I just changed my fuel filter (some gunk) and used Chevron Techron fuel injector cleaner....I only put 6 oz in my tank, and the check engine light went off IMMEDIATELY. It came back on for a mile or two then back off. Before I did this it was only CONSTANTLY. I had used a whole bottle of B-12 chemtool (don't recommend) and the light started coming on all the time. I changed the pcv valve, O2 sensor, and now fuel filter. I think The chemtool really made all that crap in my tank congeal and clog my filter a bit and especially my injectors. I used seafoam, and it worked for a tank, but that was it. So I heard good things about Chevron and tried it. The erratic pulsing is gone, the engine is smoother, and my fuel gauge is working for the first time in 4 years.....amazing stuff.

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'94 Ranger 2.3 2wd 5 speed manual