Fuel Line Whirring
 

Hi all,

I'm new to this forum, having recently purchased a DRB Cobra (302 Windsor motor).

Can anyone assist with a fuel noise problem.

After recently cruising upto Lamington National Park (QLD), I experienced a high pitched whirring noise from somewhere near the rear fuel line.

I was travelling up a mountain (a big hill) consisting of a lot of short straights and hairpin bends. Half way up, the whirring noise increased to a point that I pulled over and rested for a while. After starting again the noise had gone.

I think it may be air in the fuel line, but am curious to know whether anybody else has experienced anything similar.

Note - there was no effect on the performance.

PCC (Peter)

Hi Peter and welcome to the forum.

Is your car injected? Are you running the pump in the tank? What was your fuel level like?

I've found with some regular (non Cobra) cars I've had with in tank fuel pumps that the lower the fuel level gets the louder the pump gets. With the tank in the Cobra being right behind you and the 3/4 empty tank acting like a sounding board it can get quite loud. Also as you are cornering and accelerating the pump isn't always covered by the sound deadening fuel so you get more noise. When you stoped and then re started all the sloshing fuel settled down and the pump was submerged again keeping it quiet.

I guess if you think of it how an acoustic guitar works. If you twang a guitar string in the free air it doesn't make much noise but if you put a hollow box behind it it pumps the volume up dramatically.

The other noise I've noticed that becomes more aparent is the fuel return line squirting fuel back into the tank. As the fuel level drops this seems to make more noise too.

It's just a theory and I could easily be wrong. It would be interesting to try it again with a full tank.

Cheers

Craig, Scott and Les will be happy to have another Banana Bender to boost their numbers on this forum. They are a bit out numbered by us Mexicans :D

Are you coming to the nationals in October?

Cheers

Thanks for your prompt reply Mike - You must be like me and work from home.

Banana Benders hey - a new one on me.

Pineapple heads maybe!

As i'm a pomme living in Queensland I feel a bit like a bitzer (bits of this, bits of that) - Anyway the sun keeps shining.

Back to the technical issue:

Yes the cobra is fuel injected with a 70l tank and in tank high pressure fuel pump.

The tank was between half and 3/4 full as there aren't many fuel stops in the "mountains". However the roads were pretty steep in areas so may be the fuel was sloshing to the back of the tank (or maybe not).

I am aware of the fuel return noise although this is more of a hiss (maybe thats why the cars are called cobras!)

The noise I experienced was quite a high pitched constant whine increasing in severity as I climbed higher - Never done it since.

Regards the Nationals, when are they held in South Brisbane as Sydney / Canberra is a little far to travel (although I do fly into Sydney on a regular basis).

Finally,

Craig, Scott and Les - Where do you hide out as we would like to catch up with you some time.

PCC

Hi Peter,

The nationals are being held in Goulburn NSW from Friday 3rd October till Sunday 5th October. It'll be a good do with more than 100 Cobras expected. There will be plenty of us builders and enthusiasts that haven't got our cars together as well. There should be a bunch of guys from the Queensland club coming down in convoy.

Craig (750HP), Scott (Oz Venom), and Les (Rebel 1) are all down in Brisbane I believe. They will probably chime in here shortly.

As for the fuel noise I'm stumped. Change in the outside air pressure as you climbed and the venting of the tank? Dunno. Some of the other guys here might have some ideas for you.

Cheers

Hi Peter,
I can only come up with what Mike has already mentioned.... My low pressure pump (lift pump to the swirl pot), and the Bosch high pressure pumps make a lot higher pitched, louder noise when they are run dry. It's also really bad for the pump to run them this way.... :( Mine ran like that for about 3 seconds while I was priming them for the engine dyno, so hopefully no long term damage done!

Have you been down to the Sanctuary Cove breakfast yet? The Cobra Club has a breakfast on the first sunday of each month. It's well worth dropping in there to meet everyone.

This weekend is a huge motorsport weekend down at Murwillumbah. http://www.speedontweed.com Might see you down there!

Thanks Craig (805hp wow, that makes my 302 sound small).

Regards the fuel noise, I don't think there's permanent damage as its been fine since.

Look forward to catching up with you at Sanctuary Cove, if not when the Nationals are on then definitely November.

I've got a weekend of annoying, but minor electrical issues including a cold start problem (I'm sure my car's a female as it does what it wants to do when it wants to do it) so will have to forego Tweed.

Once I'm properly set up, we will be seeing you around the tracks. If you're around the Bayside drop me a message and we'll meet up.

PCC (Peter Craig)

Hi Peter, Welcome to the madhouse. Now, we dont care if you are a relocated pommy, as long as you live in Queensland then you're one of us.

If you were a Victorian..then maybe we'd chat to ya...maybe not...If you were Victorian and had a Chevy in ya cobra..well then ... :(

Now..to your tank. In tank pumps set up a resonance..a high frequency vibration if you will. With production tanks (mostly plastic) this isnt a problem, but with metal tanks, this resonance can become audible.

The resonance becomes audible if the tank touches some other fixed chassis component..ie a bracket/chassis rail etc. Obviously going uphill caused the fuel to move back in the tank, maybe causing the tank to move in its mounting ever so slightly, thereby touching some fixed component.

Thats why it is a good idea to put thin rubber gaskets under tank mounting flanges if using in tank pumps.

Few years back a mate with cobra used to get this funny noise from the back end. After months of searching we found the problem to be the fuel filler tube that entered the tank. He had not allowed enough gap between the tank filler tube (the 2"pipe welded to the tank) and the pipe to which it joined with a short length of hose from the fuel filler.

On some throttle openings the two metal pipes would just touch causing the resonance to become audible. The movement of the tank was barely noticable but sufficient for those two pipes to touch.

A hacksaw to remove 1/8" of pipe fixed an annoying problem.

Maybe something similiar...worth a look anyways.

Make sure you keep in touch

Welcome Pete,

I think you're going about this all wrong.
Bernie Knight has already came up with a solution to your problem a couple of days ago in an other thread.

You need Bernie to design your exhast system.
With a couple of Bernie specials running down the side of your Cobra,
you'd find it hard to hear an atomic bomb go off,
let alone a little squeek in the fuel tank.:D

I like your thinking Jason.

I had a clapped out old car years ago that rattled and squeaked and carried on. I fixed all the noises by putting in a louder stereo.

Cheers

Hey

Whats the problem you cannot hear the complaining from the passenger. Slow down **)

Mike when you where in the States did you meet or catch up with Hershal :confused:

He emailed me yesterday and he is an agent for Robert Logan.

He is based in Arizona. I remember you saying you met some guys over there and travelled to the Spring Fling :confused:

Cheers all

Bernie

Yep, I met Hershal.

He's a top bloke. Scott and Craig drove his Cobra all the way up from Texas to Ohio for the fling. I got a few laps in Hersh's car with Scott at the wheel on the banked oval.

Cheers

Back to the old ear plugs routine - cheap!

Have you ever tried pushing a Cobra up a hill - who says these cars are light - or maybe its the fact that you don't want to put your hands on the paintwork.

Its a good job I've got a landcruiser and snatch rope - good ol 4bies.

Next purchase - a battery charger.

PCC (Peter)