Curing The Annoying Underhood "Buzz" From the Evap Canister
I loved pretty much everything about my 1996 Toyota Limited 4Runner 4x4 after I bought it.... everything that is, except for an annoying buzzing noise that came from underneath the hood whenever I shut the engine off. It was particularly bad on warm days. Every 30 seconds or so there would be a 'bzzzzz" sound from somewhere around the brake master cylinder. This intermittent buzzing would last for hours after shutting the engine off. Sometimes it would come back first thing in the morning after the sun came up and started warming the car. At first I thought it was an electrical problem, like a short circuit or electrical arcing, and I was quite concerned. A little googling, however, led me to the conclusion that it was just benign gas venting noise that wasn't causing any harm. But it was still annoying and I wanted it to stop.
The problem lies with the evap charcoal canister, which vents fuel tank emissions. The canister is located on the driver's side fenderwell in front of the master cylinder. The buzz sound is actually a resonance in the charcoal cannister that is excited by escaping gas. It was addressed by Toyota Service Bulletin EG002-97. Here's how I stopped the noise:
1. I went to my local Toyota dealership and had them call up the TSB. The counter guy printed out the instructions for me and told me that the replacement part I needed to buy was something called the "EVAP Canister Hose No. 1". The part cost $22.95 and was not in stock. I paid for it and two days later it showed up.
2. After I had the part in hand, the first step was to remove the old hose from the canister. Mine was really tough to pull off, and after struggling for a bit I took a utility knife and physically cut the damn thing off. In doing so, I dislodged another hose and nearly snapped off one of the hose clips underneath the hood. Old lesson relearned: take your time and be careful with knives and recalcitrant parts underhood.
3. Once the old hose was off, I installed the new "hose," which isn't really a hose at all. It's actually a small plastic air chamber box with a hole in its back side and a rubber hose coming out of its bottom end. It also has an adhesive strip on it that is supposed to secure the unit to the evap canister once installed. Despite cleaning the canister and pressing very hard, I couldn't get the adhesive strip to stick very well. Oh, well. I doubt it will come off; the hose connections are a pretty tight fit and the new part feels very secure in place, even without the adhesive.
4. And that's it: problem solved. It took all of ten minutes to make the repair, and now the noise is permanently gone. A few people have posted on the forums that they hardly notice the buzzing on their 'Runners, and have never felt like making the fix. Thats fine for them, but not me. For $22 and a little time, this fix is well worth the effort if you hate the noise like I did.