Question about 1994 GMC Sonoma

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I have 4 cyln 5 speed gmc .truck just started skipping or motor hesitation under acceleration,i changed plug, wires,pcv valve.old plugs r white on the heads.i know its lean.please help .has anyone had same prob with a solution?i cant afford to **** money away on a bunch of could bes.thanks for help,,,,note.skip does not occer all the time but just seems to be getting worst

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I hear you!

Bad input = Bad output

Start testing the computer inputs -

1) Air Charge Sensor (Resistance measurement - OHM meter needed)

2) Coolant Temp Sensor (Resistance measurement - OHM meter needed)

3) Crankshaft Sensor (Test procedures off the ignition amplifier)

4) Detonation Knock Sensor (This can cause your symptoms if there are any rattles in the motor or exhaust pipe - like a loose heat shield or bracket causing the rattle will be picked up by the knock sensor - which in turn retards the timing causing a stumble and hesitation)

5) MAP (Manifold Absolute Pressure) Sensor (make sure the plug contacts to it AND all of your other inputs are not corroded - also check the vacuum line going to the MAP and make sure there are no leaks, cracks....)

6) O2 Sensor (Would normally show up on computer as needing replacement - not always though )

7) Throttle Position Sensor (this is a variable resistor, which can and does get wear spots on it - sending incorrect voltages to computer causing your stated symptoms too. A good analog meter would be nice to test this. engine off, key on - You can tap into the voltage side and watch the needle carefully while slowly opening throttle to wide - and back to close. If the needle on the meter moves smoothly from one side to the other without and dips or jerking motions, then the TPS is fine - of course the voltages need to be within parameters)

You can find all of the testing procedures and vehicle specific data at

Good Luck.

Posted on Oct 03, 2010


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