backfire(sound) help...

[maik21]

why my car backfire(sound, explosion) when i desacelerate (put off the gas pedal) .... it only backfire when y desacelerate, but when i acelerate or press the gas pedal, its seem to be fine. help please..i have new spark, spark plugs . the sparks are calibrated at 0.039 .

[paul devane]

ceeck gaskets along exhaust, especially if its aftermarket. also the nuts/bolts holding exhaust to turbo.whats air-filter like?:thinker

[navysnail]

how about timing?

[maik21]

its 15° btdc

[navysnail]

try running high octane, see if that fixes it.

[gyfer]

he only backfire when decelerate ...engine is running lean when you decelerate, high octane won't help...

check your injector, it might be leaking ( causing rich, thus backfire...)

you sure the "explosion" came from exhaust manifold/exhaust pipe, and not your engine... right ?(you are decelerating.. so it shouldn't be from engine anyway)

dirty valve, which cause the exhaust valve not closing tight can cause the problem too.. what's your compression check ?

[maik21]

240kid <--- i was running a 89 octane... and i am running now a 93 octane. but the problem still .

gyfer <--- the plug of inyector are good.theyre not leaking. because i dont have a new plugs.. i put an oem plugs. theyre fine.the explosion came from exhaust. it sound like a old(not fine) car.i dont know about compresion. but .. what you advice me? check the valve? adjust? 6 months ago, a mechanical adjust the rpms screw. and the air ratio screw, manifold intake. ... theres a question..if the butterfly is too close, will it cause explosion? i say that i have to readjust the screws to get the exacts rpms at idle, and adjust the tps to .45v .... what advice you to me? ..

im sorry for my english.. i am learn it. =) thanks for help.

[gyfer]

what butterfly ? throttle body ?your idle speed is adjust from Idle Air Adjusting Unit. aka I.A.Anot butterfly or throttle body. But there is a screw on intake side, near firewall then you can try to adjust your idle

maybe the old (oem) plug is leaking ?

compression check will ensure you engine is good, thus you valve is ok.

compression check recommended.check engine ignition timing too.how about air filter ?if all failed, check your fuel pressure regulator.

[maik21]

butterfly = throttle body. =) gyfergyfer <--- the air filter is new... the ignition timing i am sure that its fine.. but i check it.i dont check the fuel pressure regulator.. i check it. i never check it.a worse timing chain will produce backfire?

[gyfer]

a lose timing chain will cause problem... but I don't think you car will start if you have that problem...

if all failed, try a different MAF.

check your fuel injector again, maybe is failing....

[maik21]

i remove the aiv 4 months ago.. will it produce the problem?my car is a 240sx 90s 2.4l 12 valve

[navysnail]

no, i dont think aiv has anything to do with it unless you have a clogged cat

[maik21]

my car dont have cat. it was removed, and replace with a pipe. i have a flowmaster instaled.

the throttle body was closed. and i adjust the screw of the throttle body 3 times clockside. and adjust the airfuel ratio screw. and adjust my tps to .45 volts and my car down sound explode. ....before adjust... the sound is strong....after adjust.. the sound is weak... it sound a little....need it a readjust(more adjuts)?

[Neejay]

Taking a shot here, but Im gonna assume that the "test pipe" that replaced the cat is the problem. Its making you run rich...

[maik21]

Neejay <--- if the test pipe is the problem.. what advice you to me? i know that there are a diferents test pipe. (size).... my test pipe is small.. if i put a large test pipe, resolve it the problem ?

[maik21]

neejay <-- if i dont want to put a cat, what can i put as a cat? what kinda of pipe will replace a cat?

[gyfer]

If test pipe is equal diameter to your exhaust pipe diameter or bigger, it shouldn't be a problem, or cause a problem.

The potential problem for not having a CAT is sound polution, CO2 and others gas polution, and higher changes of getting a ticket. Getting a high flow cat can reduce the problem, good for environment, and less noisy exhaust too. I have a full 3inch exhaust, with larger than 4 inches CAT, and 3inch in and out straigh thru muffler. All mandrel bent so, i got to have the CAT.

I didn't know our TPS is adjustable, nor 240 has air/fuel ratio screw. I just know we have idle speed screw.

[nnkfws333]

haha we all backfire....you should hear the backfires on most of the SR's some can get pretty loud...scares the hell out of people next to me with there windows down.

[240_2NRman]

try running high octane, see if that fixes it.

high octain will only help if your car is detonating. other than that i had the same problem, its your fuel injectors they are either leaking or have a bad spray pattern VERY common with 240's also is your exhaust kinda popping when its at idle? cause if it is then its something in the exhaust to but im 99.5% sure its your injectors

[maik21]

240_2NRman--->when i go to the mechanic for a inyection service... the inyectors are cleaned with liquid(combustible) at high presion.. the explosions are more little.. it resolve the problem for 3 weeks.. but at 4 week.. the problem born again. gyfer--->there is a screw in the throttle body... and more back there is an other screw(fine adjust) (ka24e 12 valve).

[chmercer]

on this same subject - When i let my car get to low rpms, like 700-1k range, it will make a very quiet backfire noises. not like the KAPOP big backfire noise but a whole lot of small puffs. Does not do this on my stock exhaust. I am running 3" downpipe + catback with the stock guttet cat pipe. I always thought this sound was normal, just because usually the cat and resonator and larger muffler would stop the sound, but not if it is straight?

[MikeMurphy]

Im putting in 370cc injectors over the summer for a pre-turbo setup and I will let you know if it changes anything. I really think the nissan ECUs were just out of wack for putting in too much fuel upon deceleration. Maybe they didnt figure in the additional vaccuum on the injectors and thus they inject too much.

I set off car alarms with my S14

I would venture to say you dont hear it on the stock exhaust because it muffles it well. Doesent mean its not there though.

[chmercer]

you know what im talking about though? if other peoples cars do the same thing than im not worried about it

[USCS14DUDE]

Its a lack of back pressure in you exhaust system, i have header and cat back exhaust and mine pops, nothing to worry about.

[MikeMurphy]

chmercer,

Mine pops a bit upon deceleration at around 1800rpms

Its a lack of back pressure in you exhaust system, i have header and cat back exhaust and mine pops, nothing to worry about.

Explain to me how a lack of back pressure in the exhaust causes extra fuel to be injected and unburnt fuel to ignite making the sound?

I always thought the poping was only audible with a large exhaust, and with a smaller exhast not quite noticable. Just because its not noticeable, does not mean its not happening. Hopefully you can clear up my confusion.

[gyfer]

Explain to me how a lack of back pressure in the exhaust causes extra fuel to be injected and unburnt fuel to ignite making the sound?

obviously it can't

I won't want any back pressure on my car:D

[maik21]

hey .. when i buy my car.. it has the stock exhaust and the backfire was a little sound(0-10 <--- the sound was 1 some times was 2 )... and when i remove the stock exhaust and put a flowmaster... the sound was scale 8 ... sometimes 10. its very loud.... its happend when i decelerate at about 1000 rpms... im from mexico and the cat its very expensive to me. i dont have much money to buy a cat.. what can i buy to resolve it? should i put the stock muffler to my car? i have the stock muffler in the garden =).. i check the terminals(injectors for leaking) and its all fine. there are no leaking .

[MikeMurphy]

I really dont know man, but I cant see how a cat can help that much. Maybe im wrong but I just dont see it. I would suggest maybe checking on your coolant temp. sensor as if that is malfunctioning it could cause a bit of extra fuel to go into the cambers of doom. I hear that the specific sensor is prone to malfunction. I understand it can be read from the OBD port.

Im looking forward to soemone figuring this out. Seems to be applicable to quite a few 240s out there.

[maik21]

thanks MikeMurphy =)

[BuLLeTdrift]

if all this "backfire" sound is coming out of the exhuast, yes its from an exhuast w/o the cat. my friends did the same thing, but he liked it for some reason. if you drive up to a high RPM and let go of the gas and don't put in the clutch, you're gonna hear that "pop" in the exhuast. next time when you first start to decelarate, put the clutch in as fast as you can. you shouldn't hear ne thing, if you do, then i'd be worried.

if you guyz already said this same thing, i'm sorry. i just didn't feel like reading the whole page (lazy). i wanted to actually put in some info. on something i know.