code 42- electric spark timing code 43- Knock sensor circuit code 44- 02 sensor- lean exhaust detected These are the 3 codes I am gettin on a 91 Chevrolet 3500HD with a 454. I went to looking for the kock sensor which I thouht was on the passenger side of the engine just around the starter, thats where it is on my other pickup and there is nothing there. I have a plug coming out of the harness on that side of the engine with 2 green wires, is this the plug to it? Is the knock sensor supposed to be on that side in the coolant gally? The only sensors I can find are one behind the harmonic balancer on the oil filter side that is long and cylindrical which I am pretty sure is the oil pressure sender, the other is in the head on the oil filter side which is the tempurature sensor. I cant find the knock sensor for the life of me, if it doesnt have one I am sure that is why all the codes are popping up. The guy that had it before me really jacked this pickup up bad. Any information would be a big help.