You need to fix all the rust holes in the floor.

When you open the window you create a vacuum that will suck in fumes big
time if there is any hole or crack.

I also find turning on the heater blower helps as well as opening 'both'
side windows at the same time in my Jeep CJ7. I have a new body tub and
exhaust and still have to be careful about fumes. One window open only
will allow fumes to suck in through the rear window snaps and zippers.

A friend in a Jeep TJ couldn't understand whey he could not stay awake
driving. He had the 3 rear windows out and with the door windows
closed, he was getting gassed bad. I figured it out the first time
driving with him.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Ltine wrote:
>
> Hi Everyone,
>
> I have been reading your post for a long time but have never
> submitted one until now. I hope that somebody out there can help me.
> I have a 68 ford Bronco, Brand new 302cid, 351 windsor heads (bigger
> valves), Holley Truck avenger carb, and a brand new bronco c4. The
> reason I have posted this message is because I have a problem I just
> cant beat. I have exhaust fumes coming into the cab. This may sound
> easy to correct at first, but I have already done all of the obvious.
> I have replaced both of the mufflers, the pipes only have about 3000
> miles on them, and for good mesure I have checked them anyway. I did
> the donughts off of the manifolds which (did seem to help a little),
> and I have put exhaust tips on just to make sure it is clearing the
> back of the truck.
> The exhaust system is 2" and it is straight back without a cross over
> of any kind. And finally the manifolds are stock but not cracked or
> broken in anyway, and have brand new gaskets and I have checked the
> torque several times.
> However the only time that I have any problem is when the window
> is down. I have heard tidbits about a vortex being created by having
> the window down, that sucks into the cab. I'm not sure this is true
> but any help will be greatly appreciated. Anyone who has ever ridden
> in an old Bronco knows that in the summer there is no way to not open
> the window or take off the top in the summer. I am truely desperate
> here. I am a competative athlete and cannot take the fumes. I'm
> afraid that if I cant solve this problem I will have to get rid of my
> old bronc, and thats too bad because with this engine set up she
> screeams!
>
> Thank you in advance for any help, I throw myself on the wisdom
> of the group.