I have failed emissions on my 91 Ford Ranger about 4 times. Have put new plugs/wires, air filter, had egr valve put on by a dealer. Had a new catalytic converter and exhaust put on, have used gas treatment. Reading was higher after trip to mechanic. Hydrocarbon is what has failed me. Went from 374 to 651 after I went to this car care center. Took it back to them and they changed the pvc valve and put a new line on, then it started missing worse and engine light stays on and the tach won't work now. Any ideas please. The only idea I can come up with is not taking it back to that mechanic, because every time I do it gets worse. Have been dealing with this problem about a month now. I have run out of what I thought it might be. Thanks.