GM 3.8

Hi all,
Have a 2009 Buick Lacrosse 3.8L that has slight oscillating power surges between 37 and 42mph, with no
driveability issues other than this one and no DTC codes. Graphic monitoring of the engine ignition timing
with Torque software indicates oscillations between 23 and 27 degrees in precise agreement with the power surges.
Lab scope indicates Ignition Control Module (ICM) X3, X18 and camshaft signals to the ICM are within parameters.
IC timing control from the Powertrain Control Module (PCM) to the ICM appear within parameters. Has anyone
experienced this same issue and if so were you able determine a solution?

you should look at what your transmission is doing when the surges are going on. Watch your over drive and your torque converter lock up. See if they are switching back and forth

Thanks for the response carriedi. I failed to mentionthat was my first concern. I had a transmission rebuilder here at a local transmission
shop perform a test drive and he ran both transmission and engine diagnostics with his Snap-On Versus and concluded from the results
and experience (42 years in field) the transmission and converter are not the issue and he could not determine cause of problem.

if you can feel it, it should show up somewhere. Engine,trans... Does it show up in the engine rpm's when you graph it?