There are an extreem amount of people on this forum that are suffering from this problem. This took me three weeks and a lot of money to figure out. Models: 1999-2000 cadillac escalade 1995-2000 chevy/gm S/T models 1996-2000 chevy/gm C/K, M/L, G, P models 1996-2000 olds bravada all with 4.3l, 5.0l, 5.7l, 7.4l engines -VINs W, X, M, R, J - RPOs L35, LF6, L30, L31, L29 If you suffer from: No, hard, or slow start, backfire or "kickback" during crank start "grinding or unusual noise during crank, DTC P0338 or, no DTC, or intermittent DTC not related to the issue. (Replace Crank shaft Position sensor) Condition: Backfire during crank/start "kickback" during crank/start "No/Rough start" slow/hard crank start cracked or broken block at starter boss broken flywheel/missing teeth/unusual wear starter broken not able to crank engine Cause: Crank shaft position sensor has been struck by the crank position gear/key on the crank shaft that is only intended to disrupt the magnetic feild to provide crank position. This will cause the ECM to command 50+ degrees of timing during crank causing cylinder pressure to build way beyond normal operating cylinder perssure causing sever damage to the starting components i.e. starter, flywheel and attaching hardware. Over the years the forward main bearings begin to settle/wear which is a normal condition and or the timming cover has become warrped or settled. This causes the crank shaft position sensor to rest on the cranksharft timing position gear/key effecting the output voltages of the sensor causing the timing to increse or decrease by as much as 50 degrees. Sometimes the condition occures once the vehicle reaches it's normal operating temperature. Effect: Either your vehicle will try to start, backfire and not start which would lead you to belive there is a timing issue and or start at a low rpm and studder until it steadys out at the correct rpm-this is also common or randomly start fine and other times not start all while not setting DTC code or setting random DTC codes!!!! Very difficult to find with scanner! Inspection: Using a 10mm socket remove retaining bolt located on crank shaft postion sensor braket found on the bottom of the timming cover just behind the harmonic ballancer. unclip the harness and remove the harness to allow access to the sensor. Remove the sensor with a slight tug and inspect. you should see no sratches/scrapes or abrasions!!! Replacement: replacement is absolutely required if any of the above conditions are found!!! New sensor includes shims used to correct this problem use both shims included. Lastley, in the new box that the new crank shaft position sensor comes in a tech sheet will include even more detailed instructions on how to properly shim sensor. Hope this helps, good luck!