can sporatic tach cause engine to stumble? - Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum



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  #1  
Old 08-29-2017, 02:13 PM
ttblazer04 ttblazer04 is offline
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2004 Chevy TrailBlazer LT
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Join Date: Aug 2017
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can sporatic tach cause engine to stumble?

First post: My 2004 trailblazer 4.2 has started to have some issues. The Cam actuator and sensor have been replaced, but ever so often the tach will stay at zero when motor is running. The idle seems to be good (most of the time) even if tach remains at zero. As you accelerate the tach does rise, but stays 700 to 1000 rpm's less. Problem is this started and then transmission went out, replaced transmission and everything seemed fine for a week. Then tach starts this intermediate problem. It appears that if not driven a few days it works fine for a week or so then it happens again. Any way this tach issue can cause the motor to stumble or miss? only does this at 40mph+, and only if tach is having these issues. I have read most of the threads and it seems that everyone says replace stepper motor, which I plan on doing, just want to make sure I don't have more problems! Thanks in advance for your help
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  #2  
Old 08-29-2017, 03:45 PM
EnvoyBoy2004's Avatar
EnvoyBoy2004 EnvoyBoy2004 is offline
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2004 GMC Envoy SLT
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You are apparently having two problems. The tach issue is most likely a bad stepper motor and will not cause the engine to stumble. The engine issue needs more diagnosis. Are there any codes, is Check Engine light on?
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Old 08-31-2017, 07:26 PM
ttblazer04 ttblazer04 is offline
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2004 Chevy TrailBlazer LT
Imperial Blue Metallic 4.2L I6 2WD
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Codes- both active and stored

Sorry for the delay, thanks for your reply...
Active code P0442- which it says is small leak detected in emission system

Stored codes were P0128- B camshaft position timing over-advanced or system performance

and P0128- Thermostat coolant below regulating temp.

Thanks again for any ideas.
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