Fuel Tank Banging Noise

[chimpboy]

I''ve had my ''94 4LTR Chimp for about two months but from about two weeks ago the fuel tank has developed a banging/popping noise. I put it down to expansion/contraction of the tank due to the petrol deing drawn out by the fuel pump. But its getting more frequent and really quite loud sometimes. My two concerns are 1) why has it only just developed it after six weeks of not doing it and 2) is it anything to be worried about, should I get it looked at? Any help appreciated....

[philr]

If this noise is similar to that from a metal oil can as the air replaces the oil as you're pouring it out (only a bit louder), then you're fine. This used to scare the **** out of me at first as I had images of the hand brake sticking on or something. I usually get this after I have parked the car for an hour or so and then set off again. This is just down to the presure in the tank equalising. If your noise is not lieka metal can thump, then I can't help.

[ATG]

Griffith forum "noisy fuel tank" from March discussed this. They also suggested the sender for the fuel guage (float attached to a potentiometer) might be swinging around ... which seems a bit unlikely. Their thread:- http://www.pistonheads.com/gassing/topic.asp?topic_id=846&hostId=0 Anyone know how/where the air normally bleeds back into the tank? If your clanking is getting worse, maybe whatever route the air normally takes is getting obstructed. One other thing springs to mind ... are you driving the car harder now that you've had it a few months? The more quickly you're dumping fuel into the engine the harder and more quickly that vacuum is going to build up. Edited by ATG on Tuesday 14th August 12:52 Edited by ATG on Tuesday 14th August 12:52

[trefor]

The metal noise is definitely a feature but I think there may be a breather pipe. If you remove the boot panel on top of the tank (big cardboard thing with carpet on it) then you should see some pipes and a widget (not been there for a while - someone else will probably know more. The sender unit does clonk on the tank side too - I get this quite often and if you listen you can hear it getting softer and softer and the oscillation decreases.

[chimpboy]

Thanks guys, you've put my mind at rest somewhat. The theory about me driving the car harder now I've had the car a while did cross my mind, maybe I kept the tank fuller most of the time when I first got it so there was less air to expand/contract in the tank. I'll just put it down to a feature of the car, one of many

[ATG]

Interesting that, Trefor. I stand corrected. re. the hard driving theory ... only one way to test it, and that's to drive it even faster and see if it gets even worse. "I was doing it in the name of science, your Honour".

[Neil Hyde]

Word of warning Gent's . Had exactly the same problem on my 94 Chimp . Allowing the banging to continue ultimately dislodges the baffles in the tank . Bitter experience , as I had to get a new petrol tank installed which took eight weeks to obtain from the factory !! Led to believe that there is a return line carbon filter which can become soaked with the the water it is there to remove . Cleaning this should stop the banging and save you a new tank !!

[trefor]

I had the carbon filter replaced just after I got my car (under warranty and it was at Henley H so who knows if they actually replaced it!). I don't know if it would cause these problems, but it is definitely something worth checking.