[chucky101]

Hi All,

So this 440i has been blowing a huge puff of smoke from the exhaust (not constant) for a few months now. It is getting annoying.

I have already changed the pcv diagphram and still has this smoke from exhaust issue.

I just took the car to a bmw mechanic and he did a full diagnostic and found no oil leaks.

He said the smoke dosnt smell like oil, it smells like a bad catalyst.
He also said that he thinks the downpipe is aftermarket (catted) not sure but he said even if the OEM downpipe went bad it'll still make that smoke. (I thought it has no mods, thats what the dealer said)...

Does a bad catalyst actually blow a puff smoke out of the exhaust when you accelerate from stop? And also happens when idling for a few minutes and rev it to 3000 rpm.

I asked him to check turbo seals he said its too expensive to do that, better off changing the whole turbo if i was to do that,

Any thoughts? What should i do next?

Should i change the downpipe to something else? Catted or catless?

What could possibly be causing this smoke?

[im_an_alien]

A BMW mechanic who can't tell between OEM and aftermarket down pipe? Yet he can perform a full diag? Hmmm ....
Might want to get a second opinion before you start replacing parts, DPs aren't cheap.

[chucky101]

Originally Posted by im_an_alien

A BMW mechanic who can't tell between OEM and aftermarket down pipe? Yet he can perform a full diag? Hmmm ....
Might want to get a second opinion before you start replacing parts, DPs aren't cheap.

Yeah they are bmw mechs, they only work on bmw. They do know their stuff, he did a full diag and found a leak in the air intake pipe, he patched it up.

He said he is certain the downpipe is not oem because hes seen them too many times and its shaped different. He needed to double check on the lift but we didnt have time,

However when i previously did a inspection at another mechanic they said its stock and i saw it myself and honestly it looked oem.

Ive seen aftermarket downpipes they are more slim and they have huge logos on them so its obvious.

Anyway regardless if its oem or not, does a bad catalyst blow smoke from the exhaust?
If so it could be the answer to it i guess

(I did have a error code a month ago bad efficieny catalyst, cleared it and it never came back).

It could be linked to his theory

[Wires]

The catalyst needs to get up to temperature before it becomes functional. That's why the car does that higher RPM "startup roar" to pre-heat it as fast as possible.

Once the catalyst gets hot, then it burns the hydrocarbons on the exhaust.

What does the exhaust smell like? Oil is really putrid, if it was a catalyst, then it would smell like unburnt fuel, coolant will have slightly sweet smell.

[chucky101]

Originally Posted by Wires

The catalyst needs to get up to temperature before it becomes functional. That's why the car does that higher RPM "startup roar" to pre-heat it as fast as possible.

Once the catalyst gets hot, then it burns the hydrocarbons on the exhaust.

What does the exhaust smell like? Oil is really putrid, if it was a catalyst, then it would smell like unburnt fuel, coolant will have slightly sweet smell.

I daily this car, around an hour a day so the catalyst is always up to temp when the smoke puffs out the exhaust while driving.

To me it dosnt smell like completely unburnt fuel and it dosnt smell sweet.

It smells more like something burnt like oil or burnt grease (maybe a hint of fuel?) and it sticks to your clothes like you can smell it on yourself all day.

And it also leaves a buildup of black residue on the exhaust tip.

I am leaning towards a bad catalyst, because it does rattle on start up and the mechanic said thats what melted catalysts do as well

[Wires]

Ahh.. yeh, that sounds like the cat in the downpipe failed. Getting a high flow aftermarket will keep the smell to a minimum. Going cat less will smell like an old car.

[rusty_sojah]

So i am curious of the b58's require a OCC at some point like the n54's did. I am new to a b58 and just did a catless DP but had a bad dream that i started blowing oil and smoke again like my old n54 did and i couldn't find a shop to install an OCC for on the tiny ass island i now call home. All very realistic and scary, yeah