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Car Forum / Dodge / Dodge Trucks / March 2005Shifting Strangeness 98 Ram
1998 Ram 1500 , 318, 4x4, OD auto, 3.55:1 gears, SLT extended cab, 130K miles, std. tires, all "stock". Trans fluid/filter changed every ~20-25K miles, engine oil changed at 5K mile intervals, tune-ups at normal intervals. Currently driven daily for commuting 80 miles around DC beltway and in stop/go traffic, about 6 trips coast to coast open road with several more to mid-west, used for camping in mountains once or twice a year, about 400 miles off road total and never driven hard, fairy frequently haul up to 500 lbs, never tow anything, have only a cab height cap on the bed. Replaced a speed sensor at ~100K. The past few months at cruise speed 50 to 60 MPH in top gear under light throttle the RPM may occasionally fluctuate by about 50 RPM, don't notice it at higher speeds/RPM. Sometimes a headwind or slight grade will bring this on. Coincident with this behavior about 1 take-off in 10 from dead stop has rough shifts through first two ranges. Don't notice any drop off in "performance" otherwise, engine has always been slightly underpowered and changing plugs, etc. doesn't change situation. No idiot lights, but trans definitely isn't shifting normally and the RPM fluctuations while suggestive the engine wants to up-shift, aren't what I consider normal for this truck, feels more like trans slippage. I am the original owner and only driver. Thanks in advance for any advice. mole Sounds like the torque converter is unlocking and then locking back up. You can test this by driving at a steady speed and very lightly tapping the brake pedal. This will cause the torque converter to unlock momentarily and cause a slight increase in RPM's. The most common cause of this is a bad throttle position sensor. Other sensors and the brake pedal switch are also suspect. > 1998 Ram 1500 , 318, 4x4, OD auto, 3.55:1 gears, SLT extended cab, 130K > miles, std. tires, all "stock". Trans fluid/filter changed every ~20-25K [quoted text clipped - 19 lines] > > mole > Sounds like the torque converter is unlocking and then locking back up. > You can test this by driving at a steady speed and very lightly > tapping the brake pedal. This will cause the torque converter to unlock > momentarily and cause a slight increase in RPM's. The most common cause > of this is a bad throttle position sensor. Other sensors and the brake > pedal switch are also suspect. [snip] Thanks miles, I'll try what you suggest and report the findings tomorrow. I forgot to mention that I observe the behavior at most any operating temperature or air temperature. Another thing, would the TPS or other sensor problems show as fault codes w/o showing on the dash idiot lights as "Check Engine"? Thanks, mole > Thanks miles, I'll try what you suggest and report the findings tomorrow. > [quoted text clipped - 3 lines] > Another thing, would the TPS or other sensor problems show as fault codes > w/o showing on the dash idiot lights as "Check Engine"? A faulty TPS will not likely cause a check engine light. It simply senses the throttle position so a faulty TPS just gives bad data and the computer doesn't know to trip a fault code. I have also heard some independent Dodge techs tell me improper electrical filters cause the torque converter to unlock. I'm not sure if they are referring to spark ignition noise being picked up or what. But this normally occurs on new Dodges right from the start. [snip] > A faulty TPS will not likely cause a check engine light. It simply > senses the throttle position so a faulty TPS just gives bad data and the [quoted text clipped - 4 lines] > if they are referring to spark ignition noise being picked up or what. > But this normally occurs on new Dodges right from the start. Okay, tested very light application of the brakes at steady speed on flat roadway. When the brakes began to engage the revs shot about 300 RPM up briefly as the torque converter unlocked. I repeated this several times. The wavering I noted as a suspected problem or symptom was only about 50 RPM. Suppose that means start playing 20 questions with the TPS? Thanks, mole > [snip] > [quoted text clipped - 18 lines] > > mole I replaced mine in about 10 minutes (99 ram 318) My truck was doing the same thing yours is. Only cost a few bucks. > > [snip] > > [quoted text clipped - 20 lines] > I replaced mine in about 10 minutes (99 ram 318) My truck was doing the > same thing yours is. Only cost a few bucks. Thanks Will and miles, I'll p/u a TPS and install it. mole |
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