Odd Fuelling Issue.

[whysub]

I am very happy with my W124 300E but i seem to have an issue that has stumped me. When i collected it 4 weeks ago it had been standing for some months. On the first drive I stopped after a mile or so and put some petrol in it. Pulling away it was very hesitant, what felt like a "fluffing" under load. I thought it could just be the damp,seeing as the car had been unused. After 75 miles or so it cleared and got better and better and jas been running perfectly. I took it out today (it had been parked up for a few days) and it was fine, no hesitancy at all.

Filled it up with petrol and pulling away from the garage the same hesitancy was there again.

I am trying to think what it could be - the only thing I can think of is it is linked to having a full fuel tank. Any ideas as I am stumped?

[bortaf]

Blocked breather in the tank? try adding fuel but only half a tank and see if that changes anything? does the filler suck in air when the cap is removed?

[whysub]

I did think of the tank venting (happens on motorbikes occassionally) but its fine in that there is no "rushing air" sound when taking off the fuel cap. Funny how it occurs with a near full tank-venting problems usually show uo when the tank is getting low. This was noticed within 25 yards or the pump. Baffling me.

[cobblers]

Is there a load of curse word in the tank getting sloshed around when you fill up and blocking the strainer?

[taurus]

I'd reckon there is some water in the tank which is getting stirred up when you add fuel. Not uncommon in tanks that have stood for a while.

[whysub]

Makes sense-there was an awful lot of condesation on the glass and on the underside of the bootlid ( but carpets and seats bone dry. Another question now- is water heavier than petrol?

[andyborris]

Pretty sure the answer is yes, remember an old fire demo, with petrol burning on top of water!

[colnerov]

Hi, if there is water in there, then put some Methylated spirits in the tank, apparently it removes/soaks up the water and then gets burnt by the engine.

Colin

[taurus]

Jan 28, 2015 23:46:51 GMT colnerov said:

Hi, if there is water in there, then put some Methylated spirits in the tank, apparently it removes/soaks up the water and then gets burnt by the engine.

Colin

Yes - water and petrol won't mix, but alcohol (ie the ethanol in Meths) and water do mix, and the resulting mixture will then itself mix with the petrol. Do it with as full a tank as you can and about half a bottle of meths. The alcohol/water mix will then be absorbed by the whole tank of fuel so it shouldn't affect running at all.

Alternatively - if you know a source of petrol with ethanol already in it use a tank of that.

[Rich]

Jan 29, 2015 8:06:24 GMT taurus said:

Alternatively - if you know a source of petrol with ethanol already in it use a tank of that.

All UK petrol? ;P

[taurus]

Yes - but isn't most of it only a small amount? I was reading about it a while back due to the problems ethanol causes for classics due to corrosion of the fuel system - and the worry was that some brands were introducing petrol with much higher percentages of ethanol.

Or it is now all containing higher percentages of ethanol? In which case I'd better do something about it.

Looking back over some old threads I remember now why I lost the plot with the amount of ethanol in fuel - long story short it was due to guys who know far more about chemistry than me arguing over the best additives to combat ethanol corrosion - and my attention span wandered.

I'll start a new thread rather than derail this one.

[baggabones]

If it was stood unused for a while the petrol that is in it will go stale and also "varnish" the injectors or carb, I'd do a full strip and clean

[ejenner]

Could you have a pulsing fuel line or fuel pump anywhere? Would be interesting to know if it is only with a full tank.

[whysub]

Yes-this fluffing only occurs when fuel is put in. This is the third fill. As the fuel in the tank goes down it runs perfectly. It had only a bit of petrol in it when i picked it up (does anyone sell a car with fuel in it now?) - I fuelled it up within 2 miles.

When I say fuelled up, I only put 46 litres in everytime as it makes calculating thr mpg from the trip meter simple. Still cant fathom which it runs properly when the tank contents lessen. Could the fuel pump run differently under these circumstances? Its baffling me.

[taurus]

It'll run better once the fuel settles down. The water will collect in the bottom of the tank below the pickup. It's only when you fill it up and stir the contents of the tank up that the water droplets are being mixed up into the tank.

If it settles down quite soon after filling up I'd bet that's the cause.

[whysub]

Thanks Taurus and all. I wont be using the car until Sunday, so any sediment or water in the tank will have settled by then and the car should run without the hesitancy.

If this is the case I'll try meths in the tank to get rid of anywater, as I am unable to scrabble about under the car because of my poor knees! Or would I be better off finding some one to drain the tank? Questions, questions, questions.........

[taurus]

Try the meths first. It can't do any harm. If it's no better after that then there may be muck in there as well which will need cleaning out.

[bortaf]

Jan 30, 2015 12:25:08 GMT taurus said:

It'll run better once the fuel settles down. The water will collect in the bottom of the tank below the pickup. It's only when you fill it up and stir the contents of the tank up that the water droplets are being mixed up into the tank.

If it settles down quite soon after filling up I'd bet that's the cause.

Below the pickup? this is an EFi engine the fuel pickup will be at the bottom or below the bottom of the tank IE in a sump ?

[taurus]

I don't know the specifics for that particular tank - but there's nearly always a small area below which fuel is actually taken in. That's where I'd guess water has settled. It's only one possible cause of course, but given the car's been standing and it only seems to 'fluff' immediately after fuelling, it's what I'd check first.

[bortaf]

Jan 31, 2015 9:15:01 GMT taurus said:

I don't know the specifics for that particular tank - but there's nearly always a small area below which fuel is actually taken in. That's where I'd guess water has settled. It's only one possible cause of course, but given the car's been standing and it only seems to 'fluff' immediately after fuelling, it's what I'd check first.

It's behind the rear seat and the fuel take off it at the very bottom with a remote fuel filter and pump under the floor so there is no way water can get "under" the fuel pickup.

I would check the cap as well as the fuel filer, filter will most likely need changing by now anyway and cheap caps can have condensation issues and or sticking carbon contact? if it was a jag i'd be inspecting the carbon cannister and breather system for these symptoms so may be worth thinking about if nothing else solves the issue.