Question about 1994 GMC Sierra
'94 GMC Z71 4x4 automatic
57K actual miles on the truck.
New spark plugs 3 mos ago.
Check engine code: 12 -- O2 sensor reading lean condition
I get an intermittent 'bouncing/flutttering' of the Tach at about 2400-2900rpm. It feels like a cylinder dropping out, but not completely. I have had a plug wire come loose and it doesn't feel like that. It's more subtle. Shortly thereafter the check engine light comes on. Keep driving and it goes back off, tach bouncing stops. There is a noticable loss of power as I cannot maintain my normal speed while towing. (65mph) Outside temp does not seem to affect it. (Phoenix, AZ) Alternator voltage, Engine temps all normal.
I am suspecting a failing crankshaft sensor, O2 Sensor, or both. I am changing out the rotor,cap & plug wires because they are due, but I doubt this will fix it.
Point me in the right direction. If you need more detail, email me. Please don't reply with a vague, wide sweeping suggestion.
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Posted on Jan 02, 2017
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