exhaust fumes entering cab when windows open.

[screbo]

Hi all.
during the summer weather(sic)  i have been driving with windows down, and getting exhaust fumes into cab,  does not seem to happen when they are shut, so tend to think not coming up through engine bay into cab, it occurs even if driving into a breeze, when one would think the fumes would be blown to the rear of the vehicle. Also,
The blower on heater unit not strong enough to blow feather over.
Any ideas please.

Thanks
Screbo.

[Dell Boy]

Got no answer on fumes. Check exhaust for leaks. Blower should be very strong. There is a foam filter in the bottom of the heater on the air intake. Could be blocked. Derek.