Under the Hood: Diagnosing carís problem requires careful experimentation

McClatchy-Tribune Information Services

June 10, 2019

Q: My son has 2014 2.0 L Kia Forte. Sometimes it seems to buck/shudder or feel sluggish at certain speeds. On the highway itís fine. He has had full electronic analysis done on the car and has not found a solution or any codes or errors. Iíve driven it, and it almost feels like itís in too high a gear for the rpm the motor is at. I suspect it has something to do the transmission but I havenít been able to find any information on how the transmission works on this car. Overall, he really likes the car but is frustrated. The local KIA dealer was no help at all. Any help would be greatly appreciated.

ó Dan

A: It can be challenging sometimes to determine whether a condition such as you describe is caused by the engine or transmission. Your Forte is equipped with a six-speed automatic transmission with a pretty good track record. How about starting by using the manual shifting mode to identify which gear is being used at the moment and how you might be able to alter the effects of the symptom?

Begin by establishing the most noticeable symptom onset condition, for example, during mild acceleration at 37 mph at full operating temperature. Take note of engine rpm (speed) at this time. You may be correct that the engine speed is low for conditions; however, most vehicles try to lean in this direction for the best operating economy. Try bringing on the symptom on a long straightaway where you have room to select a lower gear to bump up rpm a bit, and perhaps a second bump as well. Does the symptom change or disappear? Does the manual mode indicate which gear is presently selected?

Hopefully, with experimentation you can map the speeds and load when the transmission upshifts/downshifts, and use manual mode to identify which gear is which. Also, when the symptom appears, does the engine grumble/shudder consistently (as expected if itís in too high a gear for conditions), or does it thump and jerk randomly (perhaps a single cylinder misfire, possibly due to a faulty ignition coil)? A fault of this type will typically show first under a slight engine lugging condition before worsening.

The bottom line is for you or your son to become the Symptom Master, capable of taking a tech for a ride and demonstrating exactly when and how the symptom onsets, and how it can be manipulated. Most powertrain faults result in a diagnostic trouble code being set or other identifying data as viewed on a scan tool. An early onset/intermittent fault such as a leaky ignition coil may not stir up enough trouble to be flagged by the management system.

Q: I bought a 2018 Chevy Silverado with 110 volt receptacle in the lower dash. It only provides 150 watts! What were they thinking! I expected at least 1800 watts (15 amps) so I could use a saw or drill. It will only power a phone charger. I checked the 2019 model with the receptacle in the truck bed and itís still only 400 watts! Your thoughts?

ó Dave

A: I agree the capacity on these is close to useless ó a marketing gimmick! I took matters into my own hands and installed a 1500 watt inverter under the back seat of my truck in order to do real things such as you mentioned. When doing so itís important to run very thick (2 gauge or larger) 12 volt cables to the inverter, beginning with a 150 amp fuse, as about 100 amps of current is needed to create the needed 120 volt juice. (1500 watts/14 volts=107 amps) Make sure to run the engine as large loads are occurring to avoid draining batteries!