Very bad cylinder misfire..

[salisch1]

Car is a 1992 240sx s13 with a KA24DE, just got done with transmission swap and everything was fine the first day now the second day and its backfiring a lot. It backfires on every gear when decelerating and sometimes when accelerating. It also will take forever to start and sometimes wont if i dont give it gas. When it does start its a very rough idle. Any thought and or links to a similar post?

[salisch1]

Heres a video. https://www.youtube.com/watch?v=aDQZiG5wedo

[NoFlex]

have you checked timing?

[salisch1]

Originally Posted by NoFlex

have you checked timing?

i checkedthe timing a few days ago and it was set correctly. could it change by itself in such little time?

[jedi03]

Was it auto to manual swap or just new tranny?

[SoundEfx]

Check your plugs to see if you're running too rich or something.

[Crazyced]

Post MAF leak?

[ultimateirving]

Originally Posted by Crazyced

Post MAF leak?

This,
Something is loose like a clamp, coupler or a hole in the vacuum system. Upon decel it's pulling vacuum like crazy.

[SoundEfx]

But I thought a backfire is normally caused by a rich mixture and a post maf vacuum leak would cause a more of a lean mixture?

Educate me oh wise ones.

[salisch1]

Originally Posted by SoundEfx

Check your plugs to see if you're running too rich or something.

one of the plus was very very fouled and it smelled like gas on cylinder 1. I replaced all spark plugs just to be safe and I took it for a test drive. Still backfires but not nearly as much and not nearly as loud.

[salisch1]

Originally Posted by jedi03

Was it auto to manual swap or just new tranny?

whole swap

[SoundEfx]

I am assuming that when you say whole swap, you mean ecu and harness as well.

Change the spark plug wires as well and check to see if the injector(s) are leaking.

[corkscrew]

Sounds like a leaking injector

[ultimateirving]

Originally Posted by ultimateirving

This,
Something is loose like a clamp, coupler or a hole in the vacuum system. Upon decel it's pulling vacuum like crazy.

I was driving today, and i just backfire in every gear on decel i think its just running rich by putting the engine under load... Is your MPG suffering ?

[S-Nation S13]

sounds like a leaky injector,turn car on let it idle for a little bit, shut if off and leave the car over night allow it to sit. remove spark plugs in the morning (do not turn car on) if spark plugs are moist at the tip more than likely you have a leaky injector, if that shit is soaked more than likely your injector o-rings are busted.

[salisch1]

Originally Posted by S-Nation S13

sounds like a leaky injector,turn car on let it idle for a little bit, shut if off and leave the car over night allow it to sit. remove spark plugs in the morning (do not turn car on) if spark plugs are moist at the tip more than likely you have a leaky injector, if that shit is soaked more than likely your injector o-rings are busted.

thank you to every one to had helped. cylineder 1 injectors o ring actually melted and the casing came off and got stuck in the hole. this also caused me to ruin 2 spark plugs. seems like the answer is almost always leaky injector lol

[Crazyced]

Originally Posted by SoundEfx

But I thought a backfire is normally caused by a rich mixture and a post maf vacuum leak would cause a more of a lean mixture?

Educate me oh wise ones.

I'm not entirely sure of the science behind it but I know carb motorcycles can backfire on decel and throttle shuts when running in lean conditions (cold temps, freeflow exhaust, badly adjusted carb, etc). Wouldn't be surprised if that was his issue as well.

EDIT: Basically the fuel mixture on decel is too lean to combust reliably every stroke so the mixture accumulates in the exhaust and eventually combust when the odd firing happens.

[Kingtal0n]

this post touches on a very good point/subject I want to elaborate with

On most engines, like the KA/SR/RB, there is a fuel cut when TPS goes to resting position above a specific RPM threshold. For the stand-alone ECU this is adjustable naturally, but for OEM ecu it is around 1400rpm, it depends on whether the A/C is on or not. Threshold for fuel cut is higher when A/C is on. This helps keep the engine from bogging as it returns to idle.

To paint a picture, you are driving in 4th gear for example, around 40mph, some rpm (say 2400rpm). Your throttle is slightly open for the cruise situation. Suddenly, you lift your foot from the gas pedal.

If you had an open downpipe, or any kind of non-silent exhaust system, there should almost always be one single pop as the final cylinder gets some but not quite enough fuel to burn at such a lean ratio, and this fuel enters the exhaust and makes a slight "POP" noise. The key to this, and the reason I am pointing it out, is that this POP noise only occurs ONE TIME. It signifies that the engine has entered a fuel cut mode, and that none of the injectors is leaking excess fuel. Next time you drive, pay attention when you lift your foot, there is always this one critical POP as the ecu pulls into it's fuel cut mode. Any extra POPPING is caused by fuel entering cylinders that should not be there (leaking injectors). Also note the exhaust system needs to be hot enough to burn the fuel (it might not pop on decell when cold). There is plenty of oxygen in an exhaust system when the car is in decell (the engine is turning but no fuel is going in, it is literally pumping your exhaust full of fresh air. In fact you could potentially free-air calibrate a wideband sensor by allowing the engine to decel during fuel cut, I do not recommend this but the literature on wideband sensors does mention this technique).