my engine has around 9k miles since itwas rebuilt and it started to smoke at high RPM .

I thought it was the turbo and replaced my twins with a single setup

I did but still smokes at high RPM , I've redone the PCV system twice over and made sure the oil wasnt getting pressurized

The car only smokes when i let off the gas .

So above 5k RPM I let off and there is a cloud of smoke behind me and my AFR gauge reads about 10 afr when it does this .

when the AFR gauge reads --- or nothing at all the smoking stops . I thought I had figured it out as leaky injectors . BUT why then does it only do it at high RPM?

maybe the higher vacume pressure of high RPM is sucking fuel into the engine ??

OR is it just that OIL when burnt also reads on an AFR gauge ?

I will post a video Of it happening at an autocross

 

 

Being pig rich will cause black smoke. All afr sensors see is oxygen. Low oxygen means rich high oxygen means lean.

Normally when you let off on fuel injected vehicles it stops fuel injection until near idle speeds or you give it gas again. Your afr gauge should show full lean with the gas let out and coasting. If it continues to inject you will end up extremely rich and likely get black smoke during closed throttle coast.

 

Besides meters reading oxygen not fuel:

Burning oil heavily will kill a wideband. Every so often, I let my oil get overfull and the intake will suck a quart or so of oil at high RPM. Besides the giant cloud of smoke, the wideband gets killed.

 

when the AFR gauge reads --- or nothing at all the smoking stops . I thought I had figured it out as leaky injectors . BUT why then does it only do it at high RPM?

Did you put in new cast iron oil seal rings when you rebuilt?

I notice the high rpm smoking when you let off the gas in engines with out of spec oil seal rings or old, old, old, cracked oil ring o-rings.

...Or if you still have a vacuum line from your oil overflow to your intake manifold as the term PCV refers to.
Proper race sump ventilation will eliminate the vacuum line to the intake which is for emissions in the stock PCV system.

 

I didnt rebuild it myself so I couldnt tell you , But the core used on the motor was extremely low miles


I tried running the PCV configuration without the PCV valve connected to teh engine and didnt really make a difference .

at this point it seems like its either an oil issue or leaky injectors . But since I already dumped a couple thousand between the single turbo setup and other things . I figured I'd be sure . granted the cheapest solution may just be to get the injectors rebuilt and see if that fixes it .

 

Indeed Well if thats the case I'm hoping thats whats going on , the car itself isnt running rich , But when I close the throttle at high RPM , It reads rich around 10 afr , and as it goes down to around 4k it goes back to absolute lean or --- what ever you might call it .

and I do know that O2 sensors read oxygen But I guess that means that if there is burnt oil in the exhaust than it would also read 10 AFR since it wont destinguish between fuel and Oil


well i'm truly hoping its not an oil control issue . and its just excess fuel . for some reason .

 

Are you running an OMP?

I ask because if you've deleted it you could, and probably should, have the ECU set up to still inject a minor amount of fuel during decel so that your engine still gets lubrication. This probably isn't directly related to your smoke, but I know good tuners that will def do that.

 

Is decel fuel cut turned off in your ECU?

 

I have my computer tuned to throw all the fuel in the world at the engine during decel just for this reason. That and the little bit of extra cooling you get.

As a side bonus (for me anyway) it completely eliminates pops and bangs on decel. No kaboom, no fire, just quiet.

 

its deleted


It was deleted on my previous motor , But I decided to add it to this one for that reason , But it failed on me . and thinking it might be the reason it was smoking I deleted it Just incase

 

hmmm thats ironic , when I turned on the fuel on decel . it would be fire fire fire all day long . I was afraid the back of the car would catch fire so i disabled it ,( but this was before I had the smoking issue )


on a side note I sometimes get Very loud bang when i lift off in high rpm