Grey smoke at high rpms

Hughes · 05-28-2008, 09:59 PM

I currently have an NA S5 with a supposedly rebuilt streetported engine.
I have racing beat exhaust and thats it for mods.

I'll let my car heat up, make sure the pressure is up and then drive it nicely until its at proper temp.
When I open the throttle, then get to about 5k or so, let off the gas, it will usually back fire and a trail of grey smoke will come out. Some times its greyish blue.
This will happen everytime I give 'er hell. But after I stop, go eat or something, come back and start it up, it might not do it.

The exhaust smells really rich, but when it backfires, its not an oil or gas smell, its much more strong.

I'm guessing its oil seals or it needs a full tune up. It has tons of power still and doesnt feel awkward redlining it either.
I was going to do a compression test, but that won't tell me if the oil seals are good or bad, correct?

RETed · 05-29-2008, 01:04 AM

Do the compression test anyways.
This will most likely eliminate the fact if the motor is tired or not.

Too bad the engine needs to be taken apart to figure out exactly what is wrong.

-Ted

Ender · 05-29-2008, 04:02 PM

...technically, backfiring is ignition of fuel in the intake as opposed to the exhaust. Afterfire is what this is. It's fairly common, especially for RX-7's. Deceleration of the motor, even hitting the clutch and letting the revs drop only enough to shift, can let the motor to run rich enough to afterfire (if you want me to elaborate on why, I can). Since you said this mainly or even only happens when you really get on it it makes me think even more that it's normal afterfire (however afterfire can harm things. you could blow exhaust gaskets or in a horrible case maybe harm a turbo or engine internals if the afterfire is powerful enough with the ignition point close enough to the block*). If you could get video that would be great, but I would urge you to use a camera mount or passenger to record for you. Smoking a little during afterfire would not worry me, but if it's quite a bit of smoke then you may have degenerative internal issues that should be addressed. That said, I agree that it would be prudent to take a compression test.

*...damn, I just realized terrible afterfire might have been what did my old motor in. The apex seal groove was hogged out, the seal came loose during startup and locked the motor. The groove could have been smacked open by all the afterfire I was getting between the block and turbo...

Hughes · 05-29-2008, 07:48 PM

I could probably get a video of it tomorrow.
I think Im going to pick up some plugs and wires and see what happens to.
I was trying to demonstrate the smoke for a friend, went to about 7-8k, and no smoke so...

05-28-2008, 09:59 PM	#1
Hughes The Newbie Join Date: May 2008 iTrader: (0) Posts: 4 Rep Power: 0	Grey smoke at high rpms I currently have an NA S5 with a supposedly rebuilt streetported engine. I have racing beat exhaust and thats it for mods. I'll let my car heat up, make sure the pressure is up and then drive it nicely until its at proper temp. When I open the throttle, then get to about 5k or so, let off the gas, it will usually back fire and a trail of grey smoke will come out. Some times its greyish blue. This will happen everytime I give 'er hell. But after I stop, go eat or something, come back and start it up, it might not do it. The exhaust smells really rich, but when it backfires, its not an oil or gas smell, its much more strong. I'm guessing its oil seals or it needs a full tune up. It has tons of power still and doesnt feel awkward redlining it either. I was going to do a compression test, but that won't tell me if the oil seals are good or bad, correct?

05-29-2008, 07:48 PM	#4
Hughes The Newbie Join Date: May 2008 iTrader: (0) Posts: 4 Rep Power: 0	I could probably get a video of it tomorrow. I think Im going to pick up some plugs and wires and see what happens to. I was trying to demonstrate the smoke for a friend, went to about 7-8k, and no smoke so...