Engine Performance problem
1999 GMC Suburban V8 Four Wheel Drive Automatic 200148 miles
Engine misses ocasionly during normal driving. I have tried to make it miss and can`t seam to find a way to make it miss. I don`t know if it is in the firing or fuel injection. It doesn`t set a code. I have hooked a Nemisys scanner to it to scan some of the sensors and could not find a problem. I hooked a fuel pressure gauge to it and drove it down the road, and the fuel presure stays around 62, 63 to 58, 59.I have tried to pay attension to when it does it and it semes to do it mostly when you top a hill or a grade and letting off the accelerator. It doesn`t matter if I am driveing or I have the cruise on. I can mash the accelerator to the to the floor and it has good power, goes thru the gears good and doesn`t miss, so I don`t think it is a fire break-down problem. It only does it during normal driving. And it has a slite hesitation off idle. The spark plugs are AC platinum, and haven`t been in long. I has a 5.7 Vortec. This is what I have done and this problem started when the fuel pump went out. I replaced the fuel pump, replaced the intake gaskets with the Fel-pro gaskets with the metal reinforcement. Replaced the fuel pressure regulator, replaced the MAP Sensor, replaced the dist. Cap and rotor. Have checked all engine grounds by cleaning and retightening them. Also added a ground wire to the bracket the coil is mounted on. Also replaced O2 sensor, Bank 2, sensor 2 after geting a code for this.
Engine misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel