynoed and correct air/fuel was being supplied but the "pop" continued( stock ECU ). If the "pop" still occurs then mybe a larger resonator or muffler should stop this "pop'

Personally I have grown to like my "popping" exhaust and it only really happens when changing gear at high rev's

PS my car has 102 Db at 4grand and 108 Db when backing off sounds tuff, but a defect can't be too far away???

[PSI055]

Your air/fuel sensor that screws into exhaust manifold may be the problem, giving incorrect air/fuel info to the ECU( not cheap to replace? )

My O2 sensor isnt hooked up at all ..would this be a good place to start ?

[mic*]

My O2 sensor isnt hooked up at all ..would this be a good place to start ?

ummm.... yeah

[120ymania]

Yes as others have said it is most likely over fuelling, so your 02 sensor is prolly a good idea to hook up but also as "clean82" said it can be due to a large cannon muffler and those sort of large mufflers.

But also at the same time there shouldn't be too much fuel entering your cylinders whilst backing off as the stock computer and also after market computers have a function known as "Overrun" which when you back off it cuts the injectors so no fuel is entering the cylinders.

Hope that helps

Aaron

[oldcorollas]

But also at the same time there shouldn't be too much fuel entering your cylinders whilst backing off as the stock computer and also after market computers have a function known as "Overrun" which when you back off it cuts the injectors so no fuel is entering the cylinders.
Aaron

and as such, when the ECU is in "overrun" mode, the O2 sensor is NOT being used....

O2 sensor is used on cruise and light throttle, not on decel (overrun and high vac calues are often leaner than stoich)

if you have an aftermarket ECU, then perhaps it needs to have it's tuning altered.
if you have a stock ECU.. what can you "tune" on it, apart from timing?

anyway, lack of O2 sensor should not affect the fuelling, unless you are going into some diagnostic mode to the error code...

perhaps, you should check everything is hooked up correctly, and hook up the O2 sensor to increase your fuel economy...

whatever you do...

PS my car has 102 Db at 4grand and 108 Db when backing off sounds tuff, but a defect can't be too far away???

don't be a tool and do this...
you'll sound like a fuckwit, be a defect magnet, and piss off your neighbours.. and there is NO justification for this....

[nb86]

check for exhaust leaks too, a leak close to the engine can introduce enough O2 to reburn te mixture, unburnt fuel will ignite and youll sound like neal bates' WRC celica on overrun. not a common problem but if there is enough fuel there this might be it.

[PSI055]

Thanks oldcorollas, i have an aftermarket ECU its not like a back fire well sort of but its not just one, its like an old carby feed engine like a gemini engine how they always pop and shound shit on back off...its hard to explain.
Shouldnt it be just like back off then mmmmmmmmmmmmmmmmm like one consistant noise, not like back off mm pop pop pop pop pop pop sorry not the best way to describe it i know but its hard too.

[mic*]

whatever you do...

Originally Posted by clean82
PS my car has 102 Db at 4grand and 108 Db when backing off sounds tuff, but a defect can't be too far away???

don't be a tool and do this...
you'll sound like a fuckwit, be a defect magnet, and piss off your neighbours.. and there is NO justification for this....

Ur a funny chap stu.

I second that notion.

[-GT-]

check for exhaust leaks too, a leak close to the engine can introduce enough O2 to reburn te mixture, unburnt fuel will ignite and youll sound like neal bates' WRC celica on overrun. not a common problem but if there is enough fuel there this might be it.

An exhaust leak would not draw oxygen into the exhaust, even at idle your engine is pumping gases out, so this higher pressure would force exhaust gases out the leak, NOT draw air in, especially at 3-4 grand and more... and it would be making a very loud, shit sound.

If its popping away on overrun its unburnt fuel igniting in your exhaust, there's plenty of heat still in the exhaust to get it to ignition temp.

If you don't have an oxy sensor and are running a standard ecu it can increase this popping; the ecu detects the sensor is out of normal range (ie not there at all) and as a precaution some will permantly richen the mixtures so its in a kind of safe mode. When i was waiting to get a new oxy sensor my car was definately popping more and louder without it.

But, you're running a microtech without an oxy sensor, so it's just running the fuel maps its been told to. Its running rich and needs a bit of fine tuning if you want to get rid of it. Its probably not hurting anything apart from your fuel economy, it think people run rotaries rich, esp on overrun to help keep them cool? Not sure where i picked that up from though so if someone could confirm?

Either way, if you want it to stop tell your tuner to check out the tuning in the circumstances where its happening.

[takai]

Yeah, it is common to run a bit richer on closed throttle to keep the cylinders cool. My race car was running 13:1 on idle and closed throttle, but settled back to about 14:1 on throttle.
Rotaries do this quite commonly, as the thought is that it keeps the apex seals "wet" and a bit cooler. It is also one way of setting up antilag, albeit fairly bodgily.

[oldcorollas]

Thanks oldcorollas, i have an aftermarket ECU its not like a back fire well sort of but its not just one, its like an old carby feed engine like a gemini engine how they always pop and shound shit on back off...its hard to explain.
Shouldnt it be just like back off then mmmmmmmmmmmmmmmmm like one consistant noise, not like back off mm pop pop pop pop pop pop sorry not the best way to describe it i know but its hard too.

i know exactly what you mean...
in that case.. check what vac you are getting to when you go into decel.. lean that area out until the popping stops... BUT then check that when you apply throttle again, it is not jerky... i had to richen my lowest vfac point by a percent or two to find a balance between popping and hesiststing/bucking when throttle was applied again.....
you can cover this up with accel enrich, but it's better to get the high vac tune closer to start, and use minimal accel enrich (unless you can tune accel enrich based on rpm and MAP too?)