Diagnostic              Mass Air Flow Sensor                      Buick 3800 Ignition Coil Pack    A diagnostic is performed to find the cause of any of the following: Failed E-Check No start Hard start Engine starts then stalls Stalls on deceleration "Service Engine Soon" or "Check Engine" light is on Rough running engine Misfire Hesitation Lack of power Poor fuel economy ABS light is on Air Bag light is on Charging system not operating properly And much more...                      State of the art tools and equipment are used to perform a diagnosis. Scan tools with the latest updates Interro PDA, OTC, Tektronix, and Snap-on digital oscilloscopes and ignition scopes Waekon on-car injector flow bench And much more...                             The cost for a diagnostic is $55 plus tax.  In most cases, you will not be charged an additional diagnostic fee.   A leaking fuel pressure regulator on a 92-95 GM 4.3L Vortec with Central Port Injection (located under the intake manifold).  Notice how the left side is washed down with fuel.  This is a common problem and causes a very rough idle and a misfire as well as a rich running condition with black soot coming from the tail pipe