Hey everyone, I picked up a 1991 Ranger with the 2.3L I4 a while back. Shortly after getting it home we realized it had a blown head gasket. We pulled the engine apart and replaced the head gasket along with a whole assortment of other components while we were at it. When we were finally confident with how it was running again, we took it for its e-test and were shocked by the results. NOx levels passed with flying colours...HC failed at high idle with 148/98 and passed at low idle with 180/200. But CO levels failed miserably on both trials. It read 7.86/0.55 at high idle and 7.31/1 at low idle. Does anyone have any idea what could possibly cause the CO levels to be so high?? The truck runs like a dream, starts right up and no knocks, pings, etc. It has new plugs, wires, ignition coils, clean air/fuel filters, and O2 sensor. The only clue that something is off is that the engine seems to bog down for a split second if you really (and I mean REALLY) step on the gas quickly. The check engine light does come on once in a while, so when I get the time I plan to test for OBD-I codes...But does anyone have any ideas to point me in a possible direction? I also checked the resistance of my injectors with a multimeter and they were all slightly high...around 17 ohms where my chilton manual says to be looking for 12-16. I don't feel like that could account for SUCH a high CO reading though. Vacuum, compression, and fuel pressure tests all also gave values within spec. I don't mind spending the time/money to swap out some more sensors or something, but my main concern at this point as that with levels that high, it's not going to improve enough...has anyone ever heard of having values that high? If I take it to get tested again I would at least like it to have a chance...would I be further ahead to just cut my losses? Sorry for the long post! Just trying to cover all my bases. Thanks in advance. Cheers.