The first thing is to figure out why it is putting unburned fuel in the exhaust. No codes?

Could be a faulty injector, sensor, thermostat, etc. You didn't give us much to go on.

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Dave

'05 325xi
'10 E70 35d
'85 911 Carrera
'66 911 Work in progress
'91 Chevy C1500
'95 Jeep Cherokee
‘18 Jeep JLU