Where does the fresh air come in for the AC/Heat?

[99-LS1-SS]

I have a 1985 K10 regular cab short bed truck. My cab fills up with exhaust fumes every time I drive the truck. It seems to get worse as I'm stopped at a light. I just put a new exhaust system on the truck thinking that would help the fumes and smell but it didn't. Now I'm wondering what else could be going on.

Where does the fresh air come in for the AC/Heat? I'm going to start there and try to trace the path to see if anything jumps out at me.

[bodyman922]

I believe everything comes in through the cowl vent along the windshield. If fumes are getting in I would check around the 4 wheel drive shifter in the floor or see if there are any holes in the firewall. Also a long shot but if there is any rust holes in the back sides of the rockers or by the kick panels that could allow fumes in as well.

[99-LS1-SS]

I have a whole about the size of a baseball in my driver's side rear cab corner but, I didn't think that could be the source. I guess it could. I didn't think about the shifter. I'll check that and I'll fill the whole in the cab corner.

[bodyman922]

I don't think the cab corner would be the entrance, but I've been wrong before. You said you put new exhaust on, does that mean from the manifolds back or cat back or? The only way to seal everything up for sure is to put all new gaskets in everything, like where the manifolds meet the head, where the pipes meet the manifolds, etc. After that is all checked then weld it all up. Other then that I don't know what else to try.

[motornut]

hows the hood seal to the cowel
I've had smoke vapour appear out of the coloum turn signal area

[99-LS1-SS]

Originally Posted by bodyman922

I don't think the cab corner would be the entrance, but I've been wrong before. You said you put new exhaust on, does that mean from the manifolds back or cat back or? The only way to seal everything up for sure is to put all new gaskets in everything, like where the manifolds meet the head, where the pipes meet the manifolds, etc. After that is all checked then weld it all up. Other then that I don't know what else to try.

It was from the manifolds back. I use new manifold to exhaust pipe gaskets. I won't be able to weld it up for a few weeks.

Originally Posted by motornut

hows the hood seal to the cowel
I've had smoke vapour appear out of the coloum turn signal area

The gap seems normal. I did notice a gap between the cowl area and the firewall but I don't know it that is normal. If anyone has a picture I could compare. I haven't seen any smoke coming from the steering column. But, I'll check where the column comes through the firewall.

[motornut]

this is where it goes across the front(holes red/blue line
I've just found my seal to put it back,got new clips(some were broke)
hows the engine blow by
I think thats where mine comes from
out of the valve cover and syphons to the holes in the coloum
also have seen the gasket at the coloum/firewall hold salt/water/rust out leaving a hole ...

[spencer_41188]

if your using headers i would dobble up the gaskets both on the head and the colector this was the only way i could stop the leaking headers short of a belt sander

if your using a stock cast header i would see about taking them to get magnafluxed and machined they may be worped or cracked

all the exhaust should come out the tail pipe you shouldnt smell it in the engine bay or cab

you can use soapy water on first start up befor it gets too hot or just look for the soot at all the joints ... if your using the u shape exhaust clamps they tend to leak if there not just right ... too tight or too lose they will leak and once they get hot they tend to break if you mess with them

pain in the butt i know been there done that
good luck

[99-LS1-SS]

I haven't had a chance to look for the place that the fumes are coming in yet because it's dark when I get home. I don't think my blow by is nearly as bad as your is/was. I want to look closely at the 4WD shifter boot and the intake at the cowl and go from there. I seem to recall there was a sizable gap between the firewall and the cowl cover. I might need to see about addressing that.