Shudder Symptoms: Not Always the Converter!
while duplicat- I set up some data recording tem-
ing the prob- plates on the scan tool and went for a
lem (figure 3). drive. By comparing the engine crank-
I occasionally shaft RPM (CKP) with the turbine shaft
got stray mis- RPM, the PCM calculates converter
fire counts, ran- slip. I included this and other values on
domly across the recording template.
all cylinders. While playing back the recordings,
Like most I observed the converter clutch was
vehicles, the slipping during light load in both partial
misfire moni- (EMCC) and full converter lockup. The
tor uses crank- amount of slip in full lockup was at
shaft speed times over 40 RPM (figure 4). I thought
fluctuations to this was excessive but I’d never moni-
determine mis- tored slip value that closely before.
fire. I started Just to be sure the converter was
to wonder: the root cause, I proceeded to check
Figure 3: The new Chrysler WiTech factory scan tool. I used it for both data
Could convert- other suspects from a driveability point
recording and scan tool functions. It has wireless capabilities but for the er clutch slip of view. I monitored electronic throttle
road test the USB interface was used. induce crank- values, EGR, emissions purge, A/C
right on the money: Zero PSI from the shaft speed fluctuation and fool the pressure and even the charging system
converter-off tap during lockup (figure system into random misfire counts? I generator field. All PIDs, including
2), but still plenty of shudder. intended to prove my case. ethanol % and fuel trims, were within
With the hydraulics right, I was [Editor’s Note: Yes it can. In fact, textbook perfect range.
convinced the converter clutch was the even a rough roadway can create enough Next I decided to perform an
culprit. With the scan tool, I monitored of a crankshaft speed fluctuation to set engine cylinder leakage test. That’s
the “which cylinder is misfiring” screen a misfire code on some systems.] when I stumbled upon the needle in the
Figure 4: The recording: the amount of converter slip during full lockup looks as ugly as it felt.
34 GEARS March 2010
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