Short version, but I will try to describe as much as possible: The only appreciable work I've had done on my Tahoe is replacement of the fuel pump by the dealership approx. 50,000 miles ago when it failed. Several months ago I began experiencing rough idling and difficulty starting. Eventually, my SES light illuminated and I pulled P0300 and P0175 from a code reader. I went through replacing the parts in the chain of potential problems that I felt competent in replacing after searching for information online on what the causes of the codes could be. I replaced the plugs, plug wires, MAF sensor, and all four oxygen sensors. The MAF sensor and the oxygen sensors provided short relief until the symptoms returned, each time with a slight variance (well, more regularity) in the behavior of the rough idling/starting. After searching further, I found info with regards to replacing the fuel pressure regulator. I replaced the fuel pressure regulator and all symptoms disappeared (aside of the fact that my starter solenoid keeps sticking now, replacement being put in soon, tired of climbing under my car to hit the starter with a wrench to get it started). My current problem is that I am now getting an intermittent, irregular "vibration" (for lack of a better term) and attendant noise. It sounds like an irregular, intermittent, unpredictable "hum" that occurs in extremely short bursts. Sometimes I do not hear it at all, and I do not hear it while freeway driving - I try to listen for every little noise my car makes. I can hear it in the cabin and outside of the car. I noticed that when idling, the fuel gauge sometimes minutely jumps in concert with the vibration. It appears to be strongest/loudest in the larger (by diameter) of the two lines exending vertically from the fuel rail immediately behind the fpr and thereafter louder along the branch of that particular line that wraps around the rear of the engine to the other side (the "top" one of the two in the picture). It also feels strong in the other branch of the same line that extends under the engine cover to the other side. I've suspected a bad batch of gas began the problems, but I can't be certain. I dont' know if that line is apt for cracks/vaccum leaks, as the intermittent nature of the noise suggests, or clogs, and I don't see or smell any additional fuel coming from the line. I understand the basic mechanic's logic of "replace the part, " however, I am more interested in knowing the potential causes and diagnosis along with the remedy, as opposed to just the remedy. These are my first experiences with doing anything with my Tahoe, but I'm decently mechanically inclined and not awed or afraid of working on anything that wouldn't be made infinitely easier or more time effective with a lift - anything that needs a lift more than taking out a fuel filter or the aforementioned oxygen sensors, I'll go to a mechanic - but I'd like to know what to discuss with a mechanic before the need arises to discuss it. I also don't know the names of these parts surrounding or extending from the fuel rail, and I've realized I can waste a lot of time simply trying to find the names of these parts online (I realize I should buy a shop manual). Any help with the cause of the noise would be much appreciated.
Friday, October 26th, 2012 AT 7:30 PM