Originally Posted by Diseasel300

It isn't so much fuel quality, but lack of maintenance. People dump fuel in and run the car until the filters clog so badly that the engine stalls or loses power. By then, there's a ton of crap all spread throughout the fuel system. Diesel Purge should be run every so often to clean out the fuel system just like injector cleaner in gas engines. If it's been a long time since the fuel system was cleaned, you can expect some seriously nasty stuff to come out in the first purge cycle. Mine came out pitch black the first time I did it. Looked like engine oil. Car had 175K on the clock at the time and I'll guarantee it had never been done before.