sr20det oil smoke on decel

[joshfng]

Hey everyone. Pretty new to 240's and sr20's and am having an issue. My sr20det blacktop is having an issue. It smokes randomly after a large decel. If I take the rpms up and engine brake down, when I get back on the gas a puff of blue smoke will come out the exhaust for a few seconds.

My first thought was turbo oil seals so I pulled my charge piping and there are no signs of oil in them. I pulled the filter pipe off and checked for shaft play and oil and all is good, zero shaft play. It's a fairly new isis rs turbo swap from what I understand.

I checked my pcv valve also and it appears to be functioning properly. Only opens one way and not the other. I did notice there seems to be oil in the black lines running off the tee on the valve cover into the intake pipe and into the black catch can near the exhaust manifold. Is that a sign of something wrong?

The engine pulls strong, no sputtering or missing. I'm going to do a compression test to be safe but I'm hoping there are some other things to check first. Any help would be great!

[Mikester]

Soak your PCV valve in gas till it rattles freely...

As far as the oil in the line back to the stock catch; that's completely normal. The puffs of smoke could be a little bit of blow-by. Do a compression check... Also take a look at your spark plugs & see if there is evidence of oil burning in the combustion chambers.

[Croustibat]

If it is random, it most likely is a turbo seal problem, exhaust side. Usually happens after installing a less restrictive exhaust / elbow/ downpipe.

If it also happens when changing gears, this means "pain in the ass" leaking valve guide seals.

[joshfng]

Soak your PCV valve in gas till it rattles freely...

As far as the oil in the line back to the stock catch; that's completely normal. The puffs of smoke could be a little bit of blow-by. Do a compression check... Also take a look at your spark plugs & see if there is evidence of oil burning in the combustion chambers.

Spark plugs look good. All four are the same color and it appears to normal burn types. White like color, no signs of rich fuel or oil burning on them.

[Danial]

how about shaft play on turbo? Any signs of leaking on turbo?

Do you have an oil pressure gauge?

[joshfng]

how about shaft play on turbo? Any signs of leaking on turbo?

Do you have an oil pressure gauge?

I don't have an oil pressure gauge. I pulled the piping off the turbo and there are no signs of oil and the shaft does move side to side or up and down. It is an ISIS unit though and I've hear good and bad things about them. I didn't check the exhaust side of the wheel though.

[Croustibat]

A turbo of that size spins at around 150.000rpm. If the shaft moves like you say it does, you need a new one (not a cheap isis or another ebay brand, unless you want to change your turbo again soon)

[joshfng]

Oh man I meant does NOT move*

[Mikester]

^^I had a similar issue in my 180SX... On cold start, it would smoke like a mutherfucker... then the problem would subside as it warmed up. But it still ran & performed strong as hell! My opinion is that the motor is probably getting tired and is coming due for a rebuild. It's a sign that the rings may be on their way out and/or valve stem seals, valves etc need to be reconditioned like Croustibat suggested.

What I did in the short term was install a catch can between my intake mani & PCV valve and another from my Tee fitting to atmosphere; which seemed to cure the smoking... and I only did it because I was a couple months away from stripping it down to ship to America anyway. However, when/if you do this; you will probably notice your catch cans filling up more than they should. In other words, a catch can (or two) may kill the symptom of smoking, but not fix the root cause.

Once you've ruled out the PCV, turbo, plugs, plug well seals etc; the only things left that could be causing this live between the valve cover & oil pan ;)

If I were you, I'd establish a budget and start exploring rebuild options.

GL!

Mike

[joshfng]

I've been doing some more testing. It appears as though it only smokes after decel only after I've been boosting which leads me to think turbo (but again no shaft play and no oil in the intake pipes). The car smokes a tad when it is started cold after sitting all night but after it's warm there is no smoke at idle. Also there's no smoke on decel when I've stayed out of boost.

[cotbu]

(but again no shaft play and no oil in the intake pipes). The car smokes a tad when it is started cold after sitting all night but after it's warm there is no smoke at idle. Also there's no smoke on decel when I've stayed out of boost.

Ok, 1 time! If your checking for a blown turbo and there's smoke(light, heavy, in between etc.) Taking off the turbo inlet and outlet(intercooler pipes) are only half of the equation! You found no oil in the pipes there no shaft play? there's still smoke! If you're reasoning made sense the, oil would have to travel, thru the intercooler to the intake manifold and be burnt up to smoke. We know from your answer that the compressor side is not leaking oil. you could still be leaking oil from the exhaust side! make sense? Checking the exhaust side for play, oil and grime, will most likely, have you pulling the turbo and manifold. I would recommend pulling all the plug checking them for oil, first. Then looking into the cylinders for excessive oil. If there is no oil there, then pull the turbo and manifold, if there is oil in the exhaust ports (manifold and or head)? Then it's probably not the turbo. But..... if there isn't, then the most probable cause would be the turbo.

The places where excessive oil could be getting into the combustion chamber from, are few. The job is just bigger than a turbo swap and exhaust pipe cleaning!

On the other hand, if you can live without boosting your turbo engine for the sake of it smoking? By all means disregard this post!
Or wait for someone to re post it, in a more noob friendly format! It been happening a lot lately!;)

[Croustibat]

I've been doing some more testing. It appears as though it only smokes after decel only after I've been boosting which leads me to think turbo (but again no shaft play and no oil in the intake pipes). Also there's no smoke on decel when I've stayed out of boost.


I dont know. But you need to check the turbo on the exhaust side. No play in the shaft does not mean the seals are ok. You checked the intake is ok, but there is another at the exhaust.

Have you, or have you not changed your exhaust system or the intercooler for a less restrictive one less than 4000 miles ago ? If the answer is yes, then it is a turbo seal leaking.

I also have another theory that you will absolutely not like, but here it is: you may have leaking rings. Off boost it is ok, not a lot of pressure to hold (talking about gas pressure during combustion, not boost). Boost comes, rings cant cope and leak pressure to oil pan. Pressure in the oil pan is now superior to pressure in the exhaust => turbo oil goes through the turbo exhaust seal instead of going to the oil pan.

You need to make a dry then wet compression test.


But again, this means oil goes through the turbo exhaust seal. The reason this time is not that the seal is broken, but the way it works; oil will always go where there is less pressure ( that is supposed to be your oil pan ). I think some turbos use another kind of seal that does not care about that, but not entirely sure.

That is the reason why drag cars running with tons of boost have a vacuum pump in the oil pan, as the rings WILL leak during the run, but oil still needs to come down from the head and the turbo(s).



The car smokes a tad when it is started cold after sitting all night but after it's warm there is no smoke at idle.


This has nothing to do with your problem. It is called "nightly moisture going through the exhaust".

[joshfng]

Have you, or have you not changed your exhaust system or the intercooler for a less restrictive one less than 4000 miles ago ? If the answer is yes, then it is a turbo seal leaking.

I'm not sure of this. I've had the car for 3 weeks total. I'll try to find out when the exhaust and intercooler was put on.

[joshfng]

So I talked to the old owner. He said the guy before him put the bigger exhaust on and once he got it he only drove it a couple times a week. His guess is it has somewhere around 5000 miles on it.