Last post on Sep 17, 2012 at 11:52 AM
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Engine, Fuel System
#457 of 460 91 S10 Blazer running rich, stalling on deceleration
Sep 15, 2012 (11:45 am)
91 S10 Blazer Sport, auto, 4X4, 4.3L TBI. 189000 miles. No trouble codes. Code 12 only. Recent post #171 in Chev. Blazer forum. No response. Guess no one is interested in dinosaurs. Since that post have learned more how to use scanner. The O2 sensor generates abt. .550v max. at idle. and does not reach necessary .620 [for closed loop in this engine] until operating at 2000 or more RPM for close to one minute. In city driving it rarely meets this condition so remains in open loop most of the time. I think this explains excess fuel and stalling at sudden deceleration. Much to rich in open loop. Runs great on the interstate and gets 22mpg there. Could be the exhaust gas not hot enough at low speed, for the O2, but cannot find why. The O2 is new [ third one ] , MAP new and test normal. Coolant sensor new and changed twice. Thermostat as well [ 195F]. EGR is new. Vacuum abt. 16 at idle abt. 22 at 2000RPM. Does have a little jitter. Should not be necessary but I am tempted to change to a heated O2. Might solve the immediate problem but may be a crutch. Hope one of you Super techs can solve where four shops and I have failed. I love this old lady.
#458 of 460 Re: 91 S10 Blazer running rich, stalling on deceleration [rfletcher]
Sep 17, 2012 (7:32 am)
Is the O2 sensor a 3 wire unit, with the built-in heater? Maybe the heater circuit is open.
#459 of 460 Re: 91 S10 Blazer running rich, stalling on deceleration [srs_49]
Sep 17, 2012 (11:52 am)
Thanks, No, it's a new replacement O2 but the original one wire type. That's why I considered changing to the heated version. Real pain to do and a lot more expensive but would probably solve if not correct the problem. Seems a vicious circle. As I understand it, among other things, excess fuel will tend to cool the exhaust and non functioning / cooler than normal O2 will cause excess fuel. Maybe someone smarter than me can explain it.