I would look for an exhaust leak under the hood then look under the car, there will be execisive carbon build up at or near the leak.

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'85 F250 6.9L diesel 2wd XL XC LB Centurion, Gone
'95 Mercedes E 300 Diesel W124.131 with a OM606.910 and just over 200k on the clock, needs top end engine work and a transmission.
2000 S500 W220 with a 5.0L V8 gas power.

On my wagon I get diesel smoke smell in the car if I open the sunroof without opening any windows. I suspect air is getting pulled past bad rear hatch seals, since the sunroof creates lower pressure in the car and the rear hatch is in a high pressure area. Other than that, I only smell the exhaust if I'm backing up.

I agree with the suggestion that you may have an exhaust leak. If exhaust leaks in or near the engine bay it can get drawn into the HVAC system.

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1981 Mercedes 300TD, 1994 Honda Civic Del Sol
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