Mechanics

CHEVROLET TAHOE GAS PROBLEM

2002 Chevrolet Tahoe • 158,000 miles

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.
Regards,
Alex
Avatar
Joedonlooney
October 26, 2012.




The thing I have pointing to in your pic is the fuel pressure regulator. Check the hose for fuel if it has it the regulator is leaking. Also clean the throttle plate on both sides with choke cleaner. Then drive it and see if it clears up. Then spray the choke cleaner around manifold looking for a vacuum leak andfinally check compression if you find any less thatn 20% then check the offending cylinder for a bent pushrod/broken valve spring etc. As far as the hum it may be the engine fan pulling air in as they get quite loud sometimes.


Hmac300
Oct 29, 2012.
Missed sending pic back lol.
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Hmac300
Oct 29, 2012.
Thank you for the analysis. As I stated, I replaced the fuel pressure regulator, and began hearing the noise (note how the blue marking is missing for the replaced FPR) which seemed to be emitted from the described line extending behind the engine. I know how vibration travels, so I was more concerned that the noise was maybe exprienced previously by someone as an obstruction in the line or something like that. I wanted to make sure to get to it if that was in fact a possibility you might have known about. It's difficult to describe the noise without hearing it. The intermittent "hum" has become more infrequent, so I'm keeping my fingers crossed that maybe the rings in the FPR are seating correctly or whatever is causing it is working itself out gradually. One of the things I had done initially when I replaced the MAF sensor was clean the choke plate, which did help a little with the initial problem of rough idling. I have not done it again since the FPR was replaced, so I will try and do this again. I have not detected any leaks in the line or the manifold. I have not performed a compression test. As I stated, I was not getting a code for a particular cylinder, and I have not done any testing on any particular cylinder as a result. At this point the occasional burst of "hum" is the only attendant problem with the fuel line that I can tell. I am not getting any further codes from the reader, and both banks seem to be firing fairly equally by the diagnostics. Again, I only began hearing it after I replaced the FPR.

I appreciate you writing back. I apologize for the delay in replying, but the delay leads me to another question, if you don't mind. During the past few weeks, I had the starter replaced and I had (what was originally diagnosed as) a slow leak in the gasket around the oil pan, so I had the gasket replaced at the same time as the starter. Afterwards, the oil leak has worsened. There is a second small gasket just above the oil filter (NOT the ring between the filter and the body that you replace with an oil filter regularly), instead it is between what I believe is called the oil filter adapter plate and the block. The plate is shaped kind of like a small Twinkie with bolts at either end. The gasket evidently is problematic on these engines, and my mechanic told me to pick one of the gaskets up and he'd put it in for free. He also told me that my rear main engine seal had perhaps begun leaking (I had not seen it leaking previously). However, my main question has to do with the sudden worsening of the oil leak. I have a hard time believing that the leak behind the adapter plate+the leak from the pan seal went from minimal to 4-5 drops per drive left after my car has been sitting. Maybe he's inept at replacing the gasket? How many miles does it take for a main seal to go, on average? How many mechanic hours would you estimate replacing the main seal would require (2WD)?

Thanks again.


Tiny
Joedonlooney
Dec 6, 2012.
The original gsket for that 'twinkie" is silicone, and it is a complete gasket or should have been so it may be an inept mechanic or not torqued right. So if just a noring was installed it may have caused it but it should be a regular gasket that looked like it had 1 or 2 orings on it and if the oring pealed from the gasket it wold leak. Main bearing seals can last a long time and normally don't leak t your stated mileage. They are all one piece now and the trans has to be pulled to replace it. So figure the cost from that.I'm sending two pics, one of wht the oil seal on side of engine shold look similar to and the other of the crank seal which is aplate witha seal and has a gasket that cold be driping causeing your main seal leak. How ever i'd fix the outside one an d wash the engien and keep an eye on it as it may be some type of trans seal that is leaking from that area. Besides if you aren't using more thatn a a quart of oil ever 1000 miles or so don't worry about it unless you are really anal about your vehicle. Meaning you want no leaks, etc.


Hmac300
Dec 6, 2012.

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