Popping Sound from Exhaust

ShutterBug SG

Hey bros and sis.,

I have a souped up van, and a souped up car.

Question is; lately my heavily modded van has been producing popping sound from its exhaust when i let go of the accelerator above 80Kmh. It begins with a series of burbbling sounds then a poppy-pop-pop. But the acceleration is really almost a spiritual experience! However, my car also produces burbbling exhaust sound when engine braking. But no popping noise.

I left the van to a friend of mine to further mod it while I was away. Wonder what could he have done with it??

Any ideas, bros and sis?

Kr0n SG

Wow misfiring? Sounds like he rally-specced your van while you were away hehe. Mr. Green

Carribean_blue SG

Hi bro,

Looks like you are experiencing backfiring.

Having said your van is modded giving better performance, i assume that you are now running on a richer air/fuel mixture than stock. I also suspect that your exhaust might have a little leak.

The exhaust leak is probably the cause of the bubbly sound you were mentioning.

There are a few reason of backfiring.

I suspect for your case:

its when you release the acclerator i.e. to change gear or just backing off the throttle when cruising (especially at high rpm since yours is a van travelling at 80km/h), unbunt fuel due to the rich mixture (due to you accelerating) will still be momentarily present and not be fully ignited in the combustion chamber. It flows to the hot exhaust and if there is enough of oxygen i.e. maybe due to exhaust leak, there could be ignition of the air/fuel mixture in the exhaust, causing backfiring.

Check out with the guy driving behind you, a momentary burst of fire due to the backfiring might occur from the exhaust!!! Wink

One way to fix this is to seal the leak in the exhaust (if there is one), run on a leaner air/fuel mixture (be careful, too lean and it will lead to a MISFIRE! which is BAD FOR THE ENGINE). Shocked

ShutterBug SG

Now that it's my friend's turn out of town, I can't find out what he did to my van. But all I can say is, it doesn't drive like my normal already souped up version, it drives more like a friggin car!

Horrendous pick up even on 5 gear!

Not to mention a slight increase in fuel consumption...

Kinda like it though... hafta watch out for TP - dun want a TP to notice how my van sounds...

Thanks for you people's advise and feedback, although the entire exhaust system was already moddified, I'll still check for exhaust leak just in case.

By the way, is all this extra torque bad for my van's drive shaft since it's rear driven?

Kr0n SG

Carribean_Blue: Isn't the running too lean part supposed to be premature detonation? Which causes knocking? I'm guessing that there's a high chance his van's got a turbo in it? Or does it not have?

ShutterBug: I think you might want to check that one up.. Too much torque and your driveshaft might give way. But then again, if it was designed to carry heavy loads, it should be able to withstand quite a bit of pounding. I doubt your manual will have the max. torque allowable ratings though... Hope that helps.

tailslide SG

2 possiblities.

either ur fren installed an anti lag system onto ur van or retuned the a/f to make it run richer.

option one seems unlikely since it'll activate each time u release ur accelerator (not juz at 80 km/h). seems like option 2 is the likely scenario. contrary 2 popular belief, its not the case that unspent fuel igniting upon contact with hot exhaust that causes the presumed secondary combustion. the fact is ur exhaust pipe/ extractors will never get any hotter then ur combustion chambers/engine block itself.

the release of ur accelerator causes a momentary starvation of air molecules entering ur combustion chambers. owing to the nature of a richer fuel map, the secondary combustion is the result when blowby of unburnt fuel (not enuff air molecules to burn with the additional fuel) as ur exhaust ports open and the unspent gases in one chamber pushed out during the exhaust stroke suddenly gets a breath of fresh air (literally) when it meets with minute amounts of oxygen from other chambers during deceleration, causing an uncontrolled combustion and the "pop" sound u described, accompanied with an occasional display of flames spewing from ur exhaust tips.

dun think u have a leak in ur exhaust. if u did, i'd be sounding like a harley during idle. Wink

tailslide SG

detonation occurs more likely as a result of poor ignition timing coupled coupled with other factors rather then juz the result of a lean a/f mix. u can basically run an engine lean as hell with the right ignition timing at the expense of overheating the engine if u wanted to. these other factors include a lean a/f mix, higher compression, poor fuels, higher cylinder pressure/ temperatures etc. none of these alone contributes to predetonation without the presence of poor ignition timing.

Carribean_blue SG

Thanks tailslide for the explanation! I am always learning something new! Wink

Hi Kron,

from what i understand, misfiring is usually caused by spark plug failure; the air/fuel ratio is out of balance to ignite; or loss of compression.

With the air/fuel ratio too lean, there will be lean misfire. This can be due to insufficient fuel pump pressure, fuel pressure regulator, fuel injectors.... etc.

Thus an example in a car with turbo, if too high a boost pressure is set, and the fuel pump and fuel injectors cannot handle the fuel required for the air/fuel mapping, it will misfire due to the lean mixture.

Wink

bo liao SG

Hmm..Hi,, may i know what make /model is ur van??
Cos i also hv a car & van...so..
BUT...1 thing i dun understand how u make backfire from diesel??the combustion is not as high as petrol & van dun hv sparkplug(only hv glowplug)...how to make the popping sound?? Rolling Eyes Diesel vehicle's power is either limited by the richness of diesel going in & the pressure from the fuel pump...when bloody rich only make black smoke/super many soot..... Question

Do u hv re-mapped/changed euc or using any piggy-bag??

Ur 5th gear also damm powerfull??....Do u mean start from stop also powerfull or when travelling then change to 5th gear also powerfull?? So if from 5th gear u pull got feeling, should be got turbo the got tis effect...

Rear driven means rear wheel drive?? LiteAce??

ShutterBug SG

bo_liao,

It's a petrol van. I don't like diesal because of the smell of diesal, and black smoke problems. Also, don't like the sound of diesal engine in idle. Sounds like a taxi.

ShutterBug SG

Anyway, I just checked out my van with a another friend following behind, but cannot see any flames or sparks or whatever. But went into his garage and blow throttle in darkness, can see blue flame when it pops.

So I want to remove whatever my friend put in because I think can kenna pulled over by TP at night.

ShutterBug SG

bo liao SG

Orh....i still tot how come diesel can make backfire, then u gotta teach me..i also want to do it..hehe..pai say pai say...hahahaha

If its petrol, then the theory is the same as cars liao..hehehe...

By any chance, last sat u got go (originally is the queenstown club-behind remand), then go taman jurong, then later in the night is the Fort Rd carpark....then last stop is the Tuas West Rd..?....... Wink

ShutterBug SG

bo liao,

No lah, I don't go around much. I do go to Tuas everyday, but seldom make use of all the mod van's power. I'd say I hardly speed above 80Kmh, mostly between 70-75Kmh. Overtaking is a different number - 90-110Kmh. Breath taking!

have to apply brake extensively to bring down to 70-75Kmh getting back into lane.

heheh.. fun lah.. but don't intend to break law. But I like it when some other van try me on expressway. They'd be left wondering what I'm driving actually. hehehehe
But I must also admit there are others like me as well, super modded van owners are out there.

I know one guy who's a vendor supplying goods to general stores in HDB estates. Walao, he cut his front suspension until you can see the side profile like a giant door jam. Inside van, is like inside disco joint. Giant subwoofers on both sides, complete with flashing neon lights and everything. I always ask him, how you here people's horn? He said; "Use you eyes lah! Use your eyes, use your eyes!" I say; " oorrrrrr.... ok"