Help...backfiring

[DavetoExtreme]

Hey guys, I get an occasional backfiring while accelerating or decelerating at times What could be the causes? Could it be faulty spark plugs or a clogged fuel filter, clogged fuel lines or injector??

[~Vēġó~]

how's your fuel economy????

[DavetoExtreme]

no noticeable difference but there may be some small difference

[TeamH2O]

fuel filter check that first, then check fuel pump(float may be clogging up, depends on how long you had the car), then plugs i guess

[DavetoExtreme]

will do

[DIESELTRINI]

I fail to see how lack of fuel could cause that... WHere is your backfire? Through the intake or exhaust?

Is the engine carbureted or fuel-injected? Have you checked your ignition timing to ensure it is correct to specs?

[DavetoExtreme]

Yeah boy Inshan the fuel part puzzling me too ....The engine is fuel injected...backfire is in the exhaust.....Ignition timing is a factor since its an occasional backfire or it could either be the plugs also...my suggestions but I'll also check the fuel filter etc....I'll let you all know the outcome but occasional backfiring is weird to me

[God Bless the Black Top*]

running straight pipe? may be a leak in ur exhaust?

[honda4life]

friend of mine had his car backfiring real plenty and it was because of the fuel pump

[Precious Roy]

You could probably try running a top engine conditioner through it too to get rid of any combustion chamber deposits

[Strugglerzinc]

Backfire is almost always caused by wrong ignition timing or unburned fuel being ignited in ur exhaust. Ignition problems should give you a difference in how d car drives.Check ur plugs.One could be goin bad.Could change to hotter plugs.

[DavetoExtreme]

Slapped in some denso iridium plugs IK16's .....and a new fuel filter (that wasn't really the prob), Pump was ok....problem solved...those denso's do make a difference Thanks peoples ...

[Strugglerzinc]

friend of mine had his car backfiring real plenty and it was because of the fuel pump

I honestly dont see how a fuel pump could cause backfiring. could anyone explane cuz i wanna kno Y.

[DavetoExtreme]

An air/fuel ratio is said to chemically correct or stoichiometric at a 14.7:1 air/fuel ratio. The oxygen sensor (O2S) monitors the oxygen content of the exhaust gasses (in comparison to the outside air) and sends a message to the car’s computer to either add or subtract fuel from the air/fuel mixture. By constantly sensing the oxygen levels the O2S can determine how well the combustion process is working.

A correct air/fuel mixture will be evident by the correct levels of unburned oxygen in the exhaust gas. The O2S is constructed of material that chemically measures the difference in the oxygen content in the ambient air compared to the oxygen in the exhaust gasses.



The O2S sensor’s has a metallic cover protecting ceramic body made of zirconium dioxide with gas permeable platinum electrodes on the surface. The chemical process occurring between the surface exposed to the exhaust gas and the surface exposed to ambient air creates an electrical current. When the residual oxygen level of a chemically correct or stoichiometric 14.7:1 air/fuel ratio is detected the electrical current is 0.45. If the mixture is rich the reading will be greater than 0.45 volts. A lean mixture will be less than 0.45 volts. The chemically generated output range of the oxygen sensor is usually between 0 and 1.1 volts with a normal operating range between 0.2 to 0.7 volts.

The voltage results from the O2S are sent to the ECU, which then regulates the amount of fuel pumped into the engine (air/fuel mix). The objective is to reach a stoichiometric mix that generates a 0.45-volt reading by the O2S. When operating correctly there is a continuous crossing of the 0.45-volt mark (the "O2 cross" mark). The effectiveness of an oxygen sensor is measured in the number of "O2 cross" counts. The more O2 cross occurrences means the better the sensor and computer control systems are working. This constant feed back, monitoring result and adjustment is known as a closed loop system because the air/fuel ratio is regulated only by the results of the O2S.

In a nutshell...you need a rich mixture for a backfire to occur in your exhaust If your fuel pump float is clogging then theoretically you won't have backfiring on acceleration but on deceleration, the ECU may not be able to effectively control fuel flow (irregular flow due to a pump probs) so you can have an occasional backfire due to some unburnt gases moving into your exhaust pipe which could ignite on your next cycle especially if you accelerate afterwards:wink:

....just my 0.01cents...feel free to add to it

[Alpha_2nr]

Check your ignition timing. Your timing's gotta be off. Especially if your fuel consumption is normal.

Maybe you can either retard or advance your timing to suit your driving style, and maybe that could clear up the whole backfiring issue.

[Alpha_2nr]

I seriously doubt that putting in Denso Iridium spark plugs can solve a backfiring issue....unless maybe the spark plugs you were using before were incorrect (temp rating) to begin with.

Backfiring -----> Ignition Timing ------> Check that out first.

[DavetoExtreme]

If timing is not optimum, regardless of what plugs are used, you would still have backfiring....so if the prob was resolved then I guess it was the plugs..will see in the long-run

[zer0xp]

An air/fuel ratio is said to chemically correct or stoichiometric at a 14.7:1 air/fuel ratio. The oxygen sensor (O2S) monitors the oxygen content of the exhaust gasses (in comparison to the outside air) and sends a message to the car’s computer to either add or subtract fuel from the air/fuel mixture. By constantly sensing the oxygen levels the O2S can determine how well the combustion process is working.

A correct air/fuel mixture will be evident by the correct levels of unburned oxygen in the exhaust gas. The O2S is constructed of material that chemically measures the difference in the oxygen content in the ambient air compared to the oxygen in the exhaust gasses.



The O2S sensor’s has a metallic cover protecting ceramic body made of zirconium dioxide with gas permeable platinum electrodes on the surface. The chemical process occurring between the surface exposed to the exhaust gas and the surface exposed to ambient air creates an electrical current. When the residual oxygen level of a chemically correct or stoichiometric 14.7:1 air/fuel ratio is detected the electrical current is 0.45. If the mixture is rich the reading will be greater than 0.45 volts. A lean mixture will be less than 0.45 volts. The chemically generated output range of the oxygen sensor is usually between 0 and 1.1 volts with a normal operating range between 0.2 to 0.7 volts.

The voltage results from the O2S are sent to the ECU, which then regulates the amount of fuel pumped into the engine (air/fuel mix). The objective is to reach a stoichiometric mix that generates a 0.45-volt reading by the O2S. When operating correctly there is a continuous crossing of the 0.45-volt mark (the "O2 cross" mark). The effectiveness of an oxygen sensor is measured in the number of "O2 cross" counts. The more O2 cross occurrences means the better the sensor and computer control systems are working. This constant feed back, monitoring result and adjustment is known as a closed loop system because the air/fuel ratio is regulated only by the results of the O2S.

Please give credit to the people who wrote this article..
http://www.miata.net/garage/KnowYourCar/S3_O2.html

[DIESELTRINI]

Davetoextreme, you copied a nice explanation of how the O2 sensor works, but it is totally irrelevant to backfiring. How would a clogged pump sock (you said float, which is the gauge, but I assume you meant sock) result in a rich condition? Wouldn't it result in a lean condition if the pump is being starved on the supply side?

The ECU would see the lean conditon from O2S feedback and would try to correct this condition by increasing long-term fuel trim, but it would not make much of a difference if the total supply is compromised.

That is my 0.02 on this one.

[DavetoExtreme]

That's why I said on deceleration...not acceleration and the explanation was just to show how the ECU manipulates the fuel flow.......but nice point made there

[DIESELTRINI]

Unless you are talking about a very old fuel-injection system, or maybe a carbureted engine, there would be no fuel delivery upon deceleration (throttle release). So, decelerate would always be a lean condition.