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Shudder Bug
When road testing a vehicle, it can be very difficult to determine whether the shudder you are feeling while driving under load is caused by an engine misfire or a transmission or torque converter problem. "Educated guesses" just don't cut it here, especially when the difference between a right and a wrong guess may mean removing a transmission that has nothing wrong with it. For an accurate diagnosis of these symptoms, try this:
- Attach a portable lab scope or graphing digital multimeter to the oxygen sensor signal wire, then take the car for a road test.
- Have an assistant watch the scope for any sudden drops in the oxygen sensor signal voltage that correspond with the vehicle shudder symptoms.
- The decrease in the oxygen sensor voltage is caused by an increase in the oxygen content in the exhaust, which indicates that an engine miss has occurred.
- If the vehicle shudders, but there is no corresponding change in the signal on the scope, it's time to look at the transmission and/or torque converter more closely.
Stacy Glenn
Glenn's Automotive
Tyler, Texas
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