Check compression on cylinder #4. If none or low, you may have a headgasket problem, broken/bent pushrod/collapsed lifter.
Generally the ign. Module will affect all cylinders not just one.
When you relocate to sea level it is also a good idea to disconnect the neg. Battery cable for a minute. This will let the ECM learn the new air pressure and richen up the fuel mixture.
Friday, October 3rd, 2008 AT 7:25 AM