Slartibartfast Posted April 13, 2012 Share Posted April 13, 2012 Occasionally, when I slam the tire carrier or otherwise bump the rear end (happened once from hammering on the rear frame), something back there buzzes loudly for a few seconds. It does this when the car is off, parked, keys nowhere near it. I found a post on Nico suggesting that the fuel pump relay was bad. I tested mine, and it's fine. It'll close the points for a moment if you thump the top of it against something... but with the key out, I can't make the pump kick on by jumpering the relay plug. This leads me to wonder if it's something on the pump itself, but I don't know why it would be getting any power at all with the key out... maybe the relay that cuts power to the pump relay is sticking? The problem is intermittent, which makes it a bugger to test. It still drives fine, and I assume it's nothing to worry about, but... anyone know what causes this? Link to comment Share on other sites More sharing options...
Trogdor636 Posted April 13, 2012 Share Posted April 13, 2012 Have you popped open your fuel pump inspection plate? Maybe you can get a better idea if the noise is coming from there? Link to comment Share on other sites More sharing options...
MY1PATH Posted April 13, 2012 Share Posted April 13, 2012 (edited) next time you hear the noise, take note; 1) is your tank less than 1/2 full? b ) if you pop the gas door open, before the noise stops, and unscrew the filler cap does the noise go away with a hissing sound? 3) this probably only occurs when you do something that shakes the gas in the tank. My guess is you are stirring up the gas and so it vaporizes more until the pressure gets high enough that it vibrates some of the filler tube (next to the pump) when is escapes. A fuel pump is more of a hissing sound but escaping vapors leans more towards a buzz. I would check for pinched vent lines, bad gas caps, and faulty charcoal canisters. Edited April 13, 2012 by MY1PATH Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 14, 2012 Author Share Posted April 14, 2012 I looked under the plate the last time I cleaned the rear carpet, and while it was pretty filthy, everything appeared intact. It's a little tough to be sure, though, as it doesn't happen often. The pressure idea's interesting... it's definitely a buzz. I'll take a look at the gas filler/canister/etc, and next time I hear it, I'll see if I can get to the gas cap in time. Thanks for the ideas. I'll let you guys know if I ever manage to nail this down. Link to comment Share on other sites More sharing options...
OlBlue Posted April 14, 2012 Share Posted April 14, 2012 Maybe you have tried this aleady but can you figure out if it is the same sound as the fuel pump by having someone else turn the key to activate the pump while you stand by the tire carrier? If you can't figure out what the intermittent mystery noise is you may as well confirm what the known noise (fuel pump) sounds like from back there. Other than that I remember a post a while back where someone was getting a gas smell in their garage after they brought the vehicle inside from the cold and the contents of the fuel tank expanded as they warmed. I don't recall any mention, of a hum, or buzz with it, but like MY1PATH said venting mightmake a noise Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 17, 2012 Author Share Posted April 17, 2012 Well, it did it again today... without me beating on it. (Tank was almost exactly, on the gauge anyway, half full.) I parked it, shut it off, and a second later it makes the noise. It did sound more like a groaning/venting sort of noise than anything mechanical (and it's definitely not the fuel pump). I didn't get the gas filler out in time to see if that would change anything. (The cap looks new, and the little white sprung bit moves freely.) When I did take it out, it made a nice loud hissing sound (like it often does when I pull the cap). I looked underneath (didn't take the tank cover off) and all the hoses etc looked solid and dry. The canister looked good too, but I don't know what a bad one would look like (besides physically broken, which it doesn't seem to be). I'll follow the hoses and things when I get a moment and see if I can find a plug/kink/etc. Link to comment Share on other sites More sharing options...
shermo Posted April 18, 2012 Share Posted April 18, 2012 mine does it aswell let me know what it is if u work it out before me Link to comment Share on other sites More sharing options...
MY1PATH Posted April 18, 2012 Share Posted April 18, 2012 The canister looked good too, but I don't know what a bad one would look like (besides physically broken, which it doesn't seem to be). I'll follow the hoses and things when I get a moment and see if I can find a plug/kink/etc. a bad canister can be filled with water, or dirt. is it heavy? there is a test procedure in the FSM to see if air can go through the ports in the proper fashion. My 93 actually did this the other day. I was slamming the brakes allot to settle in the re-indexed T-bars and the tank was on the E. It went for a good long time before I pulled the cap. With one big WOOSH everything went quiet. Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 19, 2012 Author Share Posted April 19, 2012 Hmm... I'll yank it tomorrow or Friday, and see if there's anything wrong with it. Thanks! Good to hear mine isn't the only one that does this. Link to comment Share on other sites More sharing options...
MY1PATH Posted April 20, 2012 Share Posted April 20, 2012 Hmm... I'll yank it tomorrow or Friday, and see if there's anything wrong with it. Thanks! Good to hear mine isn't the only one that does this. I was surprised mine did it, it was like coincidence. I probably would have scratched my head for a bit if I hadn't already thought beforehand when responding to yours. Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 21, 2012 Author Share Posted April 21, 2012 So, I had a look at the canister today. It's not terribly heavy, doesn't slosh or anything. I looked up the test procedure, and while I didn't test the valve with vacuum, everything else seemed to work properly just sucking on a hose. (cough, hack.) Looking at the FSM (page EF & EC 141 and 142), looks like there's another valve (the fuel check valve) which hooks onto the tank. I might just test this too... after I properly test the canister. Whatever's wrong, I'm pretty sure the check valve is what's making the noise. Come to think of it, I could probably test the valve without removing it... I'm guessing the line from it goes right to the canister. I would've gotten to it today, but then I realized the spare tire carrier wasn't shutting quite right, and tried to adjust it... great fun. (fffuuuuuu) Link to comment Share on other sites More sharing options...
MY1PATH Posted April 22, 2012 Share Posted April 22, 2012 The canister will not slosh, its filled with carbon. but if the carbon is wet it will not deal with vapors as well. but it sounds like yours is not the problem... Link to comment Share on other sites More sharing options...
devonianwalk Posted April 22, 2012 Share Posted April 22, 2012 The canister will not slosh, its filled with carbon. but if the carbon is wet it will not deal with vapors as well. but it sounds like yours is not the problem... Curious .. can the carbon be removed from the canister and reinstalled with out throwing the EVAP malfunction code? I'm going to have to tackle this on mine some time this summer. Link to comment Share on other sites More sharing options...
MY1PATH Posted April 22, 2012 Share Posted April 22, 2012 If I'm not mistaken, the evap sensor just detects weather or not the valve is doing its job or not. I Like carbon canisters, they(the purpose) don't effect the vehicle in any way other than taking up a little space and they keep your carport, garage etc from smelling like fuel. The valve messes up when it sucks up water and then you get a sensor code. If your canister is easy to get to (mine has a quick release latch) I would just remove it and cap off the lines it for wheeling and stick it back for daily driving. You can also (wd21 the pathfinder models) pull the big bottom cap off and let it air out overnight to get the water out. Link to comment Share on other sites More sharing options...
devonianwalk Posted April 22, 2012 Share Posted April 22, 2012 Good point about picking up water. I'll make sure to look into that. Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 22, 2012 Author Share Posted April 22, 2012 (edited) Okay, so, I pulled the 'fuel tank' line from the canister, and blew into the hose... and triggered the buzzing noise! I'm sure now that it's the check valve, which is probably OE (judging by the rust on the clips). I'll pop it off and see if I can clean it out... I'll probably end up replacing it, assuming I ever pay off the timing belt job. Thanks for the ideas, guys... I'll update with what I find in the valve, if I can get it open that is. Edit: Devonian, I'd almost lay money you'll find some of that red mud up in there. Edited April 22, 2012 by Slartibartfast Link to comment Share on other sites More sharing options...
devonianwalk Posted April 23, 2012 Share Posted April 23, 2012 Edit: Devonian, I'd almost lay money you'll find some of that red mud up in there. I wouldn't take that bet as I don't like giving money away! (you're probably right ) Link to comment Share on other sites More sharing options...
Slartibartfast Posted April 23, 2012 Author Share Posted April 23, 2012 Well, I finally got the little bugger out. I think it was installed before the body was mounted to the frame... not enough room in there to swing a dead cat. I checked it as explained in the FSM, and it tested good. It's got a floppy little ball valve inside that shuts it down if it's not upright (so it can't dump fuel into the canister if the truck flips over). I couldn't get it open to clean it properly, so I shot some WD-40 into it to see what that would do, and it came out looking like tea... it's probably just gummed up in there. I shot a little lithium in there as well, blew it in as well as I could, and re-mounted it. I doubt I fixed anything, but at least I know it still does its job. Link to comment Share on other sites More sharing options...
tmoore4512 Posted May 14, 2012 Share Posted May 14, 2012 Just found this thread... Mine does the same thing from time to time, but I swore it was just the fuel pump kickin on for some reason... Got my gears turning now... Link to comment Share on other sites More sharing options...
Alkorahil Posted May 16, 2012 Share Posted May 16, 2012 (edited) Mine does this all the time after driving it when I turn it off,.when it is very low on fuel (1/8th or less). My fix has always been to put gas in the truck so I dont run out of gas. (and the sound goes away too.) Edited May 16, 2012 by Alkorahil 1 Link to comment Share on other sites More sharing options...
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