I do a lot of metal polishing as I have several classic British bikes and Autosol is the only metal polish I use. On really grubby tail pipes I use really fine wire wool and Autosol to get the crap off the just a microfibre cloth and Autosol to polish up.
I tried the Autosol method once and it worked a treat. After about a week the pipes were black again.
i bet your car was a diesel. diesels have very dirty engines and loads of sh!t comes out of the exhaust.