Black smoke

[VTECnique]

OK guys, you may be able to help me out.

My mate was behind me when this happened. I was in 2nd & floored it to 3rd, & apparently when i hit 3rd, I got a puff of black smoke. So i asked him if that was the only time it puffed black smoke & he said yes.

I do realise black smoke usually indicates running rich, i know im still on narrowband, but i was going to grab an air/fuel gauge pretty soon to see what im running.

Im also getting a fair bit of backfiring, anything under 4k rpm, when i deccel. Anything above 4k, its fine.

Ive searched around abit about this topic, im going to check my 02 sensor to see if i need a new one or i can just clean it (if possible). Ill also ask me mate if he could smell fuel when it happened, so i may be able to narrow it down.

I had a mech do a service on it a few months ago, in may, he did a comp test & everything was fine.

I have a funny feeling my plugs may need to be replaced. Ive got NGK iridium IX's in it right now, but ive had them in it for quite some time (put them in i think around 100k, its got 185k on it now). Am going to try denso iridiums next time round.

[ECU-MAN]

is your ECU and engine stock

sounds like its running rich

[VTECnique]

yeap, & the ecu aint throwing any codes either...

[VT3C]

sounds pretty normal for a stock ECU on a Bolt-on modified Honda.. if you're really worried, get a dyno test mapping your AFR's.. Rich is fine (it's safe) however you wont be making optimum power and if TOO RICH you can get 'blow-by; where the fuel dissolves the this oil layer that helps seal your piston rings and then you may have oil and fuel pass straight through the rings and this can cause inadequate lubrication of your rings and lead to cyllinder wall damage etc.

[OMG.JAI xD]

If youve got exhaust mods, read up on the thread talking about exhausts.

Has heaps of info on exhaust velocities and all that mumbo jumbo.

To put a long thread to short words.

Basically. If you increase the piping diameter of the exhaust (ie change components, headers, cat, n cat back) you'll be changing the flow of the exhaust gases.
Better flow = a better/higher flow during valve overlap. Describing valve overlap is going to get very technical and too long, but its basically the moment in time where the intake valve and exhaust valves are opened at the same time to cause an effect so the combustion chamber has initial intake flow (the correct term slipped my mind atm). While this happens you have a little amount of fresh air mixed with fuel is dumped into the exhaust system, which in turn gets burnt in the cat.

Now, raising your exhaust flow, causes more of that fresh air and fuel mixture to be dumped into the exhaust n burnt in the cat. In the end. Causing you to have a puff of black smoke when you change gear near redline.


I tried dumming that down and keeping at simple as i can.
If your engine is running fine, i wouldnt worry.
Check your fuel consumption too.

[OMG.JAI xD]

sounds pretty normal for a stock ECU on a Bolt-on modified Honda.. if you're really worried, get a dyno test mapping your AFR's.. Rich is fine (it's safe) however you wont be making optimum power and if TOO RICH you can get 'blow-by; where the fuel dissolves the this oil layer that helps seal your piston rings and then you may have oil and fuel pass straight through the rings and this can cause inadequate lubrication of your rings and lead to cyllinder wall damage etc.

No matter what engine, you will always get blow by.
Oils are engineered to cope with this blow by. Even under the most severe conditions, it will still lubricate the engine.
Unless your ring end gaps are too excessive, you'll get a lack of compression and excessive blow by.
Theres a reason why you need to change the oil every 5-10k kms.
Its suspected the oil quality deteriorates after that many kms.

[VTECnique]

i got a 2.25" catback. About 2 years ago, there was a ver big rattle in my exhaust. Thinking it would go away, i could here it was around the cat area. so a few months later, the rattle actually made its way right to the rear muffler. I have a removable silencer, which is kept on all the time, so whatever it was, was stuck behind the silencer. As i was removing the silencer, out came this big piece of catalyst (honeycomb) from the cat. Ive got the catalyst laying around somewhere, will try to find it & post pics...

Because this bit of catalyst is missing, could this also cause my gear change black smoke? An oil change isnt due til another 5k, i may just have to remove the cat to take a closer look at it... I was going to grab a header for it shortly aswell...

[OMG.JAI xD]

i got a 2.25" catback. About 2 years ago, there was a ver big rattle in my exhaust. Thinking it would go away, i could here it was around the cat area. so a few months later, the rattle actually made its way right to the rear muffler. I have a removable silencer, which is kept on all the time, so whatever it was, was stuck behind the silencer. As i was removing the silencer, out came this big piece of catalyst (honeycomb) from the cat. Ive got the catalyst laying around somewhere, will try to find it & post pics...

Because this bit of catalyst is missing, could this also cause my gear change black smoke? An oil change isnt due til another 5k, i may just have to remove the cat to take a closer look at it... I was going to grab a header for it shortly aswell...

You shouldve said that in the initial post.

Without a cat youre not burning any excess fuel and just letting it straight thru.
Its the same as having a straight pipe/test pipe.
Your car isnt running rich, you just have an emission component faulty. In this case. Your cat.

[VTECnique]

yeah, sorry i didnt mention it before, since its happened a few years ago, i completely forget about it... a New cat should fix the problem?!?! But even with the current cat, it only smokes on high rpm gear change...

[i-jrdm]

pretty sure ive got the same problem with my dc2. ive got a rattle with the cat when i changed from stock to 5zigen catback. i was thinkin the coz the cat back is slighting a bigger pipe is the reason then stock but im not unsure.. and i had the same thing 'black smoke' which i know its running rich and due for a service. thanks for the info anyways omg.jai and bringin the topic up vtecnique. cheers :)

[bennjamin]

any alteration in intake or exhaust on a stock ecu'd car , will result in the car running noticeably richer WOT. Thats the black puff of smoke in the upper rpms. Normal

[aaronng]

yeah, sorry i didnt mention it before, since its happened a few years ago, i completely forget about it... a New cat should fix the problem?!?! But even with the current cat, it only smokes on high rpm gear change...

Normal on high RPM. On a car with a proper working cat, it is a grey puff of smoke that you don't usually notice. So quickly get a replacement cat!

[migoreng]

yeah, sorry i didnt mention it before, since its happened a few years ago, i completely forget about it... a New cat should fix the problem?!?! But even with the current cat, it only smokes on high rpm gear change...

when i engage vtec i leave a trail of grey/black smoke.
it's very noticable in my rear view mirror at night with headlights behind...
:o

any ideas?
my fuel consumption is great, 9L/100km. oil loss is not that bad, ~350ml/1000km

[VTECnique]

Normal on high RPM. On a car with a proper working cat, it is a grey puff of smoke that you don't usually notice. So quickly get a replacement cat!

Well, technically i now have a hi-flowed cat. LMFAO!!

[aaronng]

Well, technically i now have a hi-flowed cat. LMFAO!!

A collapsed cat flows slower than an OEM cat. If you lost chucks into your muffler, then your cat might flow more, but the muffler's restricted. lol

[jrxs-r]

In regards to popping on back off (zero throttle), just check that your TPS bolts haven't loosened off, letting the TPS move about.

[VTECnique]

In regards to popping on back off (zero throttle), just check that your TPS bolts haven't loosened off, letting the TPS move about.

cheers mate ill have a look at it today...

[intk20A]

The black smoke is unburnt fuel, make sure your plugs are good and change engine oil....

Preludes do this on hard acceleration