Why Do Cars Backfire?

Why do cars backfire? A backfire occurs when combustion takes place outside of the cylinder. Backfiring can be used to describe combustion occurring through the intake (traveling backwards) or through the exhaust, although this is also called afterfire. In this video we'll take a look at how an engine could have combustion travel up the intake.
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Afterfire (Backfire): • Why Cars Backfire - Af...
Ignition Systems: • Ignition Systems - Exp...
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Fuel Injection: • How Fuel Injection Wor...
My next video will be "afterfire." Be sure to check this out to see how combustion could occur within the exhaust.
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[@EngineeringExplained]

Yes, I've covered this in another video Check out the first link in the description "afterfire" to learn more about this topic!

[@BlizzardHockey4432]

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[@gdltiii]

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[@EngineeringExplained]

Great to hear, thanks for watching!

[@EngineeringExplained]

Yes, it's quite problematic if it starts coming back through the intake. Also, check out my video "why cars backfire - afterfire" which explains when flames exit the other way.

[@EngineeringExplained]

Thanks! Glad you enjoy the videos!

[@EngineeringExplained]

You're welcome, glad you enjoy the videos!

[@Sully9711]

I'm a first year engineering student and this KZbin channel just astonishes me with every video. I'm making all sorts of connections to knowledge I already have and it's explaining things I've always wondered. It may have helped me find my passion in engineering

[@EngineeringExplained]

Glad to hear it, thanks for watching!

[@EngineeringExplained]

Haha though I understand completely. I always wanted a channel like this to watch. Couldn't find seem to find one, so I made it. That way other people can be lazy and find out in 10 minutes rather than 3 hours how something works. From an efficiency standpoint, I think it's terrific; and efficiency is all us engineers care about haha :)

[@EngineeringExplained]

Great to hear, thank you!

[@EngineeringExplained]

Because the pressure may not begin to increase enough until it reaches TDC. Think about it like this. The piston is moving up VERY fast. You make the spark shortly before it reaches TDC. By the time the air fuel mixture is fully ignited and expanding, the piston has already hit TDC. It's all about timing it right so that you get the maximum amount of expansion.

[@shamaYahu8635]

Hi, I have a 03 Jeep Grand Cherokee with a 4.0L that I installed a distributor to; kind of like the one you have on your drawing board. I also installed a carburetor. I don't believe that my valve timing is off because the 03 Jeeps have a timing chain and I never messed with it. I'm having backfires, and I believe it's the timing like you said in your video because the car gets ready to start but then it spits out flames or gush of are out the car carburetor, then the whole engine stops and I have to turn the engine over again.

[@EngineeringExplained]

Misfire typically refers to a cylinder not firing. For example when a cylinder doesn't fire it will throw a "misfire" code to your OBDII. The engine will be shaking.

[@jamesminner5861]

You answered my belief that I'm trying to verify for my old dodge well. Thanks! Now on to confirm through fixing the wires. Great diagram and explanation.

[@xaviergarza9414]

Not to much has changed in today's videos! Love it man

[@Centigonos]

You, Sir, are one of a few KZbinrs who make this site worth visiting!

[@SharkSugarr]

Great videos, man. I really learn a lot! You're great at explaining things.

[@EngineeringExplained]

You are correct in your description of detonation. It's not the same.

[@MrAjallday91]

Just wanna let you know that you've helped me out a lot...ive got an srt4 and there ain't a lot of room under the hood..im what you'd say "new" to cars. So you're videos really help me understands whats going on in the areas I can't see. I'm now addicted to your videos lmao HAVE A GREAT DAY!

[@EngineeringExplained]

Sounds like a dream to me. Though this is done with nitrous where the mixture of N2O and fuel is sprayed together.

[@jlopez65]

Awesome explanation! I had a backfire problem along with rough idle, almost no acceleration power, and the engine would die on a 1987 Nissan Maxima. Problems all solved; 1.. Ignition Timing 2. Air Mass Sensor 3. #5 injector was stuck open 4. Bad Spark Plug wires.

[@bullridermusic2054]

Mate your channel is great, keep up the great videos!

[@lukee49]

Sooo... fuel injected cars can't really back fire?

[@EngineeringExplained]

Bayside Bluee Well, most people refer to back fire as flames coming out the exhaust, which can certainly happen with EFI. That said, the problem I'm speaking of in this video might still be able to occur with port injection.

[@JohnSmith-xt7fz]

Engineering Explained People also map in Pops and Bangs, but that's intentional over fuelling. Also have ALS and LC, that also causes 'backfires'.

[@maxavatar3]

+Bayside Bluee My saxo, has it's engine head worked on a.k.a the valves size so more gas can come in. but just a bit, before the engine heats damn it's noisy xD

[@rmsvideos1335]

+Nissan Supra AMG If its not direct, based off of what he said, it could still happen from a bent valve or misplaces spark plugs because there would still be some fuel. But even then I don't think it would be as bad because it would only be the fuel that was meant for that cylinder, whereas when its supplied through the carb there is a ton of fuel in there at any given time.

[@victoraberdeen1299]

I discovered just yesterday that fuel injected vehicles can and do backfire.The cause being faulty fuel injectors or faulty/incorrect coils.

[@EngineeringExplained]

Very welcome, thanks for watching!

[@numinous4789]

A better question: why do so many "car guys" wrongfully call afterfires backfires? Yep, they're two totally different things. As this video points out, backfires have to do with the "front" half of the engine, between the throttle plate and the intake valves, basically. Afterfires, alternatively, deal with the back side - from the cylinders and through the exhaust. Backfires are potentially far more harmful. Afterfires aren't nearly as harmful, but can damage catalytic converters. Most of the folks who have a lot of afterfiring going on are catless anyways, though.

[@Hanger995]

You're A better teacher than A LOT of mechanics I know. I'm 17 and learning so much necessary information! Now I can talk 'car' with the fello motor heads on our race team.. Thanks man.

[@CJforUSA]

Thanks for taking time out of your day to share your knowledge with us.

[@EngineeringExplained]

I'll go over those two in the next video. Cheers!

[@loodi69]

Thanks alot for the videos man theyre so informative and simple to understand. Keep up the great work :)

[@lycanchimera]

Hello EE. Thank you for putting this up!

[@EngineeringExplained]

Delayed spark and some have extra fuel dumped into the exhaust manifold - hence the combustion goes all the way out the exhaust.

[@GermanGameAdviser]

this channel is GOLD

[@EngineeringExplained]

Probably has a richer fuel mixture than on the stock tune. As far as if that's okay, not really sure. It's certainly not beneficial, but I don't think it would cause too much harm.

[@runalongnowhoney]

Second theory is that exhaust / flame front is somehow lingering in the exhaust port from the previous powerstroke, and when the intake valve opens during overlap with the exhaust, the fresh charge is ignited and expands into the open intake port (with fresh air and atomized fuel eager to burn). I would really like to understand what is actually going on with this issue.

[@shinzantetsu]

OMG, i just found out about this channel. This is awesome... Love nerdy shit like this!

[@dewalt607]

Are you going to make the Redline video? By the way, honestly your such a boss, I really appreciate you making these videos, its soo simple and helpful. Thanks and keep up the fantastic work!

[@VinuraVinura]

Can you please do a video on lift and duration and their effect on engine torque? Cheers, your videos are great!

[@EngineeringExplained]

Camshaft - High Lift and Duration - Increase Horsepower

[@EngineeringExplained]

Thank you!

[@captainchaos0666]

Question for you good sir. I always assumed that popping and burbling in the exhaust was caused by the exhaust valve opening and closing. Am I correct in assuming that it's sound waves and the timing in which they exit the exhaust system? I always thought when aftermarket mufflers are installed, you would hear it better.

[@matthewisaacs7253]

Love the depth of your question ...... sounds like the type of question I'd ask. Always wondered why intakes make the sounds they make

[@paulscontainersltd.4020]

Love your explanations Keep it up I’m just subscribed to your channel

[@EngineeringExplained]

Great, thanks!

[@LowBackPain94]

Hey I was thinking about buying an electric dump valve for my exhaust for my turbo car. Would having the electric dump valve have too little back pressure for significant gains? In videos you can see some exhaust gas still managing to go through the full exhaust, resonator, cat, muffler, and out. Basically the exhaust gas isn't all flowing through the electric dump valve but splitting. Not sure if I should buy an electric dump valve to install after the down pipe or not. I don't want to lose power. I already a upgraded 3" turbo back but I do have a hi flow cat and a resonater because who wants to get pulled over all the time?

[@micheals1992]

I heard an explosion sound in my car yesterday, it came from the area of my right rear tyre and sounded just like a blowout. at first it thought it was a blowout. But the car seemed to be handling fine, I pulled up and checked my tyres they are all fine, I checked in my boot and there was nothing in there that could have caused it. The only thing I can think is that it was either the spare tyre, the lorry that had just passed me on the opposite side of the road or a backfire (the exhaust is located next to right rear tyre) it was wet so I couldn't check but I'm also concerned my brake pipe may have burst.

[@samhicks97]

My 64 Dodge started backfiring/sputtering/no power. after a spark plug wire maintenance, found out that either my distributor cap is cracked or plug wires are incompatible. *Your video helped me where to look for problems with backfiring. Thanks!*

[@wonniewarrior]

I have driven Dual Fuel (LPG / Unleaded) cars for decades. The older style gas injection through the carburetor would often blow out the air filter box if it backfired, which it did a lot with old style gas converters with a rubber diaphragm. Would install spring expansion clips for the air filter box so when it backfired, it would allow the air box to let the pressure out without destroying the clips, and even damaging stuff under the bonnet. I have not had the problem since I switched to cars with direct gas injection, or MPI with throttle bodies and fuel injection setup.

[@jackthompson1382]

Can you please make a video explaining reverse pattern cams vs. single pattern vs. dual pattern cams? With special emphasis on the reverse pattern cams (ie: the intake duration is higher than the exhaust) that are becoming increasingly popular due to better head designs like on LSx, GM push rod motors... etc. Thanks! You rock!

[@MustangGuru]

Go one for yah, I have a 2015 Roush stage 3 supercharged 670hp. Sometimes , maybe once a week or month, within the first 20mins after starting it. And crusin at about 40-50mph in 4th or 5th gear I can give a rapid hit of the throttle to just under half throttle it will burble back thru the intake system. After that it fine, so what do you think is going on?

[@EngineeringExplained]

Thanks!

[@oXelienanXo]

I'm a fully qualified mechanic and I still find your topics and explanations very interesting!

[@DARKELLAKEL]

So on my Conquest TSI the boot from my MAS to my turbo was sucking in air, causing it to backfire VERY hard during boost. Could it have done any damage, and if so to what?

[@clarakoussaifi203]

Very informative! Thank you :)

[@SRodriguezProduction]

Your videos are excellent. Thank you!

[@EpicFishFingers]

So how bad would a carb backfire be? Does the bonnet do a somersault or is there just a loud bang?

[@pokealong]

+EpicFishFingers Fairly certain it's just a loud banging sound.

[@battikhy199]

Just a loud bang in case the air filter is removed, or a really muffled bang in case the filter is on (I have a carbed engine so I've come across it all)

[@djurovicgiorgio]

Hey teach, what about when cars crackle and pop on the overrun, like the mini JCW or say an m2 or mostly any performance car today (porsches etc)? Build up some revs, take your foot off the gas and enjoy the symphony! What's the reason behind that? Also how would you mod your car to create the popping on the overrun? Need to figure this out, want my 220 to pop so bad lol

[@EngineeringExplained]

Absolutely, check out the "Automotive Careers" link on the "About" tab of my channel page.

[@SunnahTaqwa]

Hi there! Thanks v.much for ur helpful videos... i was wondering, could u pls do one on the difference between BMEP and IMEP and their importance?

[@justindelvalle4361]

@ tr3ning that is an after light or after fire from too rich of a mixture. Unplugging the rear O2 makes the ECU default to a richer Air to fuel ratio to save the engine. The rear 02 in most situation is there to monitor catalyst efficiency and be the final reference for the ecu to target stoichiometric ratio in closed loop and in open loop fueling it is ignored. Without the resistance value from the sensor it the ecu thinks its too lean and calulates a longer duty cycle to try and "correct" the issue. It adds so much fuel that it cant burn it all and it gets dumped into a hot exhaust pipe and it after lights or after fires

[@Back_To_Pray]

Do weather conditions affect the amount of backfire? I notice my car will pop more on colder days, but not every cold day. Does humidity or other conditions have any affect?

[@sp00nix]

I had my intake back fire in my face when i was adjusting the idle mixture. The directions had the direction reversed for turning the potentiometer so i accidentally made it super rich. This was on the crude Bosch LH 2.2 system (early 80s), it used a blinking LED to indicate mixture readings form the O2 sensor.

[@MajedTaib]

hey Jason, I want to install exhaust flamethrower on my car and I knew that I should rip catalytic converter to get the flames, my question is, should I rip the resonator too? (if so, it's going to be straight pipe till the muffler) or I will get flames with resonator on? really need your help and I appreciate that. thank you.

[@runalongnowhoney]

I am trying to understand why my single-cylinder (492cc) air-cooled motorcycle engine sometimes backfires through the carb. It usually happens on re-starts, with the engine at normal operating temperature. Compression checks in tolerance. Valves look fine (visual inspection through each port). New Spark Plug. Main and Slow jets have been increased in size to match free-flowing intake and exhaust modifications.

[@Oblithian]

Can you make a drawing illustrating exhaust crackle when letting off the throttle? (Not that it's a bad thing, it just sounds cool)

[@gamer6654]

Oblithian yeah that happens to mine as well, that's not considered a backfire, right?

[@YachtLife]

I believe that comes from fuel being dumped and firing off during deceleration

[@mihan2d]

@@YachtLife Why would you dump fuel on the modern EFI engine I wonder...

[@YachtLife]

@@mihan2d idk, go back a year and ask again

[@Seyoum14]

Yes please, I'm looking forward to that video.

[@EngineeringExplained]

There's no bad place for learning!

[@AlwaysOnP0int]

What if this only occurs at a certain throttle position, 1/4 throttle for example, idle, half, 3/4 and WOT are clear. Could it be caused by something else, i.e. dirty needle jet?

[@salamander5703]

I have a Formula Ford 1600 race car which emits loud pops and bangs on overrun. It runs fine and has no bent valves etc. It seems to be cured when I seal up the exhaust. There are several sleeve joints which get loose as it heats up and cools, so could let exhaust out or air in. It has a silencer at the end of the pipe. I'm just curious why sealing the exhaust should cure it. Any ideas?

[@strungout25]

Great videos! I learn something new every time I take a dump.

[@praneethvarma5158]

You always make complicated things easy to explain. Thanks keep it up😀😀

[@gospodinkenobi9903]

Ah yes, KZbin algorithm keeps me up to date with new uploads!

[@EngineeringExplained]

It's only 1 week away! I do appreciate that everyone is endlessly curious. I am too, but I'm just one man and have to pace my videos!

[@Psycho9263]

Sometime raw gas fumes make their way out of the exuast valve when the timing is off or if you have a faulty ignition coil. The exaust pipe is all full if unburned fuel and when the spark returns, all the gas explodes in the exaust pipe. POW! We used to do that by turning the key off and on when we were kids.

[@sante1965]

Your videos are the best!

[@ljubomirmilojevic2509]

Can you explain variable-geometry turbochargers anytime soon ? Great vids btw !

[@cardoode]

Exhaust system back pressure, can you elaborate if its needed or its always present at various RPM ranges and whether of not the engine can do completely without it by using a free flow exhaust. Please help me out. Topic does not have much clear understanding elewhere

[@Cardfold11]

well thats quite impressive. it makes all of us seem lazy, you are doing all of the work for us haha!

[@heyyyyyynow]

Your channel is awesome.

[@pancho.shepherd]

Thanks for this vid i always asked this too myself! :D

[@EyebrowsMahoney]

Backfires are more common on carbureted cars where vapors can sit in the intake plenum, however this can still happen in EFI equipped vehicles where timings are off or plugs are wired wrong and other situations (as explained in the video). They won't cause immediate failure, however they are liable to cause serious engine damage if you do not stop the engine and attempt to rectify the problem. Occasional backfires are common when diagnosing ignition problems and are not of an immediate threat.

[@OneManArmy4Life]

Great vid as usual.

[@Jabid21]

Correct me if I'm wrong: a multi-port fuel injection system is less likely to backfire as air-fuel mixture is present near the intake port of one cylinder that's currently in its intake stroke.

[@CarlosLopez-uw9sz]

my understanding of this video is if the vehicle is back firing, it wont pass Emissions or the engine has a problem is this correct?work at a mufflers Shop and customers tell me they want loud exhaust and they want it to backfire.... so i am doing research on backfiring really mean.

[@mewnbewst2v173]

can you explain a "back firing system" as referenced in a tv show "Initial D" in a video?

[@deathseal08]

my b20b in my da integra is backfiring only on cruising speeds but not when i floor it or drive very slow what might cause this?

[@JaspersGarage]

I have a single cylinder 4 stroke go kart, and sometimes when starting it with the air filter off it backfires and flames come out of the intake. Does this mean my intake valve isn't shutting properly or is there another possible cause? many thanks, great video btw

[@diego87tennis]

Cool vids man. Very informational. Do you have a video explaining the muffler? Is it bad to install a muffler delete?

[@EngineeringExplained]

Mufflers - Explained

[@FatGreenSheep]

I’m getting a backfire out of my 318 magnum engine(Dodge Ram) when it’s cold. As soon as my coolant temp gauge starts to move(130 degrees), it goes away. I know I have my wires correct. If I don’t get any backfire once it’s warm, what could be the cause?

[@pimpmyforklift]

How would you explain a Mercedes Benz cla 45 amg to crackle and fart in Sport mode and in Eco mode their is no crackle or fart . How does making more flow exiting the exhaust system create such awesome noise . BTW CLA 45 is a wicked car :)

[@EngineeringExplained]

Perhaps a bit richer air/fuel mixture.

[@ibradeybunch]

The backfires you here in Mercedes is actually fake. But I don't know how they do it.

[@matthewisaacs7253]

Had you considered the scenario where the carb is running lean and the air/fuel mixture ignites before the valve sending fire back to the carb ..... quite common with a pair of Dellortos in a VW Bug

[@oogabooga1211]

cant it also backfire if the springs resetting the valves cant keep up with the rpms?

[@japoniumbr]

just a curiosity: my friends had this cb400 revo (fuel injected) that when they downshifted they kinda popped a bit.. what was that? :o

[@EngineeringExplained]

There are more collars and more gears. Check out my video "sequential gearbox." Similar idea.

[@Alexgomez411]

I'm having this issue at idle it will lightly pop..and under hard acceleration it pops out the exhaust and carburetor.....hope it's just timing not water in the tank

[@monovale442]

so I have this problem with my truck I own a 98 ford f150 4.2 v6 model and the engine backfires while speeding up and when starting sometimes and it stalls while driving. I already replaced the ignition coil, new sparkplug with cables, crankshaft position sensor, and the air intake sensor. my truck still does the same I really don't know what it is, it can be one small thing but you know I'm not a mechanic so I don't know. so plz let me know if anyone knows anything about this problem I would really appreciated thank you

[@alessandromachi1010]

Can timing be adjusted by the sound the engine is making as the distributor is being turned?

[@custommotor]

Actually Ziad Farghaly if the ignition is advanced too much (eg. a couple teeth off on a distributor) it can fire the spark early enough to catch the valve still open. It has to be extremely early, but I've had it happen on a 3rd gen camaro tbi injection. Lite the whole mixture up in the intake and backfired out of the intake. Newer cars would have to have the timing belt/chain put on wrong for it to happen which will blow the plastic intakes off.

[@Phillies4life2008]

Can you explain or do a video on a single carb vs. dual carbs?

[@midlan6]

I heard about backfire (and explosion of intake as result) when bump starting the vehicle moving forward with accidentally in reverse gear.

[@AllenGeiger]

Forgot to mention throttle body injection. Not very common, but has an air/fuel profile in the intake very similar to a carb engine and would also be susceptible to backfire

[@Martin1519]

I started getting a little backfire after installing a full exhaust set up on my ATV. What do I need to do to get it running right?

[@EngineeringExplained]

Thanks for watching!