Why does my exhaust sometimes smoke and others times not?
12-18-2004, 08:01 PM
#1
Why does my exhaust sometimes smoke and others times not? During autox today, I came off a run and fumes were pouring out the rear tips. I had the cutout open but fumes were coming out of the tips, but not the cutout 
Didn't smell like coolant, but it was a whitish color. The GM Master tech who happened to be there thought it may be related to the PVC, the PVC routing not being ideal for high lateral acceleration, and/or oil in my intake. Sam thought it might be oil washdown in the cylinders from running so rich (SD tuning at 13.0 AFR) but the oil didn't smell like gas.
I've got the LS6 valley cover with the rear two PVC vents blocked off, and I have an clear inline fuel filter between the manifold cover and the stock PVC. Although there was a film on the inside, there was very little oil in the clear tube. I took off the throttle body and I was able to wipe a brownish residue from the inside of the plenum entry.
We stopped for lunch, it was smoking leaving the facility. I drove it a few miles roundrtrip, and the fumes disappeared. It was a bit spontaneous the entire day. Later I heard a whistling sound coming from the rear of the car, and it seems to be the fuel pump. However, I monitored the AFR while it was smoking and it was 12.6 <-> 12.8.
I am running a SD tune, with the MAF/O2's/AIR not in use at this time. But I've never seen this occur in daily use - and I've been on the SD tune for at least a month now.
Ideas?
Didn't smell like coolant, but it was a whitish color. The GM Master tech who happened to be there thought it may be related to the PVC, the PVC routing not being ideal for high lateral acceleration, and/or oil in my intake. Sam thought it might be oil washdown in the cylinders from running so rich (SD tuning at 13.0 AFR) but the oil didn't smell like gas.
I've got the LS6 valley cover with the rear two PVC vents blocked off, and I have an clear inline fuel filter between the manifold cover and the stock PVC. Although there was a film on the inside, there was very little oil in the clear tube. I took off the throttle body and I was able to wipe a brownish residue from the inside of the plenum entry.
We stopped for lunch, it was smoking leaving the facility. I drove it a few miles roundrtrip, and the fumes disappeared. It was a bit spontaneous the entire day. Later I heard a whistling sound coming from the rear of the car, and it seems to be the fuel pump. However, I monitored the AFR while it was smoking and it was 12.6 <-> 12.8.
I am running a SD tune, with the MAF/O2's/AIR not in use at this time. But I've never seen this occur in daily use - and I've been on the SD tune for at least a month now.
Ideas?
12-19-2004, 05:50 PM
#5
It was a 3-day practice designed to kill my current race tires so I can buy the new breed :-)
The rear is still rubbing (passenger side I think). I've got longer studs for the rear hubs. I'm getting some noise from the differential so I figured I'd haul it over to Advanced Driveline and have them perform a service on it and check/reset the tooth pattern. Since they'll be in there I might as well have them swap the studs and put on spacers as well. Then bring it over to you to to re-align the rear-end. I want to check the front too, as one street tire is corded on the inside, and the other (while bald) isn't corded.
I don't recall it smoking at all today. Someone said they saw some puffs while on course, but nothing at idle.
The rear is still rubbing (passenger side I think). I've got longer studs for the rear hubs. I'm getting some noise from the differential so I figured I'd haul it over to Advanced Driveline and have them perform a service on it and check/reset the tooth pattern. Since they'll be in there I might as well have them swap the studs and put on spacers as well. Then bring it over to you to to re-align the rear-end. I want to check the front too, as one street tire is corded on the inside, and the other (while bald) isn't corded.
I don't recall it smoking at all today. Someone said they saw some puffs while on course, but nothing at idle.
Last edited by JimMueller; 12-19-2004 at 09:03 PM.
Trending Topics
12-20-2004, 12:32 PM
#11
This may not be your problem, but sometimes condensation in the exhaust (usually in the muffler itself) will cause the exhaust to appear white in color. It is really just steam. That would explain why it was coming out of your exhaust tips but not out of your cut-out (the water was laying in the muffler and wasn't present in the system further "upstream" where your cut-out is located.). After the condensed water burns off, it will stop steaming. Later, when the exhaust cools, it can condense again and start all over. Just depends on the weather conditions (ie. temp and humidity). My car does this all the time. My Borla will steam out of the driver side (the side that is actually routed through the muffler), but it won't steam at all on the passenger side (the side that comes right off the intermediate pipe). That is how I know the water is condensing in my muffler. Look for water dripping out of your exhaust tip(s). If it doesn't smell like antifreeze, it's just condensation. Hope this helps.
Last edited by GC99TA; 12-20-2004 at 12:38 PM.
